Satellite Communication

Lecture-1

Dr Shahab Ahmad Niazi

Satellite Communications

Introduction

bull General concepts

bull Needs advantages and

disadvantages

bull Satellite characteristics

bull Orbits

bull Earth coverage

bull System components and design

bull Power sources

bull Communication characteristics Spectrum and Bandwidth

Channel capacity

Frequency and Wavelength

Path losses

Antennas and beam shaping

Text

bull Course Book

Satellite Communications 4th Edition

Dennis Roddy

Reference Books

1 Satellite Communications 2nd Edition T

Pratt C Bostian and J Allnut

2 Satellite Communications Systems 5th Ed

Gerard Maral Michel Bousquet

Why Satellite Communication

bull The Earth is a sphere amp The microwave frequencies

travel in straight line but to connect two regions very far

away on the two side of the sphere the link requires lot

of repeaters because of Earth‟s curvature

bull A single satellite can do the magic linking the

continents with one repeater

Motivation to use the Sky

Regions of Space

Space is defined as a place free from obstacles

It can be divided into three regions

bull Air Space -gt region below 100 km from earth‟s surface

bull Outer Space -gt also called cosmic space and ranges from 100 km up till 42 000 km It is mostly used by communication satellites

bull Deep Space -gt Regions beyond 42000 km fall in this category

Satellite

bull It is a repeater which receives signal from

Earth at one frequency amplify it amp

transmit it back to Earth at other

frequency

EARTH STATION

bull There are two earth station in a simple

Satellite communication link One

transmits the signal to satellite called

transmitting Earth station

bull The other receives the signal from

satellite called receiving Earth Station

UPLINK amp DOWN LINK

bull The communication link from

Transmitting earth station to satellite is

called Up-link

bull The communication link from satellite To

receiving earth station is called Down-

link

What is a satellite system

bull A satellite system consists of one or

more satellites a ground-based station to

control the operation of the system and a

user network earth stations that provides

the interface facilities for the transmission

and reception of terrestrial

communications traffic

How a satellite works

bull A satellite stays in orbit because the gravitational

pull of the earth balanced by the centripetal force

of the revolving satellite

bull One Earth station transmits the signals to the

satellite at Up link frequency Up link frequency is

the frequency at which Earth station is

communicating with a satellite

bull The satellite transponder process the signal and

sends it to the second Earth station at another

frequency called downlink frequency

Advantages of Satellite Communications

over Terrestrial Communications

bull The coverage area greatly exceeds

bull Transmission cost of a satellite is independent

of the distance from the center of the coverage

area

bull Satellite-to-satellite communication is very

precise

bull Higher bandwidths are available for use

Disadvantages of Satellite

Communications

bull Launching satellites into orbits is costly

bull Satellite bandwidth is gradually

becoming used up

bull The propagation delay is larger

Active and Passive Satellites

bull Active satellites are used for linking and also for processing the signals

The linkage is known as bent pipe technology where processing like frequency translation power amplification etc take place

Active satellites employ bdquoRegenerative Technology‟ which consists of demodulation processing frequency translation switching and power amplification are carried out Block used for this purpose is called transponder

bull Passive satellites do-not have on-board processing and are just used to link two stations through space

Low cost - Loss of power ndash not useful for communication applications

Historical Overview

bull 1945 Theorist named Clarke studied that satellite orbiting in equatorial orbit

at radius of approx 42000 km would look as if stationary if moving at a

specific speed 3 satellites at a space of 120 degree apart can cover the whole

world Evolution of the concept of GEO

1950rsquos ndashPutting the pieces together

1048708 1956 -Trans-Atlantic cable opened (about 12 telephone channels

per operator)

1048708 1957 First man-made satellite launched by former USSR (Sputnik-

1 LEO) It was used to identify atmospheric density of various orbital

layers It provided data about radio signal distribution in ionosphere

1048708 1958 First US satellite launched (SCORE) First voice

communication established via satellite (LEO lasted 35

days in orbit)

bull 1960rsquos ndashFirst satellite communications

bull 1048708 1960 First passive communication satellite (Large balloons Echo I and II)

bull 1048708 1962 First active communication satellite (Telstar I MEO)

bull 1048708 1963 First satellite into geostationary (GEO) orbit (Syncom1 communication failed)

bull 1048708 1964 International Telecomm Satellite Organization (INTELSAT) created

bull 1048708 1965 First successful communications GEO (Early Bird INTELSAT 1)

Historical Overview

bull 1970rsquos ndashGEO Applications Development DBS

1048708 1972 First domestic satellite system operational (Canada)

1048708 1975 First successful direct broadcast experiment (USA-India)

1048708 1977 A plan for direct broadcast satellites (DBS) assigned by the ITU

1048708 1979 International Mobile Satellite Organization (Inmarsat) established

Historical Overview

bull 1980rsquos ndashGEO Applications Expanded Mobile

1048708 1981 First reusable launch vehicle flight

1048708 1982 International maritime communications made operational

1048708 1984 First direct-to-home broadcast system operational (Japan)

1048708 1987 Successful trials of land-mobile communications (Inmarsat)

1048708 1989-90 Global mobile communication service extended to land mobile and aeronautical use (Inmarsat)

Historical Overview

bull 1990+rsquos NGSO applications development and GEO expansion

1990-95

1048708 Proposals of non-geostationary (NGSO) systems for mobile communications

1048708 Continuing growth of VSATs around the world

1048708 Spectrum allocation for non-GEO systems

1048708 Continuing growth of DBS DirectTV created

1997

1048708 Launch of first batch of LEO for hand-held terminals (Iridium)

1048708 Voice-service portables and paging-service pocket size mobile terminals launched (Inmarsat)

1998-2000

Mobile LEO systems initiate service and fail afterwards (IridiumGlobalstar)

Historical Overview

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Satellite Communications

Introduction

bull General concepts

bull Needs advantages and

disadvantages

bull Satellite characteristics

bull Orbits

bull Earth coverage

bull System components and design

bull Power sources

bull Communication characteristics Spectrum and Bandwidth

Channel capacity

Frequency and Wavelength

Path losses

Antennas and beam shaping

Text

bull Course Book

Satellite Communications 4th Edition

Dennis Roddy

Reference Books

1 Satellite Communications 2nd Edition T

Pratt C Bostian and J Allnut

2 Satellite Communications Systems 5th Ed

Gerard Maral Michel Bousquet

Why Satellite Communication

bull The Earth is a sphere amp The microwave frequencies

travel in straight line but to connect two regions very far

away on the two side of the sphere the link requires lot

of repeaters because of Earth‟s curvature

bull A single satellite can do the magic linking the

continents with one repeater

Motivation to use the Sky

Regions of Space

Space is defined as a place free from obstacles

It can be divided into three regions

bull Air Space -gt region below 100 km from earth‟s surface

bull Outer Space -gt also called cosmic space and ranges from 100 km up till 42 000 km It is mostly used by communication satellites

bull Deep Space -gt Regions beyond 42000 km fall in this category

Satellite

bull It is a repeater which receives signal from

Earth at one frequency amplify it amp

transmit it back to Earth at other

frequency

EARTH STATION

bull There are two earth station in a simple

Satellite communication link One

transmits the signal to satellite called

transmitting Earth station

bull The other receives the signal from

satellite called receiving Earth Station

UPLINK amp DOWN LINK

bull The communication link from

Transmitting earth station to satellite is

called Up-link

bull The communication link from satellite To

receiving earth station is called Down-

link

What is a satellite system

bull A satellite system consists of one or

more satellites a ground-based station to

control the operation of the system and a

user network earth stations that provides

the interface facilities for the transmission

and reception of terrestrial

communications traffic

How a satellite works

bull A satellite stays in orbit because the gravitational

pull of the earth balanced by the centripetal force

of the revolving satellite

bull One Earth station transmits the signals to the

satellite at Up link frequency Up link frequency is

the frequency at which Earth station is

communicating with a satellite

bull The satellite transponder process the signal and

sends it to the second Earth station at another

frequency called downlink frequency

Advantages of Satellite Communications

over Terrestrial Communications

bull The coverage area greatly exceeds

bull Transmission cost of a satellite is independent

of the distance from the center of the coverage

area

bull Satellite-to-satellite communication is very

precise

bull Higher bandwidths are available for use

Disadvantages of Satellite

Communications

bull Launching satellites into orbits is costly

bull Satellite bandwidth is gradually

becoming used up

bull The propagation delay is larger

Active and Passive Satellites

bull Active satellites are used for linking and also for processing the signals

The linkage is known as bent pipe technology where processing like frequency translation power amplification etc take place

Active satellites employ bdquoRegenerative Technology‟ which consists of demodulation processing frequency translation switching and power amplification are carried out Block used for this purpose is called transponder

bull Passive satellites do-not have on-board processing and are just used to link two stations through space

Low cost - Loss of power ndash not useful for communication applications

Historical Overview

bull 1945 Theorist named Clarke studied that satellite orbiting in equatorial orbit

at radius of approx 42000 km would look as if stationary if moving at a

specific speed 3 satellites at a space of 120 degree apart can cover the whole

world Evolution of the concept of GEO

1950rsquos ndashPutting the pieces together

1048708 1956 -Trans-Atlantic cable opened (about 12 telephone channels

per operator)

1048708 1957 First man-made satellite launched by former USSR (Sputnik-

1 LEO) It was used to identify atmospheric density of various orbital

layers It provided data about radio signal distribution in ionosphere

1048708 1958 First US satellite launched (SCORE) First voice

communication established via satellite (LEO lasted 35

days in orbit)

bull 1960rsquos ndashFirst satellite communications

bull 1048708 1960 First passive communication satellite (Large balloons Echo I and II)

bull 1048708 1962 First active communication satellite (Telstar I MEO)

bull 1048708 1963 First satellite into geostationary (GEO) orbit (Syncom1 communication failed)

bull 1048708 1964 International Telecomm Satellite Organization (INTELSAT) created

bull 1048708 1965 First successful communications GEO (Early Bird INTELSAT 1)

