satellitecommunication final 111014093630 phpapp01

8/13/2019 Satellitecommunication Final 111014093630 Phpapp01

http://slidepdf.com/reader/full/satellitecommunication-final-111014093630-phpapp01 1/47

Satellite Communications

Ppt for Computer Networks



Topics of Presentation

How it

works

Applications

LaunchingHow itworks

FrequencyBands

Intro

Satellites

Types

VSAT

GPS



What are Communication Satellites?

• A satellite is an object that orbits another largeobject like planet.

• A communication satellite is a station in space

that is used for telecommuncation, radio andtelevision signals.

• The first satellite with radio transmitter was in1957.



Need for communication satellite.......

• Early 1950’s and 1960’s,satellite communication bymettallized weather baloons..

•Moon as an artificial satellite.In 1954, the US Naval

Research Laboratory successfully transmitted the first

voice message.

•Disadvantage using moon as a

satellite….Communications via the Moon is limited by

simultaneous visibility of the Moon by both the transmit

and the receive stations

•For further progress,had to wait for an Artificial satellite.



Early Satellites

Syncom• In October 1957, the firstartificial satellite Sputnik -I was

launched.

• 1963 Clark’s idea became a

reality when the first

geosynchronous satellite

SYNCOM was successfully

launched by NASA.

•India launched its first satellite

Aryabhatta on 19 April 1975



Types of Satellites

•In 1950’s both Active and Passive satellites were

used.

• The principle of communication by passive

satellite is based on the properties of scattering of

electromagnetic waves from different surface

areas.

•Thus an electromagnetic wave incident on a

passive satellite is scattered back towards the

earth and a receiving station can receive the

scattered wave.



Active replaces Passive

The disadvantages of passive satellites for

communications are:• The large attenuation of the signal.

• Earth Stations required high power (10 kW) to

transmit signals strong enough to produce an

adequate return echo.• Large Earth Stations with tracking facilities were

expensive.

• A global system would have required a large number

of passive satellites accessed randomly by differentusers

• Control of satellites not possible from ground.



Active satellites

• In active satellites, which amplify andretransmit the signal from the earth have

several advantages over the passive

satellites.

The advantages of active satellites are:

1.Require lower power earth station

2.Less costly

3.Not open to random use4.Directly controlled by operators from ground.



How Does a Satellite Work?

• Consider the light bulb example:



Orbital Options

• A Geosynchronous satellite(GEO)

completes one revolution around the worldevery 23 hrs and 56 minutes in order to

maintain continuous positioning above the

earth’s sub-satellite point on the equator.

• A Medium earth orbit satellite(MEO) requires a constellation

of 10 to 18 satellites in order to maintain

constant coverage of the earth.

•A Low earth orbit satellites(LEO)

offers reduced signal loss since thesesatellites are 20 to 40 times closer to the

earth in their orbits thus allowing for

smaller user terminals/antennas.



Geostationary orbits

• What are they?Geostationary orbits is fixed position to an earth-based observer.

• When was the first use?

The first truly geostationary sateliite was the SYNCOM3 in 1964.

• Why they are important in communications?

- The antennas in the ground don’t need equipment to track the satellite.

- Lower cost & complexity.

• Disadvantages?

- Not always suitable for providing services at high latitudes.

- Molniya satellite was introduced as a solution.



Geostationary Orbit (GEO)

Characteristics of Geostationary(GEO) Orbit System

• User terminals do not have to track the satellite

• Only a few satellites can provide global coverage

• Maximum life-time (15 years or more)

• Above Van Allen Belt Radiation

• Often the lowest cost system and simplest in terms of

tracking and high speed switching.Challenges of Geostationary(GEO) Orbit System

• Transmission latency or delay of 250 millisecond to

complete up/down link

• Satellite antennas must be of larger aperture size toconcentrate power and to create narrower beams for

frequency reuse

• Poor look angle elevations at higher latitudes



Medium Earth Orbit (MEO)

Characteristics of Medium-Earth Orbit system

• Less latency and delay than GEO (but greater than LEO)• Improved look angle to ground receivers in higher latitudes• Fewer satellites to deploy and operate and cheaper TTC&M

systems than LEO (but more expensive than with GEO)• Longer in-orbit lifetime than LEO systems (but less than

GEO)

Challenges of Medium-Earth Orbit System • More satellites to deploy than GEO (10 to 18 vs. 3 to 4)• Ground antennas are generally more expensive and complex

because of the need to track satellites. Or, one must uselower-gain, quasi-omni antennas.

