satellite communications ppt.pptx
TRANSCRIPT
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It is originated fromthe latin word satellit-meaning an attendant,one who is constantlyhovering around andattending to a master
or big man. A heavenly objectwhich revolves aroundsome heavenly body dueto gravitational force. A communication
satellite (COSMAT) is anartificial satellite sent tospace for the purpose oftelecommunications.
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Two stations on earth
want to communicatethrough radio broadcastbut are too far away to useconventional means.
The two stations can use asatellite as a relay station
for their communication.One earth station sends a
transmission to thesatellite. This is calledUPLINK. The satellitetransponder converts thesignal and sends it downto the second earthstation. This is calledDOWNLINK.
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The first artificial satellite
was SOVIET SPUTNIKlaunched on October 4
1957.
The first American satellite
to relay communications wasPROJECT SCORE in 1958.
TELSTAR was the first act
relay 1 launched on Dec 13
1962 and was first to transmit
across pacific.
India launched its first
artificial satellite in 1975.
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Satellites are mainly of twotypes:1.Active satellites
2.Passive satellites
Active satellites: These
satellites have a processing
equipment called
transponder and prevents
interference of signals.
Passive satellites: These are
relay stations in space ,they
include natural satellites
and artificial satellites.
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Based on satellite orbitsGeo stationary earth orbit(GEO) Low earth orbit(LEO)
Medium earth orbit(MEO)
Molniya orbit
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These satellites revolve in a orbit35,863 km above the earths surfacealong the equator. Objects in geostationary orbit revolvearound the earth at the same speed asthe earth revolves. So they are always in
a position relative to earth.GEO orbit is useful for communicationbecause ground antennas can be aimedat the satellite with out having to trackthe satellite motion which is veryinexpensive.
Satellite can not serve extreme northand south areasHeight of the orbitSignificant delay of 0.25 sec incommunications
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LEO satellites are much closer to earth than GEO
satellites ranging from 500 -1500 kms above the earth
surface and correspondingly a period of 90 minutes.
Leo satellites do not stay in a fixed position relative to
earth and are only visible for 15 -20 minutes each pass.
So ,for uninterrupted connectivity a network of LEO
satellites is necessary.
Due to the proximity to the ground, these do notrequire a high signal strength.
A group of satellites working in concert is known as
satellite constellation.Two such constellations intended
to provide satellite phone services to remote areas are
IRIDIUM and GLOBALSTAR systems. Another such wasTELEDESIC.
Discontinuity coverage
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Medium earth orbits(MEO) are at a
distance 2 -8000 kms above the earthssurface.
These satellites have a larger
coverage area than LEO satellites.
A MEO satellite longer duration of
visibility and wider footprint means
fewer satellites are needed in a MEO
network than a LEO network.
A MEO satellite s distance gives it alonger time delay and weaker signal
than a LE0 satellite, though not as bad
as a GEO satellite.
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Used by Russia for decades.This satellites are mainly designed tooperate in the areas of extreme northernand southern latitudes which is the main
drawback of GEO satellites.Molniya orbits are highly inclinedguaranteeing good elevation over selectedpositions during the northern portion ofthe orbit.Period of molniya satellite is half day. so
it is available for operation over the targetfor 6-9 hrs every revolution. So aconstellation of 3 molniya satellites canprovide an uninterrupted coverage.
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TELEPHONE:
The first and historical most important application for
communication satellites was an intercontinental long
distance telephony.
The fixed public switched telephone network
relays telephone calls from land line telephones to
an earth station, where they are then transmitted to a
geostationary satellite. The downlink follows an
analogous path.
With the evolution of fibre optics, the use of satellites
declined but they still serve the remote islands where no
submarine cables are in service.
Satellite phones connect directly to a constellation
either GEO or LEO satellites. calls are then forwarded to
satellite teleport connected to public switch telephone
network.
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Satellite often used as a weapon.A satellite itself neither military norcivil.
1)constellation of military satellites
managed by U.S air force2)provide wideband, narrow bandand protected militarycommunication systems. Wideband: high band width
transfers Protected: more sophisticatedsecurity like nuclear survivability
Narrow band: basic communication
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The advent of HRPT in the 19th
century allowed real time weatherforecasting to become a reality.
Small scale features (mesocyclones,
polar lows) as well as long scale
features (katabatic winds) could be
detected in infrared channel.
1.Lack of high performance
communication links.
2. Development and implementationof software to derive and visualize
products has been lagged.
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1. Payload:
Transponder : Transmit, Receive antennas
other equipments
Receives signals: multiplex, demultiplex , amplify andtransmit.
2. Support Subsystems :
Power Supply, Altitude, orbit control equipment.
Telemetry, Telecommand systems.
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Series of interconnected units
which forms a communication
channel between the receiving
and transmitting antennas.
Transponder is actually
composed of:
1. Input band limiting device
2. An input low noise amplifier
3. Frequency translator4. Output band pass filter
5. Power amplifier
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ADVANTAGES OF COMSAT OVERTERRESTRIAL COMMUNICATION
Coverage area of satellite greatly exceeds than that of
terrestrial system.
Satellite to satellite communication is very precise.
Higher bandwidths available.
Transmission cost of a satellite is independent of the distance
from the center of the coverage area.
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Launching satellite into orbit is
costly.
Satellite band width is graduallybecoming used up.
Failure of satellites during the
equinox period.
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ISRO is amongst the six largest government space agencies inthe world.Indias first satellite ARYABHATA was built by ISRO
First satellite launched by ISRO was SLV3
LAUNCH VEHICLE FLEET:SLV: 4 stage solid fuel light launcher. Intended to reach a
height of 500km.ASLV: 5 stage solid propellent rocket with the capability of
placing 150kg into LEO.
PSLV: 1. design to launch Indian remote sensing satellites.
2. It launched 10 satellites at once, breaking the world record of
Russia.
GSLV:
1.Developed to launch INSAT type vehicles.
2.It is the heaviest satellite launch vehicle of ISRO.
Comparison ofIndian carrierrockets. Left toright: SLV,ASLV,PSLV, GSLV, GSLV
III.
http://en.wikipedia.org/wiki/Satellite_Launch_Vehiclehttp://en.wikipedia.org/wiki/ASLVhttp://en.wikipedia.org/wiki/PSLVhttp://en.wikipedia.org/wiki/GSLVhttp://en.wikipedia.org/wiki/GSLV_IIIhttp://en.wikipedia.org/wiki/GSLV_IIIhttp://en.wikipedia.org/wiki/GSLV_IIIhttp://en.wikipedia.org/wiki/GSLV_IIIhttp://en.wikipedia.org/wiki/GSLVhttp://en.wikipedia.org/wiki/PSLVhttp://en.wikipedia.org/wiki/ASLVhttp://en.wikipedia.org/wiki/Satellite_Launch_Vehicle -
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