Historical Overview

bull 1970rsquos ndashGEO Applications Development DBS

1048708 1972 First domestic satellite system operational (Canada)

1048708 1975 First successful direct broadcast experiment (USA-India)

1048708 1977 A plan for direct broadcast satellites (DBS) assigned by the ITU

1048708 1979 International Mobile Satellite Organization (Inmarsat) established

Historical Overview

bull 1980rsquos ndashGEO Applications Expanded Mobile

1048708 1981 First reusable launch vehicle flight

1048708 1982 International maritime communications made operational

1048708 1984 First direct-to-home broadcast system operational (Japan)

1048708 1987 Successful trials of land-mobile communications (Inmarsat)

1048708 1989-90 Global mobile communication service extended to land mobile and aeronautical use (Inmarsat)

Historical Overview

bull 1990+rsquos NGSO applications development and GEO expansion

1990-95

1048708 Proposals of non-geostationary (NGSO) systems for mobile communications

1048708 Continuing growth of VSATs around the world

1048708 Spectrum allocation for non-GEO systems

1048708 Continuing growth of DBS DirectTV created

1997

1048708 Launch of first batch of LEO for hand-held terminals (Iridium)

1048708 Voice-service portables and paging-service pocket size mobile terminals launched (Inmarsat)

1998-2000

Mobile LEO systems initiate service and fail afterwards (IridiumGlobalstar)

Historical Overview

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Text

bull Course Book

Satellite Communications 4th Edition

Dennis Roddy

Reference Books

1 Satellite Communications 2nd Edition T

Pratt C Bostian and J Allnut

2 Satellite Communications Systems 5th Ed

Gerard Maral Michel Bousquet

Why Satellite Communication

bull The Earth is a sphere amp The microwave frequencies

travel in straight line but to connect two regions very far

away on the two side of the sphere the link requires lot

of repeaters because of Earth‟s curvature

bull A single satellite can do the magic linking the

continents with one repeater

Motivation to use the Sky

Regions of Space

Space is defined as a place free from obstacles

It can be divided into three regions

bull Air Space -gt region below 100 km from earth‟s surface

bull Outer Space -gt also called cosmic space and ranges from 100 km up till 42 000 km It is mostly used by communication satellites

bull Deep Space -gt Regions beyond 42000 km fall in this category

Satellite

bull It is a repeater which receives signal from

Earth at one frequency amplify it amp

transmit it back to Earth at other

frequency

EARTH STATION

bull There are two earth station in a simple

Satellite communication link One

transmits the signal to satellite called

transmitting Earth station

bull The other receives the signal from

satellite called receiving Earth Station

UPLINK amp DOWN LINK

bull The communication link from

Transmitting earth station to satellite is

called Up-link

bull The communication link from satellite To

receiving earth station is called Down-

link

What is a satellite system

bull A satellite system consists of one or

more satellites a ground-based station to

control the operation of the system and a

user network earth stations that provides

the interface facilities for the transmission

and reception of terrestrial

communications traffic

How a satellite works

bull A satellite stays in orbit because the gravitational

pull of the earth balanced by the centripetal force

of the revolving satellite

bull One Earth station transmits the signals to the

satellite at Up link frequency Up link frequency is

the frequency at which Earth station is

communicating with a satellite

bull The satellite transponder process the signal and

sends it to the second Earth station at another

frequency called downlink frequency

Advantages of Satellite Communications

over Terrestrial Communications

bull The coverage area greatly exceeds

bull Transmission cost of a satellite is independent

of the distance from the center of the coverage

area

bull Satellite-to-satellite communication is very

precise

bull Higher bandwidths are available for use

Disadvantages of Satellite

Communications

bull Launching satellites into orbits is costly

bull Satellite bandwidth is gradually

becoming used up

bull The propagation delay is larger

Active and Passive Satellites

bull Active satellites are used for linking and also for processing the signals

The linkage is known as bent pipe technology where processing like frequency translation power amplification etc take place

Active satellites employ bdquoRegenerative Technology‟ which consists of demodulation processing frequency translation switching and power amplification are carried out Block used for this purpose is called transponder

bull Passive satellites do-not have on-board processing and are just used to link two stations through space

Low cost - Loss of power ndash not useful for communication applications

Historical Overview

bull 1945 Theorist named Clarke studied that satellite orbiting in equatorial orbit

at radius of approx 42000 km would look as if stationary if moving at a

specific speed 3 satellites at a space of 120 degree apart can cover the whole

world Evolution of the concept of GEO

1950rsquos ndashPutting the pieces together

1048708 1956 -Trans-Atlantic cable opened (about 12 telephone channels

per operator)

1048708 1957 First man-made satellite launched by former USSR (Sputnik-

1 LEO) It was used to identify atmospheric density of various orbital

layers It provided data about radio signal distribution in ionosphere

1048708 1958 First US satellite launched (SCORE) First voice

communication established via satellite (LEO lasted 35

days in orbit)

bull 1960rsquos ndashFirst satellite communications

bull 1048708 1960 First passive communication satellite (Large balloons Echo I and II)

bull 1048708 1962 First active communication satellite (Telstar I MEO)

bull 1048708 1963 First satellite into geostationary (GEO) orbit (Syncom1 communication failed)

bull 1048708 1964 International Telecomm Satellite Organization (INTELSAT) created

bull 1048708 1965 First successful communications GEO (Early Bird INTELSAT 1)

Historical Overview

bull 1970rsquos ndashGEO Applications Development DBS

1048708 1972 First domestic satellite system operational (Canada)

1048708 1975 First successful direct broadcast experiment (USA-India)

1048708 1977 A plan for direct broadcast satellites (DBS) assigned by the ITU

1048708 1979 International Mobile Satellite Organization (Inmarsat) established

Historical Overview

bull 1980rsquos ndashGEO Applications Expanded Mobile

1048708 1981 First reusable launch vehicle flight

1048708 1982 International maritime communications made operational

1048708 1984 First direct-to-home broadcast system operational (Japan)

1048708 1987 Successful trials of land-mobile communications (Inmarsat)

1048708 1989-90 Global mobile communication service extended to land mobile and aeronautical use (Inmarsat)

Historical Overview

bull 1990+rsquos NGSO applications development and GEO expansion

1990-95

1048708 Proposals of non-geostationary (NGSO) systems for mobile communications

1048708 Continuing growth of VSATs around the world

1048708 Spectrum allocation for non-GEO systems

1048708 Continuing growth of DBS DirectTV created

1997

1048708 Launch of first batch of LEO for hand-held terminals (Iridium)

1048708 Voice-service portables and paging-service pocket size mobile terminals launched (Inmarsat)

1998-2000

Mobile LEO systems initiate service and fail afterwards (IridiumGlobalstar)

Historical Overview

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Why Satellite Communication

bull The Earth is a sphere amp The microwave frequencies

travel in straight line but to connect two regions very far

away on the two side of the sphere the link requires lot

of repeaters because of Earth‟s curvature

bull A single satellite can do the magic linking the

continents with one repeater

Motivation to use the Sky

Regions of Space

Space is defined as a place free from obstacles

It can be divided into three regions

bull Air Space -gt region below 100 km from earth‟s surface

bull Outer Space -gt also called cosmic space and ranges from 100 km up till 42 000 km It is mostly used by communication satellites

bull Deep Space -gt Regions beyond 42000 km fall in this category

Satellite

bull It is a repeater which receives signal from

Earth at one frequency amplify it amp

transmit it back to Earth at other

frequency

EARTH STATION

bull There are two earth station in a simple

Satellite communication link One

transmits the signal to satellite called

transmitting Earth station

bull The other receives the signal from

satellite called receiving Earth Station

UPLINK amp DOWN LINK

bull The communication link from

Transmitting earth station to satellite is

called Up-link

bull The communication link from satellite To

receiving earth station is called Down-

link

What is a satellite system

bull A satellite system consists of one or

more satellites a ground-based station to

control the operation of the system and a

user network earth stations that provides

the interface facilities for the transmission

and reception of terrestrial

communications traffic

How a satellite works

bull A satellite stays in orbit because the gravitational

pull of the earth balanced by the centripetal force

of the revolving satellite

bull One Earth station transmits the signals to the

satellite at Up link frequency Up link frequency is

the frequency at which Earth station is

communicating with a satellite

bull The satellite transponder process the signal and

sends it to the second Earth station at another

frequency called downlink frequency

Advantages of Satellite Communications

over Terrestrial Communications

bull The coverage area greatly exceeds

bull Transmission cost of a satellite is independent

of the distance from the center of the coverage

area

bull Satellite-to-satellite communication is very

precise

bull Higher bandwidths are available for use

Disadvantages of Satellite

Communications

bull Launching satellites into orbits is costly

bull Satellite bandwidth is gradually

becoming used up

bull The propagation delay is larger

Active and Passive Satellites

bull Active satellites are used for linking and also for processing the signals

The linkage is known as bent pipe technology where processing like frequency translation power amplification etc take place

Active satellites employ bdquoRegenerative Technology‟ which consists of demodulation processing frequency translation switching and power amplification are carried out Block used for this purpose is called transponder

bull Passive satellites do-not have on-board processing and are just used to link two stations through space

Low cost - Loss of power ndash not useful for communication applications

Historical Overview

bull 1945 Theorist named Clarke studied that satellite orbiting in equatorial orbit

at radius of approx 42000 km would look as if stationary if moving at a

specific speed 3 satellites at a space of 120 degree apart can cover the whole

world Evolution of the concept of GEO

1950rsquos ndashPutting the pieces together

1048708 1956 -Trans-Atlantic cable opened (about 12 telephone channels

per operator)

1048708 1957 First man-made satellite launched by former USSR (Sputnik-

1 LEO) It was used to identify atmospheric density of various orbital

layers It provided data about radio signal distribution in ionosphere

1048708 1958 First US satellite launched (SCORE) First voice

communication established via satellite (LEO lasted 35

days in orbit)

bull 1960rsquos ndashFirst satellite communications

bull 1048708 1960 First passive communication satellite (Large balloons Echo I and II)

bull 1048708 1962 First active communication satellite (Telstar I MEO)

bull 1048708 1963 First satellite into geostationary (GEO) orbit (Syncom1 communication failed)

bull 1048708 1964 International Telecomm Satellite Organization (INTELSAT) created

bull 1048708 1965 First successful communications GEO (Early Bird INTELSAT 1)