• Increased exposure to Van Allen Belt radiation



Low Earth Orbit (LEO)Characteristics of Low-Earth Orbit (LEO) Systems • Low latency or transmission delay• Higher look angle (especially in high-latituderegions)• Less path loss or beam spreading• Easier to achieve high levels of frequency re-use

• Easier to operate to low-power/low-gain groundantennas.Challenges of Low-Earth Orbit (LEO) Systems • Due to Larger number of satellites (50 to 70satellites). Thus higher launch costs to deploy, build,

and operate.• Harder to deploy, track and operate. There ishigher TTC&M costs even with cross links.• Shorter in-orbit lifetime due to orbital degradation



Properties of Orbits



Satellite-Fiber Comparisoncapability Fiber optic

cable systems

Geo satellite in

a global

system

Meo satellite in

a global

system

Leo satellite in

a global

system

Transmission

speed

10 Gbps-3.2

Terabits/second

Single sat

1Gbps-10Gbps

Single sat

0.5Gbps-5Gbps

Single sat

1Gbps-2Gbps

Quality of

service

10-11 -10-12 10 -6 -10-11 10-6 -10-11 10-2 -1091

Transmission

latency

25 to 50 ms 250 ms 100-150 ms 25-75 ms

System

availability w/o

backup

93 to 99.5% 99.8%(C-Ku

band)

99% (Ka band)

99.9%(C-Ku

band)

99% (Ka band)

99.5%(L-c-Ku

band)

99% (Ka band)

Broadcasting

capabilities

Low to Nil High Low Low

Multi-casting

capabilities

Low High High Medium

Trunking

capabilities

Very High High Medium Low



ELEMENTS OF SATELLITE COMMUNICATIONS

SYSTEM

•Space SegmentSatellite (transponders etc)

Means for launching satellite

Satellite control centre for station keeping of the satellite

•Ground SegmentEarth Stations

Rear Ward Communication links

User terminals and interfaces

Network control centre



Elements



Transponders

•The Transponder (short-for Transmitter-responder ) is the

“BRAIN” of the satellite that provides connection between thesatellite’s Receive and Transmit antennas.

•Satellites can have 12 to 96 transponders plus spares,

depending on the size of the satellite.

•A transponder bandwidth can frequently be 36 MHz, 54 MHz,or 72 MHz or it can be even wider.

•A transponders function is to•Receive the signal, (Signal is one trillion times weaker then when

transmitted)

•Filter out noise,•Shift the frequency to a down link frequency (to avoid interference

w/uplink)

•Amplify for retransmission to ground



Transponder



Satellite Power Systems

• Main source of power is solar cell panels - new solar cells

are increasingly efficient

• The solar cell system is backed up by battery system that provides energy during solar eclipses and other periods ofoutages.

• Typical power levels of 2 to 5 KWs for Fixed SatelliteSystems and 10 to 12 KWs for Mobile and BroadcastSatellite Systems.

Batteries• latest battery technology is represented by Lithium Ion

systems that can provide a greater power density for longer periods of time and survive a greater depth of discharge



Launching Satellites

• How does a satellite stay in it’s orbit?



Launching cntd…

The launch process can be divided into two

phases:

• The Launch Phase

- Satellite placed into the transfer orbit.

• The Orbit Injection Phase

- Satellite transferred from elliptical transfer orbit to

geosynchronous orbit.



Launch Vehicle

• Function-Place the satellite into the desired Orbit.

• Two types

Expandable

• Launch vehicles can be used only once.• Most of the satellite are of this type.

Reusable

• Only one reusable launch vehicle available.



Satellite ejected from the cargo

compartment.

• The Space Shuttle

performs the functions

of the first two stages of

an expendable launch

vehicle.

• The satellite and third

stage assembly are

ejected after reaching

elevation of 150 to 200miles.



Launching contd….

• By riding on a rocket or in the

cargo bay of the SpaceShuttle.

• At about 120 miles (193 km)

up, the rocket's navigational

system fires small rockets, justenough to turn the launch

vehicle into a horizontal

position.

• Inertial guidance system mechanism is used to

calculate adjustments to tilt the

rocket



Path followed by a satellite.



SATELLITE CONTROL CENTRE

Satellite Control Centre performs the following function:-

1. Tracking of the satellite

2. Receiving data

3. Determining Orbital parameters from Tracking and Ranging data

4. Commanding the Satellite for station keeping

5. Switching ON/OFF of different subsystems as per the operationalrequirements

6. Thermal management of satellite.

7. Eclipse management of satellite

8. Communications subsystems configuration management.

9. Satellite Bus subsystems configuration management etc.



CONTROL ROOM



Satellite Frequencies

•There are specific frequency ranges used by commercial

satellites.L-band (Mobile Satellite Services)

1.0 – 2.0 GHz

S-band (MSS, DARS – XM, Sirius)

1.55 – 3.9 GHz

C-band (FSS, VSAT)3.7 – 6.2 GHz

X-Band (Military/Satellite Imagery)

8.0 – 12.0 GHz

Ku-band (FSS, DBS, VSAT)11.7 – 14.5 GHz

Ka-band (FSS “broadband” and inter -satellite

links)

17.7 - 21.2GHz and 27.5 – 31 GHz



Frequency Efficiency

•The vital resource in satellite communications is spectrum.

•As the demand for satellite services has grown, the solution has

been;•To space satellites closer together,

•Allocate new spectrum in higher bands,

•Make satellite transmissions more efficient so that more bits/Hz can be

transmitted, and

•To find ways to re-use allocated spectrum such as through geographicseparation into separated cells or beams or through polarization

separation

•Today the satellites systems transmit more efficiently than ever

before but interference is now a bigger problem - there is a basic

trade off;•The higher the frequency the more spectrum that is available

•But, the higher the frequency the more problems with interference

from other users terrestrial, unlicensed, etc.



VSAT(VERY SMALL APERTURE TERMINALS)

What is VSAT???

• A new development in the communication satelliteworld is the development of low-cost microstations,

sometimes called VSATs.

• These tiny terminals have 1-meter or smaller antennas

(versus 10 m for a standard GEO antenna) and canput out about 1 watt of power .

• In many VSAT systems, the microstations do not have

enough power to communicate directly with one

another (via the satellite, of course). In many VSATsystems, the microstations do not have enough power

to communicate directly with one another (via the

satellite, of course).



Transmission process of VSAT

W ki f VSAT



Working of VSAT

The uplink is generally good for19.2 kbps, but the downlink is

more often 512 kbps or more.

Direct broadcast satellite

television uses this technology

for one-way transmission.

In this mode of operation, either

the sender or the receiver has a

large antenna and a powerful

amplifier. The trade-off is alonger delay in return for having

cheaper end-user stations.

Wh i GPS???



What is GPS???

• The Global Positioning System (GPS)

is a space-based global navigationsatellite system that provides reliable

location and time information in all

weather and at all times and anywhereon or near the Earth when and where

there is an unobstructed line of sight to

four or more GPS satellites.

Gl b l P iti i S t

http://en.wikipedia.org/wiki/Global_navigation_satellite_system


http://en.wikipedia.org/wiki/Positioning_system

http://en.wikipedia.org/wiki/Positioning_system





Global Positioning System

St t



Structure• GPS consists of three parts: the space

segment, the control segment, and the

user segment.

• The U.S. Air Force develops, maintains,

and operates the space and control

segments.

• GPS satellites broadcast signals from

space, which each GPS receiver uses to

calculate its three-dimensional location(latitude, longitude, and altitude) plus the

current time.[1]

St t td

http://en.wikipedia.org/wiki/Broadcast_signal

http://en.wikipedia.org/wiki/Broadcast_signal



Structure contd……

• The space segment is composed of 24 to 32

satellites in medium Earth orbit and also includes theboosters required to launch them into orbit.

• The control segment is composed of a master control

station, an alternate master control station, and a

host of dedicated and shared ground antennas and

monitor stations.

• The user segment is composed of hundreds of

thousands of U.S. and allied military users of the

secure GPS Precise Positioning Service, and tens of

millions of civil, commercial, and scientific users ofthe Standard Positioning Service.

Satellite Network

http://en.wikipedia.org/wiki/Medium_Earth_orbit

http://en.wikipedia.org/wiki/Medium_Earth_orbit



Satellite Network

Branch Offices

Corporate Data

Center/HQ

Network HUB

Corporate Offices

Gas Stations

ApartmentBuildings

Residential

Internet

Some large scale corporate networks

have as many as 10,000 nodes

A li ti



Applications

• Telephony

- Fixed points< earth station> Satellite> earth station> fixed points.

• Televesion & Radio

- e.g. Direct broadcast satellite (DBS) & Fixed service satellite (FFS).

• Mobile satellite technology

- Special antenna called mobile satellite antenna.- No matter where or how this antenna is mounted on.

A li ti



Applications

• Amateur radio

- Access to OSCAR satellite.

- Low earth orbits.

• Internet

- High Speed.

- Useful for far away places.

• Military

- Uses geostationary satellites.

- Example: The Defense Satellite Communications System (DSCS).

Di d t



Disadvantages

• The antenna noise due to energy

- Unwanted radiation sources (stars – galaxies - …etc).

- Worsen S/N ratio.

• Atmosphere behaves as a resistive medium

- Supplies noise power to the antenna.

•Meteors

- Have to be programmed to avoid any rock or any harmful thing.

- Rules of orbits.

• Expensive

- only for governments or large organizations.

I C l i



In Conclusion

Satellites remain the best utilization

used for communications due to their

speed and other advantagesmentioned in this presentation.

satellitecommunication final 111014093630 phpapp01

Documents