Historical Overview

bull 1970rsquos ndashGEO Applications Development DBS

1048708 1972 First domestic satellite system operational (Canada)

1048708 1975 First successful direct broadcast experiment (USA-India)

1048708 1977 A plan for direct broadcast satellites (DBS) assigned by the ITU

1048708 1979 International Mobile Satellite Organization (Inmarsat) established

Historical Overview

bull 1980rsquos ndashGEO Applications Expanded Mobile

1048708 1981 First reusable launch vehicle flight

1048708 1982 International maritime communications made operational

1048708 1984 First direct-to-home broadcast system operational (Japan)

1048708 1987 Successful trials of land-mobile communications (Inmarsat)

1048708 1989-90 Global mobile communication service extended to land mobile and aeronautical use (Inmarsat)

Historical Overview

bull 1990+rsquos NGSO applications development and GEO expansion

1990-95

1048708 Proposals of non-geostationary (NGSO) systems for mobile communications

1048708 Continuing growth of VSATs around the world

1048708 Spectrum allocation for non-GEO systems

1048708 Continuing growth of DBS DirectTV created

1997

1048708 Launch of first batch of LEO for hand-held terminals (Iridium)

1048708 Voice-service portables and paging-service pocket size mobile terminals launched (Inmarsat)

1998-2000

Mobile LEO systems initiate service and fail afterwards (IridiumGlobalstar)

Historical Overview

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Motivation to use the Sky

Regions of Space

Space is defined as a place free from obstacles

It can be divided into three regions

bull Air Space -gt region below 100 km from earth‟s surface

bull Outer Space -gt also called cosmic space and ranges from 100 km up till 42 000 km It is mostly used by communication satellites

bull Deep Space -gt Regions beyond 42000 km fall in this category

Satellite

bull It is a repeater which receives signal from

Earth at one frequency amplify it amp

transmit it back to Earth at other

frequency

EARTH STATION

bull There are two earth station in a simple

Satellite communication link One

transmits the signal to satellite called

transmitting Earth station

bull The other receives the signal from

satellite called receiving Earth Station

UPLINK amp DOWN LINK

bull The communication link from

Transmitting earth station to satellite is

called Up-link

bull The communication link from satellite To

receiving earth station is called Down-

link

What is a satellite system

bull A satellite system consists of one or

more satellites a ground-based station to

control the operation of the system and a

user network earth stations that provides

the interface facilities for the transmission

and reception of terrestrial

communications traffic

How a satellite works

bull A satellite stays in orbit because the gravitational

pull of the earth balanced by the centripetal force

of the revolving satellite

bull One Earth station transmits the signals to the

satellite at Up link frequency Up link frequency is

the frequency at which Earth station is

communicating with a satellite

bull The satellite transponder process the signal and

sends it to the second Earth station at another

frequency called downlink frequency

Advantages of Satellite Communications

over Terrestrial Communications

bull The coverage area greatly exceeds

bull Transmission cost of a satellite is independent

of the distance from the center of the coverage

area

bull Satellite-to-satellite communication is very

precise

bull Higher bandwidths are available for use

Disadvantages of Satellite

Communications

bull Launching satellites into orbits is costly

bull Satellite bandwidth is gradually

becoming used up

bull The propagation delay is larger

Active and Passive Satellites

bull Active satellites are used for linking and also for processing the signals

The linkage is known as bent pipe technology where processing like frequency translation power amplification etc take place

Active satellites employ bdquoRegenerative Technology‟ which consists of demodulation processing frequency translation switching and power amplification are carried out Block used for this purpose is called transponder

bull Passive satellites do-not have on-board processing and are just used to link two stations through space

Low cost - Loss of power ndash not useful for communication applications

Historical Overview

bull 1945 Theorist named Clarke studied that satellite orbiting in equatorial orbit

at radius of approx 42000 km would look as if stationary if moving at a

specific speed 3 satellites at a space of 120 degree apart can cover the whole

world Evolution of the concept of GEO

1950rsquos ndashPutting the pieces together

1048708 1956 -Trans-Atlantic cable opened (about 12 telephone channels

per operator)

1048708 1957 First man-made satellite launched by former USSR (Sputnik-

1 LEO) It was used to identify atmospheric density of various orbital

layers It provided data about radio signal distribution in ionosphere

1048708 1958 First US satellite launched (SCORE) First voice

communication established via satellite (LEO lasted 35

days in orbit)

bull 1960rsquos ndashFirst satellite communications

bull 1048708 1960 First passive communication satellite (Large balloons Echo I and II)

bull 1048708 1962 First active communication satellite (Telstar I MEO)

bull 1048708 1963 First satellite into geostationary (GEO) orbit (Syncom1 communication failed)

bull 1048708 1964 International Telecomm Satellite Organization (INTELSAT) created

bull 1048708 1965 First successful communications GEO (Early Bird INTELSAT 1)

Historical Overview

bull 1970rsquos ndashGEO Applications Development DBS

1048708 1972 First domestic satellite system operational (Canada)

1048708 1975 First successful direct broadcast experiment (USA-India)

1048708 1977 A plan for direct broadcast satellites (DBS) assigned by the ITU

1048708 1979 International Mobile Satellite Organization (Inmarsat) established

Historical Overview

bull 1980rsquos ndashGEO Applications Expanded Mobile

1048708 1981 First reusable launch vehicle flight

1048708 1982 International maritime communications made operational

1048708 1984 First direct-to-home broadcast system operational (Japan)

1048708 1987 Successful trials of land-mobile communications (Inmarsat)

1048708 1989-90 Global mobile communication service extended to land mobile and aeronautical use (Inmarsat)

Historical Overview

bull 1990+rsquos NGSO applications development and GEO expansion

1990-95

1048708 Proposals of non-geostationary (NGSO) systems for mobile communications

1048708 Continuing growth of VSATs around the world

1048708 Spectrum allocation for non-GEO systems

1048708 Continuing growth of DBS DirectTV created

1997

1048708 Launch of first batch of LEO for hand-held terminals (Iridium)

1048708 Voice-service portables and paging-service pocket size mobile terminals launched (Inmarsat)

1998-2000

Mobile LEO systems initiate service and fail afterwards (IridiumGlobalstar)

Historical Overview

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Regions of Space

Space is defined as a place free from obstacles

It can be divided into three regions

bull Air Space -gt region below 100 km from earth‟s surface

bull Outer Space -gt also called cosmic space and ranges from 100 km up till 42 000 km It is mostly used by communication satellites

bull Deep Space -gt Regions beyond 42000 km fall in this category

Satellite

bull It is a repeater which receives signal from

Earth at one frequency amplify it amp

transmit it back to Earth at other

frequency

EARTH STATION

bull There are two earth station in a simple

Satellite communication link One

transmits the signal to satellite called

transmitting Earth station

bull The other receives the signal from

satellite called receiving Earth Station

UPLINK amp DOWN LINK

bull The communication link from

Transmitting earth station to satellite is

called Up-link

bull The communication link from satellite To

receiving earth station is called Down-

link

What is a satellite system

bull A satellite system consists of one or

more satellites a ground-based station to

control the operation of the system and a

user network earth stations that provides

the interface facilities for the transmission

and reception of terrestrial

communications traffic

How a satellite works

bull A satellite stays in orbit because the gravitational

pull of the earth balanced by the centripetal force

of the revolving satellite

bull One Earth station transmits the signals to the

satellite at Up link frequency Up link frequency is

the frequency at which Earth station is

communicating with a satellite

bull The satellite transponder process the signal and

sends it to the second Earth station at another

frequency called downlink frequency

Advantages of Satellite Communications

over Terrestrial Communications

bull The coverage area greatly exceeds

bull Transmission cost of a satellite is independent

of the distance from the center of the coverage

area

bull Satellite-to-satellite communication is very

precise

bull Higher bandwidths are available for use

Disadvantages of Satellite

Communications

bull Launching satellites into orbits is costly

bull Satellite bandwidth is gradually

becoming used up

bull The propagation delay is larger

Active and Passive Satellites

bull Active satellites are used for linking and also for processing the signals

The linkage is known as bent pipe technology where processing like frequency translation power amplification etc take place

Active satellites employ bdquoRegenerative Technology‟ which consists of demodulation processing frequency translation switching and power amplification are carried out Block used for this purpose is called transponder

bull Passive satellites do-not have on-board processing and are just used to link two stations through space

Low cost - Loss of power ndash not useful for communication applications

Historical Overview

bull 1945 Theorist named Clarke studied that satellite orbiting in equatorial orbit

at radius of approx 42000 km would look as if stationary if moving at a

specific speed 3 satellites at a space of 120 degree apart can cover the whole

world Evolution of the concept of GEO

1950rsquos ndashPutting the pieces together

1048708 1956 -Trans-Atlantic cable opened (about 12 telephone channels

per operator)

1048708 1957 First man-made satellite launched by former USSR (Sputnik-

1 LEO) It was used to identify atmospheric density of various orbital

layers It provided data about radio signal distribution in ionosphere

1048708 1958 First US satellite launched (SCORE) First voice

communication established via satellite (LEO lasted 35

days in orbit)

bull 1960rsquos ndashFirst satellite communications

bull 1048708 1960 First passive communication satellite (Large balloons Echo I and II)

bull 1048708 1962 First active communication satellite (Telstar I MEO)

bull 1048708 1963 First satellite into geostationary (GEO) orbit (Syncom1 communication failed)

bull 1048708 1964 International Telecomm Satellite Organization (INTELSAT) created

bull 1048708 1965 First successful communications GEO (Early Bird INTELSAT 1)

Historical Overview

bull 1970rsquos ndashGEO Applications Development DBS

1048708 1972 First domestic satellite system operational (Canada)

1048708 1975 First successful direct broadcast experiment (USA-India)

1048708 1977 A plan for direct broadcast satellites (DBS) assigned by the ITU

1048708 1979 International Mobile Satellite Organization (Inmarsat) established

Historical Overview

bull 1980rsquos ndashGEO Applications Expanded Mobile

1048708 1981 First reusable launch vehicle flight

1048708 1982 International maritime communications made operational

1048708 1984 First direct-to-home broadcast system operational (Japan)

1048708 1987 Successful trials of land-mobile communications (Inmarsat)

1048708 1989-90 Global mobile communication service extended to land mobile and aeronautical use (Inmarsat)

Historical Overview

bull 1990+rsquos NGSO applications development and GEO expansion

1990-95

1048708 Proposals of non-geostationary (NGSO) systems for mobile communications

1048708 Continuing growth of VSATs around the world

1048708 Spectrum allocation for non-GEO systems

1048708 Continuing growth of DBS DirectTV created

1997

1048708 Launch of first batch of LEO for hand-held terminals (Iridium)

1048708 Voice-service portables and paging-service pocket size mobile terminals launched (Inmarsat)

1998-2000

Mobile LEO systems initiate service and fail afterwards (IridiumGlobalstar)

Historical Overview

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Satellite

bull It is a repeater which receives signal from

Earth at one frequency amplify it amp

transmit it back to Earth at other

frequency

EARTH STATION

bull There are two earth station in a simple

Satellite communication link One

transmits the signal to satellite called

transmitting Earth station

bull The other receives the signal from

satellite called receiving Earth Station

UPLINK amp DOWN LINK

bull The communication link from

Transmitting earth station to satellite is

called Up-link

bull The communication link from satellite To

receiving earth station is called Down-

link

What is a satellite system

bull A satellite system consists of one or

more satellites a ground-based station to

control the operation of the system and a

user network earth stations that provides

the interface facilities for the transmission

and reception of terrestrial

communications traffic

How a satellite works

bull A satellite stays in orbit because the gravitational

pull of the earth balanced by the centripetal force

of the revolving satellite

bull One Earth station transmits the signals to the

satellite at Up link frequency Up link frequency is

the frequency at which Earth station is

communicating with a satellite

bull The satellite transponder process the signal and

sends it to the second Earth station at another

frequency called downlink frequency

Advantages of Satellite Communications

over Terrestrial Communications

bull The coverage area greatly exceeds

bull Transmission cost of a satellite is independent

of the distance from the center of the coverage

area

bull Satellite-to-satellite communication is very

precise

bull Higher bandwidths are available for use

Disadvantages of Satellite

Communications

bull Launching satellites into orbits is costly

bull Satellite bandwidth is gradually

becoming used up

bull The propagation delay is larger

Active and Passive Satellites

bull Active satellites are used for linking and also for processing the signals

The linkage is known as bent pipe technology where processing like frequency translation power amplification etc take place

Active satellites employ bdquoRegenerative Technology‟ which consists of demodulation processing frequency translation switching and power amplification are carried out Block used for this purpose is called transponder

bull Passive satellites do-not have on-board processing and are just used to link two stations through space

Low cost - Loss of power ndash not useful for communication applications

Historical Overview

bull 1945 Theorist named Clarke studied that satellite orbiting in equatorial orbit

at radius of approx 42000 km would look as if stationary if moving at a

specific speed 3 satellites at a space of 120 degree apart can cover the whole

world Evolution of the concept of GEO

1950rsquos ndashPutting the pieces together

1048708 1956 -Trans-Atlantic cable opened (about 12 telephone channels

per operator)

1048708 1957 First man-made satellite launched by former USSR (Sputnik-

1 LEO) It was used to identify atmospheric density of various orbital

layers It provided data about radio signal distribution in ionosphere

1048708 1958 First US satellite launched (SCORE) First voice

communication established via satellite (LEO lasted 35

days in orbit)

bull 1960rsquos ndashFirst satellite communications

bull 1048708 1960 First passive communication satellite (Large balloons Echo I and II)

bull 1048708 1962 First active communication satellite (Telstar I MEO)

bull 1048708 1963 First satellite into geostationary (GEO) orbit (Syncom1 communication failed)

bull 1048708 1964 International Telecomm Satellite Organization (INTELSAT) created

bull 1048708 1965 First successful communications GEO (Early Bird INTELSAT 1)

Historical Overview

bull 1970rsquos ndashGEO Applications Development DBS

1048708 1972 First domestic satellite system operational (Canada)

1048708 1975 First successful direct broadcast experiment (USA-India)

1048708 1977 A plan for direct broadcast satellites (DBS) assigned by the ITU

1048708 1979 International Mobile Satellite Organization (Inmarsat) established

Historical Overview

bull 1980rsquos ndashGEO Applications Expanded Mobile

1048708 1981 First reusable launch vehicle flight

1048708 1982 International maritime communications made operational

1048708 1984 First direct-to-home broadcast system operational (Japan)

1048708 1987 Successful trials of land-mobile communications (Inmarsat)

1048708 1989-90 Global mobile communication service extended to land mobile and aeronautical use (Inmarsat)

Historical Overview

bull 1990+rsquos NGSO applications development and GEO expansion

1990-95

1048708 Proposals of non-geostationary (NGSO) systems for mobile communications

1048708 Continuing growth of VSATs around the world

1048708 Spectrum allocation for non-GEO systems

1048708 Continuing growth of DBS DirectTV created

1997

1048708 Launch of first batch of LEO for hand-held terminals (Iridium)

1048708 Voice-service portables and paging-service pocket size mobile terminals launched (Inmarsat)

1998-2000

Mobile LEO systems initiate service and fail afterwards (IridiumGlobalstar)

Historical Overview

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

EARTH STATION

bull There are two earth station in a simple

Satellite communication link One

transmits the signal to satellite called

transmitting Earth station

bull The other receives the signal from

satellite called receiving Earth Station

UPLINK amp DOWN LINK

bull The communication link from

Transmitting earth station to satellite is

called Up-link

bull The communication link from satellite To

receiving earth station is called Down-

link

What is a satellite system

bull A satellite system consists of one or

more satellites a ground-based station to

control the operation of the system and a

user network earth stations that provides

the interface facilities for the transmission

and reception of terrestrial

communications traffic

How a satellite works

bull A satellite stays in orbit because the gravitational

pull of the earth balanced by the centripetal force

of the revolving satellite

bull One Earth station transmits the signals to the

satellite at Up link frequency Up link frequency is

the frequency at which Earth station is

communicating with a satellite

bull The satellite transponder process the signal and

sends it to the second Earth station at another

frequency called downlink frequency

Advantages of Satellite Communications

over Terrestrial Communications

bull The coverage area greatly exceeds

bull Transmission cost of a satellite is independent

of the distance from the center of the coverage

area

bull Satellite-to-satellite communication is very

precise

bull Higher bandwidths are available for use

Disadvantages of Satellite

Communications

bull Launching satellites into orbits is costly

bull Satellite bandwidth is gradually

becoming used up

bull The propagation delay is larger

Active and Passive Satellites

bull Active satellites are used for linking and also for processing the signals

The linkage is known as bent pipe technology where processing like frequency translation power amplification etc take place

Active satellites employ bdquoRegenerative Technology‟ which consists of demodulation processing frequency translation switching and power amplification are carried out Block used for this purpose is called transponder

bull Passive satellites do-not have on-board processing and are just used to link two stations through space

Low cost - Loss of power ndash not useful for communication applications

Historical Overview

bull 1945 Theorist named Clarke studied that satellite orbiting in equatorial orbit

at radius of approx 42000 km would look as if stationary if moving at a

specific speed 3 satellites at a space of 120 degree apart can cover the whole

world Evolution of the concept of GEO

1950rsquos ndashPutting the pieces together

1048708 1956 -Trans-Atlantic cable opened (about 12 telephone channels

per operator)

1048708 1957 First man-made satellite launched by former USSR (Sputnik-

1 LEO) It was used to identify atmospheric density of various orbital

layers It provided data about radio signal distribution in ionosphere

1048708 1958 First US satellite launched (SCORE) First voice

communication established via satellite (LEO lasted 35

days in orbit)

bull 1960rsquos ndashFirst satellite communications

bull 1048708 1960 First passive communication satellite (Large balloons Echo I and II)

bull 1048708 1962 First active communication satellite (Telstar I MEO)

bull 1048708 1963 First satellite into geostationary (GEO) orbit (Syncom1 communication failed)

bull 1048708 1964 International Telecomm Satellite Organization (INTELSAT) created

bull 1048708 1965 First successful communications GEO (Early Bird INTELSAT 1)

Historical Overview

bull 1970rsquos ndashGEO Applications Development DBS

1048708 1972 First domestic satellite system operational (Canada)

1048708 1975 First successful direct broadcast experiment (USA-India)

1048708 1977 A plan for direct broadcast satellites (DBS) assigned by the ITU

1048708 1979 International Mobile Satellite Organization (Inmarsat) established

Historical Overview

bull 1980rsquos ndashGEO Applications Expanded Mobile

1048708 1981 First reusable launch vehicle flight

1048708 1982 International maritime communications made operational

1048708 1984 First direct-to-home broadcast system operational (Japan)

1048708 1987 Successful trials of land-mobile communications (Inmarsat)

1048708 1989-90 Global mobile communication service extended to land mobile and aeronautical use (Inmarsat)

Historical Overview

bull 1990+rsquos NGSO applications development and GEO expansion

1990-95

1048708 Proposals of non-geostationary (NGSO) systems for mobile communications

1048708 Continuing growth of VSATs around the world

1048708 Spectrum allocation for non-GEO systems

1048708 Continuing growth of DBS DirectTV created

1997

1048708 Launch of first batch of LEO for hand-held terminals (Iridium)

1048708 Voice-service portables and paging-service pocket size mobile terminals launched (Inmarsat)

1998-2000

Mobile LEO systems initiate service and fail afterwards (IridiumGlobalstar)

Historical Overview

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

UPLINK amp DOWN LINK

bull The communication link from

Transmitting earth station to satellite is

called Up-link

bull The communication link from satellite To

receiving earth station is called Down-

link

What is a satellite system

bull A satellite system consists of one or

more satellites a ground-based station to

control the operation of the system and a

user network earth stations that provides

the interface facilities for the transmission

and reception of terrestrial

communications traffic

How a satellite works

bull A satellite stays in orbit because the gravitational

pull of the earth balanced by the centripetal force

of the revolving satellite

bull One Earth station transmits the signals to the

satellite at Up link frequency Up link frequency is

the frequency at which Earth station is

communicating with a satellite

bull The satellite transponder process the signal and

sends it to the second Earth station at another

frequency called downlink frequency

Advantages of Satellite Communications

over Terrestrial Communications

bull The coverage area greatly exceeds

bull Transmission cost of a satellite is independent

of the distance from the center of the coverage

area

bull Satellite-to-satellite communication is very

precise

bull Higher bandwidths are available for use

Disadvantages of Satellite

Communications

bull Launching satellites into orbits is costly

bull Satellite bandwidth is gradually

becoming used up

bull The propagation delay is larger

Active and Passive Satellites

bull Active satellites are used for linking and also for processing the signals

The linkage is known as bent pipe technology where processing like frequency translation power amplification etc take place

Active satellites employ bdquoRegenerative Technology‟ which consists of demodulation processing frequency translation switching and power amplification are carried out Block used for this purpose is called transponder

bull Passive satellites do-not have on-board processing and are just used to link two stations through space

Low cost - Loss of power ndash not useful for communication applications

Historical Overview

bull 1945 Theorist named Clarke studied that satellite orbiting in equatorial orbit

at radius of approx 42000 km would look as if stationary if moving at a

specific speed 3 satellites at a space of 120 degree apart can cover the whole

world Evolution of the concept of GEO

1950rsquos ndashPutting the pieces together

1048708 1956 -Trans-Atlantic cable opened (about 12 telephone channels

per operator)

1048708 1957 First man-made satellite launched by former USSR (Sputnik-

1 LEO) It was used to identify atmospheric density of various orbital

layers It provided data about radio signal distribution in ionosphere

1048708 1958 First US satellite launched (SCORE) First voice

communication established via satellite (LEO lasted 35

days in orbit)

bull 1960rsquos ndashFirst satellite communications

bull 1048708 1960 First passive communication satellite (Large balloons Echo I and II)

bull 1048708 1962 First active communication satellite (Telstar I MEO)

bull 1048708 1963 First satellite into geostationary (GEO) orbit (Syncom1 communication failed)

bull 1048708 1964 International Telecomm Satellite Organization (INTELSAT) created

bull 1048708 1965 First successful communications GEO (Early Bird INTELSAT 1)

Historical Overview

bull 1970rsquos ndashGEO Applications Development DBS

1048708 1972 First domestic satellite system operational (Canada)

1048708 1975 First successful direct broadcast experiment (USA-India)

1048708 1977 A plan for direct broadcast satellites (DBS) assigned by the ITU

1048708 1979 International Mobile Satellite Organization (Inmarsat) established

Historical Overview

bull 1980rsquos ndashGEO Applications Expanded Mobile

1048708 1981 First reusable launch vehicle flight

1048708 1982 International maritime communications made operational

1048708 1984 First direct-to-home broadcast system operational (Japan)

1048708 1987 Successful trials of land-mobile communications (Inmarsat)

1048708 1989-90 Global mobile communication service extended to land mobile and aeronautical use (Inmarsat)

Historical Overview

bull 1990+rsquos NGSO applications development and GEO expansion

1990-95

1048708 Proposals of non-geostationary (NGSO) systems for mobile communications

1048708 Continuing growth of VSATs around the world

1048708 Spectrum allocation for non-GEO systems

1048708 Continuing growth of DBS DirectTV created

1997

1048708 Launch of first batch of LEO for hand-held terminals (Iridium)

1048708 Voice-service portables and paging-service pocket size mobile terminals launched (Inmarsat)

1998-2000

Mobile LEO systems initiate service and fail afterwards (IridiumGlobalstar)

Historical Overview

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

What is a satellite system

bull A satellite system consists of one or

more satellites a ground-based station to

control the operation of the system and a

user network earth stations that provides

the interface facilities for the transmission

and reception of terrestrial

communications traffic

How a satellite works

bull A satellite stays in orbit because the gravitational

pull of the earth balanced by the centripetal force

of the revolving satellite

bull One Earth station transmits the signals to the

satellite at Up link frequency Up link frequency is

the frequency at which Earth station is

communicating with a satellite

bull The satellite transponder process the signal and

sends it to the second Earth station at another

frequency called downlink frequency

Advantages of Satellite Communications

over Terrestrial Communications

bull The coverage area greatly exceeds

bull Transmission cost of a satellite is independent

of the distance from the center of the coverage

area

bull Satellite-to-satellite communication is very

precise

bull Higher bandwidths are available for use

Disadvantages of Satellite

Communications

bull Launching satellites into orbits is costly

bull Satellite bandwidth is gradually

becoming used up

bull The propagation delay is larger

Active and Passive Satellites

bull Active satellites are used for linking and also for processing the signals

The linkage is known as bent pipe technology where processing like frequency translation power amplification etc take place

Active satellites employ bdquoRegenerative Technology‟ which consists of demodulation processing frequency translation switching and power amplification are carried out Block used for this purpose is called transponder

bull Passive satellites do-not have on-board processing and are just used to link two stations through space

Low cost - Loss of power ndash not useful for communication applications

Historical Overview

bull 1945 Theorist named Clarke studied that satellite orbiting in equatorial orbit

at radius of approx 42000 km would look as if stationary if moving at a

specific speed 3 satellites at a space of 120 degree apart can cover the whole

world Evolution of the concept of GEO

1950rsquos ndashPutting the pieces together

1048708 1956 -Trans-Atlantic cable opened (about 12 telephone channels

per operator)

1048708 1957 First man-made satellite launched by former USSR (Sputnik-

1 LEO) It was used to identify atmospheric density of various orbital

layers It provided data about radio signal distribution in ionosphere

1048708 1958 First US satellite launched (SCORE) First voice

communication established via satellite (LEO lasted 35

days in orbit)

bull 1960rsquos ndashFirst satellite communications

bull 1048708 1960 First passive communication satellite (Large balloons Echo I and II)

bull 1048708 1962 First active communication satellite (Telstar I MEO)

bull 1048708 1963 First satellite into geostationary (GEO) orbit (Syncom1 communication failed)

bull 1048708 1964 International Telecomm Satellite Organization (INTELSAT) created

bull 1048708 1965 First successful communications GEO (Early Bird INTELSAT 1)

Historical Overview

bull 1970rsquos ndashGEO Applications Development DBS

1048708 1972 First domestic satellite system operational (Canada)

1048708 1975 First successful direct broadcast experiment (USA-India)

1048708 1977 A plan for direct broadcast satellites (DBS) assigned by the ITU

1048708 1979 International Mobile Satellite Organization (Inmarsat) established

Historical Overview

bull 1980rsquos ndashGEO Applications Expanded Mobile

1048708 1981 First reusable launch vehicle flight

1048708 1982 International maritime communications made operational

1048708 1984 First direct-to-home broadcast system operational (Japan)

1048708 1987 Successful trials of land-mobile communications (Inmarsat)

1048708 1989-90 Global mobile communication service extended to land mobile and aeronautical use (Inmarsat)

Historical Overview

bull 1990+rsquos NGSO applications development and GEO expansion

1990-95

1048708 Proposals of non-geostationary (NGSO) systems for mobile communications

1048708 Continuing growth of VSATs around the world

1048708 Spectrum allocation for non-GEO systems

1048708 Continuing growth of DBS DirectTV created

1997

1048708 Launch of first batch of LEO for hand-held terminals (Iridium)

1048708 Voice-service portables and paging-service pocket size mobile terminals launched (Inmarsat)

1998-2000

Mobile LEO systems initiate service and fail afterwards (IridiumGlobalstar)

Historical Overview

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

How a satellite works

bull A satellite stays in orbit because the gravitational

pull of the earth balanced by the centripetal force

of the revolving satellite

bull One Earth station transmits the signals to the

satellite at Up link frequency Up link frequency is

the frequency at which Earth station is

communicating with a satellite

bull The satellite transponder process the signal and

sends it to the second Earth station at another

frequency called downlink frequency

Advantages of Satellite Communications

over Terrestrial Communications

bull The coverage area greatly exceeds

bull Transmission cost of a satellite is independent

of the distance from the center of the coverage

area

bull Satellite-to-satellite communication is very

precise

bull Higher bandwidths are available for use

Disadvantages of Satellite

Communications

bull Launching satellites into orbits is costly

bull Satellite bandwidth is gradually

becoming used up

bull The propagation delay is larger

Active and Passive Satellites

bull Active satellites are used for linking and also for processing the signals

The linkage is known as bent pipe technology where processing like frequency translation power amplification etc take place

Active satellites employ bdquoRegenerative Technology‟ which consists of demodulation processing frequency translation switching and power amplification are carried out Block used for this purpose is called transponder

bull Passive satellites do-not have on-board processing and are just used to link two stations through space

Low cost - Loss of power ndash not useful for communication applications

Historical Overview

bull 1945 Theorist named Clarke studied that satellite orbiting in equatorial orbit

at radius of approx 42000 km would look as if stationary if moving at a

specific speed 3 satellites at a space of 120 degree apart can cover the whole

world Evolution of the concept of GEO

1950rsquos ndashPutting the pieces together

1048708 1956 -Trans-Atlantic cable opened (about 12 telephone channels

per operator)

1048708 1957 First man-made satellite launched by former USSR (Sputnik-

1 LEO) It was used to identify atmospheric density of various orbital

layers It provided data about radio signal distribution in ionosphere

1048708 1958 First US satellite launched (SCORE) First voice

communication established via satellite (LEO lasted 35

days in orbit)

bull 1960rsquos ndashFirst satellite communications

bull 1048708 1960 First passive communication satellite (Large balloons Echo I and II)

bull 1048708 1962 First active communication satellite (Telstar I MEO)

bull 1048708 1963 First satellite into geostationary (GEO) orbit (Syncom1 communication failed)

bull 1048708 1964 International Telecomm Satellite Organization (INTELSAT) created

bull 1048708 1965 First successful communications GEO (Early Bird INTELSAT 1)

Historical Overview

bull 1970rsquos ndashGEO Applications Development DBS

1048708 1972 First domestic satellite system operational (Canada)

1048708 1975 First successful direct broadcast experiment (USA-India)

1048708 1977 A plan for direct broadcast satellites (DBS) assigned by the ITU

1048708 1979 International Mobile Satellite Organization (Inmarsat) established

Historical Overview

bull 1980rsquos ndashGEO Applications Expanded Mobile

1048708 1981 First reusable launch vehicle flight

1048708 1982 International maritime communications made operational

1048708 1984 First direct-to-home broadcast system operational (Japan)

1048708 1987 Successful trials of land-mobile communications (Inmarsat)

1048708 1989-90 Global mobile communication service extended to land mobile and aeronautical use (Inmarsat)

Historical Overview

bull 1990+rsquos NGSO applications development and GEO expansion

1990-95

1048708 Proposals of non-geostationary (NGSO) systems for mobile communications

1048708 Continuing growth of VSATs around the world

1048708 Spectrum allocation for non-GEO systems

1048708 Continuing growth of DBS DirectTV created

1997

1048708 Launch of first batch of LEO for hand-held terminals (Iridium)

1048708 Voice-service portables and paging-service pocket size mobile terminals launched (Inmarsat)

1998-2000

Mobile LEO systems initiate service and fail afterwards (IridiumGlobalstar)

Historical Overview

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Advantages of Satellite Communications

over Terrestrial Communications

bull The coverage area greatly exceeds

bull Transmission cost of a satellite is independent

of the distance from the center of the coverage

area

bull Satellite-to-satellite communication is very

precise

bull Higher bandwidths are available for use

Disadvantages of Satellite

Communications

bull Launching satellites into orbits is costly

bull Satellite bandwidth is gradually

becoming used up

bull The propagation delay is larger

Active and Passive Satellites

bull Active satellites are used for linking and also for processing the signals

The linkage is known as bent pipe technology where processing like frequency translation power amplification etc take place

Active satellites employ bdquoRegenerative Technology‟ which consists of demodulation processing frequency translation switching and power amplification are carried out Block used for this purpose is called transponder

bull Passive satellites do-not have on-board processing and are just used to link two stations through space

Low cost - Loss of power ndash not useful for communication applications

Historical Overview

bull 1945 Theorist named Clarke studied that satellite orbiting in equatorial orbit

at radius of approx 42000 km would look as if stationary if moving at a

specific speed 3 satellites at a space of 120 degree apart can cover the whole

world Evolution of the concept of GEO

1950rsquos ndashPutting the pieces together

1048708 1956 -Trans-Atlantic cable opened (about 12 telephone channels

per operator)

1048708 1957 First man-made satellite launched by former USSR (Sputnik-

1 LEO) It was used to identify atmospheric density of various orbital

layers It provided data about radio signal distribution in ionosphere

1048708 1958 First US satellite launched (SCORE) First voice

communication established via satellite (LEO lasted 35

days in orbit)

bull 1960rsquos ndashFirst satellite communications

bull 1048708 1960 First passive communication satellite (Large balloons Echo I and II)

bull 1048708 1962 First active communication satellite (Telstar I MEO)

bull 1048708 1963 First satellite into geostationary (GEO) orbit (Syncom1 communication failed)

bull 1048708 1964 International Telecomm Satellite Organization (INTELSAT) created

bull 1048708 1965 First successful communications GEO (Early Bird INTELSAT 1)

Historical Overview

bull 1970rsquos ndashGEO Applications Development DBS

1048708 1972 First domestic satellite system operational (Canada)

1048708 1975 First successful direct broadcast experiment (USA-India)

1048708 1977 A plan for direct broadcast satellites (DBS) assigned by the ITU

1048708 1979 International Mobile Satellite Organization (Inmarsat) established

Historical Overview

bull 1980rsquos ndashGEO Applications Expanded Mobile

1048708 1981 First reusable launch vehicle flight

1048708 1982 International maritime communications made operational

1048708 1984 First direct-to-home broadcast system operational (Japan)

1048708 1987 Successful trials of land-mobile communications (Inmarsat)

1048708 1989-90 Global mobile communication service extended to land mobile and aeronautical use (Inmarsat)

Historical Overview

bull 1990+rsquos NGSO applications development and GEO expansion

1990-95

1048708 Proposals of non-geostationary (NGSO) systems for mobile communications

1048708 Continuing growth of VSATs around the world

1048708 Spectrum allocation for non-GEO systems

1048708 Continuing growth of DBS DirectTV created

1997

1048708 Launch of first batch of LEO for hand-held terminals (Iridium)

1048708 Voice-service portables and paging-service pocket size mobile terminals launched (Inmarsat)

1998-2000

Mobile LEO systems initiate service and fail afterwards (IridiumGlobalstar)

Historical Overview

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Disadvantages of Satellite

Communications

bull Launching satellites into orbits is costly

bull Satellite bandwidth is gradually

becoming used up

bull The propagation delay is larger

Active and Passive Satellites

bull Active satellites are used for linking and also for processing the signals

The linkage is known as bent pipe technology where processing like frequency translation power amplification etc take place

Active satellites employ bdquoRegenerative Technology‟ which consists of demodulation processing frequency translation switching and power amplification are carried out Block used for this purpose is called transponder

bull Passive satellites do-not have on-board processing and are just used to link two stations through space

Low cost - Loss of power ndash not useful for communication applications

Historical Overview

bull 1945 Theorist named Clarke studied that satellite orbiting in equatorial orbit

at radius of approx 42000 km would look as if stationary if moving at a

specific speed 3 satellites at a space of 120 degree apart can cover the whole

world Evolution of the concept of GEO

1950rsquos ndashPutting the pieces together

1048708 1956 -Trans-Atlantic cable opened (about 12 telephone channels

per operator)

1048708 1957 First man-made satellite launched by former USSR (Sputnik-

1 LEO) It was used to identify atmospheric density of various orbital

layers It provided data about radio signal distribution in ionosphere

1048708 1958 First US satellite launched (SCORE) First voice

communication established via satellite (LEO lasted 35

days in orbit)

bull 1960rsquos ndashFirst satellite communications

bull 1048708 1960 First passive communication satellite (Large balloons Echo I and II)

bull 1048708 1962 First active communication satellite (Telstar I MEO)

bull 1048708 1963 First satellite into geostationary (GEO) orbit (Syncom1 communication failed)

bull 1048708 1964 International Telecomm Satellite Organization (INTELSAT) created

bull 1048708 1965 First successful communications GEO (Early Bird INTELSAT 1)

Historical Overview

bull 1970rsquos ndashGEO Applications Development DBS

1048708 1972 First domestic satellite system operational (Canada)

1048708 1975 First successful direct broadcast experiment (USA-India)

1048708 1977 A plan for direct broadcast satellites (DBS) assigned by the ITU

1048708 1979 International Mobile Satellite Organization (Inmarsat) established

Historical Overview

bull 1980rsquos ndashGEO Applications Expanded Mobile

1048708 1981 First reusable launch vehicle flight

1048708 1982 International maritime communications made operational

1048708 1984 First direct-to-home broadcast system operational (Japan)

1048708 1987 Successful trials of land-mobile communications (Inmarsat)

1048708 1989-90 Global mobile communication service extended to land mobile and aeronautical use (Inmarsat)

Historical Overview

bull 1990+rsquos NGSO applications development and GEO expansion

1990-95

1048708 Proposals of non-geostationary (NGSO) systems for mobile communications

1048708 Continuing growth of VSATs around the world

1048708 Spectrum allocation for non-GEO systems

1048708 Continuing growth of DBS DirectTV created

1997

1048708 Launch of first batch of LEO for hand-held terminals (Iridium)

1048708 Voice-service portables and paging-service pocket size mobile terminals launched (Inmarsat)

1998-2000

Mobile LEO systems initiate service and fail afterwards (IridiumGlobalstar)

Historical Overview

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Active and Passive Satellites

bull Active satellites are used for linking and also for processing the signals

The linkage is known as bent pipe technology where processing like frequency translation power amplification etc take place

Active satellites employ bdquoRegenerative Technology‟ which consists of demodulation processing frequency translation switching and power amplification are carried out Block used for this purpose is called transponder

bull Passive satellites do-not have on-board processing and are just used to link two stations through space

Low cost - Loss of power ndash not useful for communication applications

Historical Overview

bull 1945 Theorist named Clarke studied that satellite orbiting in equatorial orbit

at radius of approx 42000 km would look as if stationary if moving at a

specific speed 3 satellites at a space of 120 degree apart can cover the whole

world Evolution of the concept of GEO

1950rsquos ndashPutting the pieces together

1048708 1956 -Trans-Atlantic cable opened (about 12 telephone channels

per operator)

1048708 1957 First man-made satellite launched by former USSR (Sputnik-

1 LEO) It was used to identify atmospheric density of various orbital

layers It provided data about radio signal distribution in ionosphere

1048708 1958 First US satellite launched (SCORE) First voice

communication established via satellite (LEO lasted 35

days in orbit)

bull 1960rsquos ndashFirst satellite communications

bull 1048708 1960 First passive communication satellite (Large balloons Echo I and II)

bull 1048708 1962 First active communication satellite (Telstar I MEO)

bull 1048708 1963 First satellite into geostationary (GEO) orbit (Syncom1 communication failed)

bull 1048708 1964 International Telecomm Satellite Organization (INTELSAT) created

bull 1048708 1965 First successful communications GEO (Early Bird INTELSAT 1)

Historical Overview

bull 1970rsquos ndashGEO Applications Development DBS

1048708 1972 First domestic satellite system operational (Canada)

1048708 1975 First successful direct broadcast experiment (USA-India)

1048708 1977 A plan for direct broadcast satellites (DBS) assigned by the ITU

1048708 1979 International Mobile Satellite Organization (Inmarsat) established

Historical Overview

bull 1980rsquos ndashGEO Applications Expanded Mobile

1048708 1981 First reusable launch vehicle flight

1048708 1982 International maritime communications made operational

1048708 1984 First direct-to-home broadcast system operational (Japan)

1048708 1987 Successful trials of land-mobile communications (Inmarsat)

1048708 1989-90 Global mobile communication service extended to land mobile and aeronautical use (Inmarsat)

Historical Overview

bull 1990+rsquos NGSO applications development and GEO expansion

1990-95

1048708 Proposals of non-geostationary (NGSO) systems for mobile communications

1048708 Continuing growth of VSATs around the world

1048708 Spectrum allocation for non-GEO systems

1048708 Continuing growth of DBS DirectTV created

1997

1048708 Launch of first batch of LEO for hand-held terminals (Iridium)

1048708 Voice-service portables and paging-service pocket size mobile terminals launched (Inmarsat)

1998-2000

Mobile LEO systems initiate service and fail afterwards (IridiumGlobalstar)

Historical Overview

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Historical Overview

bull 1945 Theorist named Clarke studied that satellite orbiting in equatorial orbit

at radius of approx 42000 km would look as if stationary if moving at a

specific speed 3 satellites at a space of 120 degree apart can cover the whole

world Evolution of the concept of GEO

1950rsquos ndashPutting the pieces together

1048708 1956 -Trans-Atlantic cable opened (about 12 telephone channels

per operator)

1048708 1957 First man-made satellite launched by former USSR (Sputnik-

1 LEO) It was used to identify atmospheric density of various orbital

layers It provided data about radio signal distribution in ionosphere

1048708 1958 First US satellite launched (SCORE) First voice

communication established via satellite (LEO lasted 35

days in orbit)

bull 1960rsquos ndashFirst satellite communications

bull 1048708 1960 First passive communication satellite (Large balloons Echo I and II)

bull 1048708 1962 First active communication satellite (Telstar I MEO)

bull 1048708 1963 First satellite into geostationary (GEO) orbit (Syncom1 communication failed)

bull 1048708 1964 International Telecomm Satellite Organization (INTELSAT) created

bull 1048708 1965 First successful communications GEO (Early Bird INTELSAT 1)

Historical Overview

bull 1970rsquos ndashGEO Applications Development DBS

1048708 1972 First domestic satellite system operational (Canada)

1048708 1975 First successful direct broadcast experiment (USA-India)

1048708 1977 A plan for direct broadcast satellites (DBS) assigned by the ITU

1048708 1979 International Mobile Satellite Organization (Inmarsat) established

Historical Overview

bull 1980rsquos ndashGEO Applications Expanded Mobile

1048708 1981 First reusable launch vehicle flight

1048708 1982 International maritime communications made operational

1048708 1984 First direct-to-home broadcast system operational (Japan)

1048708 1987 Successful trials of land-mobile communications (Inmarsat)

1048708 1989-90 Global mobile communication service extended to land mobile and aeronautical use (Inmarsat)

Historical Overview

bull 1990+rsquos NGSO applications development and GEO expansion

1990-95

1048708 Proposals of non-geostationary (NGSO) systems for mobile communications

1048708 Continuing growth of VSATs around the world

1048708 Spectrum allocation for non-GEO systems

1048708 Continuing growth of DBS DirectTV created

1997

1048708 Launch of first batch of LEO for hand-held terminals (Iridium)

1048708 Voice-service portables and paging-service pocket size mobile terminals launched (Inmarsat)

1998-2000

Mobile LEO systems initiate service and fail afterwards (IridiumGlobalstar)

Historical Overview

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

bull 1960rsquos ndashFirst satellite communications

bull 1048708 1960 First passive communication satellite (Large balloons Echo I and II)

bull 1048708 1962 First active communication satellite (Telstar I MEO)

bull 1048708 1963 First satellite into geostationary (GEO) orbit (Syncom1 communication failed)

bull 1048708 1964 International Telecomm Satellite Organization (INTELSAT) created

bull 1048708 1965 First successful communications GEO (Early Bird INTELSAT 1)

Historical Overview

bull 1970rsquos ndashGEO Applications Development DBS

1048708 1972 First domestic satellite system operational (Canada)

1048708 1975 First successful direct broadcast experiment (USA-India)

1048708 1977 A plan for direct broadcast satellites (DBS) assigned by the ITU

1048708 1979 International Mobile Satellite Organization (Inmarsat) established

Historical Overview

bull 1980rsquos ndashGEO Applications Expanded Mobile

1048708 1981 First reusable launch vehicle flight

1048708 1982 International maritime communications made operational

1048708 1984 First direct-to-home broadcast system operational (Japan)

1048708 1987 Successful trials of land-mobile communications (Inmarsat)

1048708 1989-90 Global mobile communication service extended to land mobile and aeronautical use (Inmarsat)

Historical Overview

bull 1990+rsquos NGSO applications development and GEO expansion

1990-95

1048708 Proposals of non-geostationary (NGSO) systems for mobile communications

1048708 Continuing growth of VSATs around the world

1048708 Spectrum allocation for non-GEO systems

1048708 Continuing growth of DBS DirectTV created

1997

1048708 Launch of first batch of LEO for hand-held terminals (Iridium)

1048708 Voice-service portables and paging-service pocket size mobile terminals launched (Inmarsat)

1998-2000

Mobile LEO systems initiate service and fail afterwards (IridiumGlobalstar)

Historical Overview

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

bull 1970rsquos ndashGEO Applications Development DBS

1048708 1972 First domestic satellite system operational (Canada)

1048708 1975 First successful direct broadcast experiment (USA-India)

1048708 1977 A plan for direct broadcast satellites (DBS) assigned by the ITU

1048708 1979 International Mobile Satellite Organization (Inmarsat) established

Historical Overview

bull 1980rsquos ndashGEO Applications Expanded Mobile

1048708 1981 First reusable launch vehicle flight

1048708 1982 International maritime communications made operational

1048708 1984 First direct-to-home broadcast system operational (Japan)

1048708 1987 Successful trials of land-mobile communications (Inmarsat)

1048708 1989-90 Global mobile communication service extended to land mobile and aeronautical use (Inmarsat)

Historical Overview

bull 1990+rsquos NGSO applications development and GEO expansion

1990-95

1048708 Proposals of non-geostationary (NGSO) systems for mobile communications

1048708 Continuing growth of VSATs around the world

1048708 Spectrum allocation for non-GEO systems

1048708 Continuing growth of DBS DirectTV created

1997

1048708 Launch of first batch of LEO for hand-held terminals (Iridium)

1048708 Voice-service portables and paging-service pocket size mobile terminals launched (Inmarsat)

1998-2000

Mobile LEO systems initiate service and fail afterwards (IridiumGlobalstar)

Historical Overview

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

bull 1980rsquos ndashGEO Applications Expanded Mobile

1048708 1981 First reusable launch vehicle flight

1048708 1982 International maritime communications made operational

1048708 1984 First direct-to-home broadcast system operational (Japan)

1048708 1987 Successful trials of land-mobile communications (Inmarsat)

1048708 1989-90 Global mobile communication service extended to land mobile and aeronautical use (Inmarsat)

Historical Overview

bull 1990+rsquos NGSO applications development and GEO expansion

1990-95

1048708 Proposals of non-geostationary (NGSO) systems for mobile communications

1048708 Continuing growth of VSATs around the world

1048708 Spectrum allocation for non-GEO systems

1048708 Continuing growth of DBS DirectTV created

1997

1048708 Launch of first batch of LEO for hand-held terminals (Iridium)

1048708 Voice-service portables and paging-service pocket size mobile terminals launched (Inmarsat)

1998-2000

Mobile LEO systems initiate service and fail afterwards (IridiumGlobalstar)

Historical Overview

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

bull 1990+rsquos NGSO applications development and GEO expansion

1990-95

1048708 Proposals of non-geostationary (NGSO) systems for mobile communications

1048708 Continuing growth of VSATs around the world

1048708 Spectrum allocation for non-GEO systems

1048708 Continuing growth of DBS DirectTV created

1997

1048708 Launch of first batch of LEO for hand-held terminals (Iridium)

1048708 Voice-service portables and paging-service pocket size mobile terminals launched (Inmarsat)

1998-2000

Mobile LEO systems initiate service and fail afterwards (IridiumGlobalstar)

Historical Overview

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Altitudes of orbits above the

earth

bull There are 3 common types of satellite

based on altitude ie GEO MEO amp

LEO

Orbit Altitude Missions possible

Low-Earth orbit LEO 250 to 1500 km

Earth observation

meteorology

telecommunications

(constellations)

Medium-Earth orbit

MEO 10000 to 30000 km

Telecommunications

(constellations)

positioning science

Geostationary Earth

orbit GEO 35786 km

Telecommunications

positioning science

Elliptical orbit Between 800 and

27000 km Telecommunications

Hyperbolic orbit Up to several million

km Interplanetary missions

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

ITU Frequency Spectrum

Allocations

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Communication Satellites

bull Another issue is the presence of the Van Allen belts - layers of highly charged particles trapped by the earths magnetic field

bull Any satellite flying within them would be destroyed fairly quickly by the highly-energetic charged particles trapped there by the earths magnetic field

bull Hence there are three regions in which satellites can be placed safely - illustrated in the following figure

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Communication Satellites

Communication satellites and some of their properties including altitude above the earth round-trip delay time and number of satellites needed for global coverage

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Communication Satellites

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Geostationary Satellites

bull Each downward beam can be focused on a small geographical area so multiple upward and downward transmissions can take place simultaneously

bull Typically the spot beams are elliptically shaped and can be as small as a few hundred km in diameter

bull A communication satellite for the United States typically has one wide beam for the contiguous 48 states plus spot beams for Alaska and Hawaii

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

VSAT systems

bull VSAT (Very Small Aperture Terminal) ndash a satellite communication system that serves home and business users for data voice and video signals

bull Tiny terminals have 1-meter or smaller antennas (versus 10 m for a standard GEO antenna) and can put out about 1 watt of power

bull A VSAT end user has a box that interfaces between the users computer and an outside antenna with a transceiver

bull The tranceiver receives sends a signal to a satellite transponder

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Medium-Earth Orbit Satellites

bull The MEO (Medium-Earth Orbit) satellites are

between the two Van Allen belts

bull Takes something like 6 hours to circle the earth

bull As MEO are lower than the GEOs (typically

16000 km above Earth) they have a smaller

footprint on the ground and require less powerful

transmitters to reach them

bull Currently they are not used for

telecommunications but in navigation systems

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Medium-Earth Orbit Satellites

bull The 24 GPS (Global Positioning System) satellites orbiting at about 18000 km are American but free to use by anyone

bull Russia is using Glonass ndash 24 satellites orbiting at 19100 km

bull European Union works on Galileo ndash 30 satellite MEO navigation system orbiting at 23200 km - global navigation satellite system (GNSS) (2019)

bull China is building Compass ndash 35 satellites ndash 5 GEO and 30 MEO at 21100 km (10 in use and offering services now) (2020)

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Low-Earth Orbit Satellites bull A Low Earth Orbit (LEO) is generally defined as

an orbit below an altitude of approximately 2000

kilometers and above 160 kilometers ndash almost all human

spaceflights have taken place in LEO

bull (-) large numbers of LEO are needed for a complete

system due to their rapid motion (26000 to 27000 km

per hour)

bull (+) satellites are very close to the earth so the ground

stations do not need much power

bull (+) the round-trip delay is only a few milliseconds

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Low-Earth Orbit Satellites

bull Because these LEO orbits are not geostationary a network (or constellation) of satellites is required to provide continuous coverage

bull LEOs are used for a variety of civil scientific and military roles including Earth observation radar optical telecoms and demonstrator

bull Some use as many as 66 satellites (Iridium ndash satellite phones)

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Low-Earth Orbit Satellites

bull The Iridium satellite constellation - group of satellites providing voice and data coverage to satellite phones pagers and integrated transceivers over Earths entire surface

bull Originally developed in 1992 services started in 1998 bankrupted in August 1999 and subsequently restarted in March 2001 (513 000 subscribers in 2011)

bull Satellites are at a height of approximately 781 km bull Customers include the maritime aviation and oil

exploration industries as well as people traveling in parts of the world lacking a telecommunications infrastructure (eg deserts mountains jungles and some Third World countries)

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Iridium

bull The Iridium satellites are in circular polar orbits

bull They are arranged in north-south necklaces with one satellite every 32 degrees of latitude

bull With six satellite necklaces the entire earth is covered

bull Each satellite can support up to 1100 concurrent phone calls and weighs about 680 kg

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Iridium

bull Each satellite has a maximum of 48 cells (spot beams) with a total of 1628 cells over the surface of the earth

bull Each satellite has a capacity of 3840 channels or 253440 in all

bull Some of these are used for paging and navigation while others are used for data and voice

bull An interesting property of Iridium is that communication between distant customers takes place in space with one satellite relaying data to the next one

bull A caller at the North Pole contacts a satellite directly overhead - the call is relayed via other satellites and finally sent down to the called at the South Pole

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Globalstar

bull Globalstar - based on 48 LEO satellites but uses a different switching scheme than that of Iridium (relays calls from satellite to satellite which requires sophisticated switching equipment in the satellites)

bull Globalstar uses a traditional bent-pipe design - a call originating at the North Pole is sent back to earth and picked up by the large ground station

bull The call is then routed via a terrestrial network to the ground station nearest the callee and delivered by a bent-pipe connection as shown

bull Advantage - puts much of the complexity on the ground where it is easier to manage (412300 subscribers in 2010)

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Teledesic

bull Teledesic was as high-speed wireless switched global network -an IP-based system designed to support data voice and video at the same quality level as fiber-based terrestrial systems - a global Internet-in-the-Skyldquo providing broadband and Internet access

bull Originally (1995) planning 840 active satellites with in-orbit spares at an altitude of 700 km

bull Scaled (1997) to 288 active satellites at 1400 km

bull Officially suspended its satellite construction work on October 1 2002

bull Funding from Microsoft (investing US$30 million for an 85 stake) Craig McCaw Bill Gates Paul Allen and Saudi prince Alwaleed bin Talal and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Highly elliptical orbit

bull HEO ndash an elliptic orbit with a low-altitude (about 1000 kilometres) perigee and a high-altitude (over 35786 kilometres) apogee

bull Advantage - long dwell times at a point in the sky during the approach to and descent from apogee - phenomenon known as apogee dwell (acts like GEO) (3-4 hours can receive signal with 06 m antenna)

bull Used by Sirius Satellite Radio (operating in North America) the Molniya communication satelites (at least 3) (Russia)

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Satellite Applications

bull Communication The main application for

satellites today is in communication

Communication satellites act as relay

stations in the sky and permit reliable

long-distance communication worldwide

bull Direct Broadcast Satellite (DBS) service

This is a TV signal distribution system

designed to distribute signals directly to

consumers

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Satellite Applications

bull Satellite Cell Phones Satellite-based

cellular telephone service is under

development The proposed new

systems use low-earth-orbit satellites to

perform the relay services to the main

telephone system or to make connection

directly between any two cellular

telephones using the system

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Satellite Applications

bull Digital Satellite Radio One of the newest satellite applications is in digital satellite radio or the digital audio radio service (DARS)

ndash This service provides hundreds of channels of music news sports and talk radio to car portable and home radios

ndash It provides full continuous coverage of the station you select wherever you are in the United States

ndash Its digital transmission techniques ensure high-quality stereo sound that is immune to noise

ndash The satellites transmit other information such as song title and artist type of music and other data which are displayed on a LCD screen

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Satellite Applications

bull Surveillance satellites can look at the

earth and transmit what they see back to

ground stations for a wide variety of

purposes including military intelligence

meteorological applications and

mapping

bull Satellite navigation systems can provide

global coverage unavailable with land-

based systems satellites

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Global Positioning System

bull The Global Positioning System (GPS) also known as Navstar is a satellite-based navigation system that can be used by anyone with an appropriate receiver to pinpoint his or her location on earth

bull GPS was developed by the US Air Force for the Department of Defense as a continuous global radio navigation system

bull The GPS system consists of three major segments the space segment the control

segment and the user segment

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Global Positioning System

Space Segment

ndash The space segment is the constellation of

satellites orbiting above the earth that

contain transmitters which send highly

accurate timing information to GPS receivers

on earth

bull The GPS consists of 24 main operational satellites

and 3 active spare satellites arranged in six orbits

of 3 or 4 satellites each

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Global Positioning System

Space Segment bull Each of the satellites contains four highly accurate

atomic clocks

bull These clocks are used to generate a unique

pseudorandom code identifying the specific satellite

that is transmitted to earth

bull The satellite also transmits a set of digitally coded

ephemeris data that completely defines its precise

orbit

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Global Positioning System

The GPS space segment

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Global Positioning System

Control Segment

ndash The control segment of the GPS system

refers to the various ground stations that

monitor the satellites and provide control

and update information

bull The master control station is operated by the

US Air Force in Colorado Springs

bull Four additional monitoring and control stations

constantly monitor the satellites and collect range

information from each

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Global Positioning System

Control Segment bull The information is sent back to the master

control station in Colorado where all the

information is collected and position data on

each satellite calculated

bull The master control station then transmits new

ephemeris and clock data to each satellite on the

S-band uplink once per day

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Global Positioning System

GPS Receivers ndash A GPS receiver is a complex superheterodyne

microwave receiver designed to pick up the GPS

signals decode them and then compute the

location of the receiver

ndash The output is usually an LCD display giving latitude

longitude and altitude information andor a map of

the area

ndash The most widely used GPS receiver is the popular

handheld portable type not much larger than an

oversized handheld calculator

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Global Positioning System

GPS Receivers

ndash The receiver performs a time multiplexing

operation on the four satellites within view of

the receiver

ndash The data is extracted from each of the four

satellites and stored in the receiver‟s

memory

ndash Data from three satellites is needed to fix the

receiver‟s position

ndash If data from a fourth satellite is available

altitude can be calculated

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Global Positioning System

GPS receiver

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Global Positioning System

How triangulation works to locate a GPS receiver

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Global Positioning System

GPS Applications

ndash The primary application of the GPS is

military and related navigation

ndash GPS is used by all services for ships

aircraft and ground troops

ndash Most civilian applications also involve

navigation which is usually marine or

aviation-related

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Global Positioning System

GPS Applications

ndash Commercial applications include surveying

mapmaking and construction

ndash Vehicle location is a growing application for trucking

and delivery companies taxi bus and train

transportation

ndash Police fire ambulance and forest services also use

GPS

ndash A new hobby called geocaching uses GPS

receivers In this sport one team hides an item or

ldquotreasurerdquo and then gives the other team

coordinates to follow to find the treasure within a

given time

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Design of the Satellite Link

bull The satellite link is probably the most basic in microwave communications since a line-of-sight path typically exists between the Earth and space

bull This means that an imaginary line extending between the transmitting or receiving Earth station and the satellite antenna passes only through the atmosphere and not ground obstacles

bull Such a link is governed by free-space propagation with only limited variation with respect to time due to various constituents of the atmosphere

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Design of the Satellite Link

bull Free-space attenuation is determined by

the inverse square law which states that the power received is inversely proportional to the square of the distance

bull The same law applies to the amount of light that reaches our eyes from a distant point source such as an automobile headlight or star

bull There are however a number of additional effects that produce a significant amount of degradation and time variation

bull These include rain terrain effects such as absorption by trees and walls and some less-obvious impairment produced by unstable conditions of the air and ionosphere

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest

Design of the Satellite Link

bull It is the job of the communication engineer to identify all of the significant contributions to performance and make sure that they are properly taken into account

bull The required factors include the performance of the satellite itself the configuration and performance of the uplink and downlink Earth stations and the impact of the propagation medium in the frequency band of interest