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Oct 8, 2015 1Satellite Communications

IntroductionIntroduction

Satellite is a microwave repeater inthe space.

There are about 750 satellites in thespace, most of them are used forcommunication.

They are:Wide area coverage of the earths

surface.

Transmission delay is about 0.!

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Communication SatellitesCommunication Satellites

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How do satellites work?How do satellites work?

Two Stations on "arth want tocommunicate through radio broadcastbut are too far away to use

conventional means.

The two stations can use a satellite as

a relay station for theircommunication.

#ne Earth Station sends atransmission to the satellite. This is

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The satellite Transponder convertsthe signal and sends it down to the

second earth station. This fre$uencyis called a Downlink.

Transponder

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Concept:Conce

pt:

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7/26Oct 8, 2015 7Satellite Communications

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OrbitsOrbits

%ircular orbits are simplest.%ircular orbits are simplest. &nclined orbits are useful for&nclined orbits are useful for

coverage of e$uatorial regionscoverage of e$uatorial regions

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Satellite orbitsSatellite orbits

Classifcation o orbits:

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Satellite orbit altitudesSatellite orbit altitudes

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Ground SegmentGround Segment

The ground Segment of each service The ground Segment of each servicehashas

distinct characteristics.distinct characteristics.

Services li'e(Services li'e( )SS)SS *SS*SS

+SS+SS +aritime, eronautical - and+aritime, eronautical - and

basebase /*S etc../*S etc..

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Service TypesService Types )ied Service Satellites 1)SS2)ied Service Satellites 1)SS2

"ample"ample: 3oint to 3oint %ommunication: 3oint to 3oint %ommunication

*roadcast Service Satellites 1*SS2*roadcast Service Satellites 1*SS2

"ample"ample: Satellite Television4adio: Satellite Television4adio

lso called /irect *roadcast Servicelso called /irect *roadcast Service

1/*S2.1/*S2. +obile Service Satellites 1+SS2+obile Service Satellites 1+SS2

"ample"ample: Satellite 3hones: Satellite 3hones

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Low Earth Orbit (LEO)Low Earth Orbit (LEO)

"# satellites are much closer to the"# satellites are much closer to the

earth than 6"# satellites, ranging fromearth than 6"# satellites, ranging from

500 to ,500 'm above the surface.500 to ,500 'm above the surface.

"# satellites don"# satellites dont stay in 8ed positiont stay in 8ed positionrelative to the surface, and are onlyrelative to the surface, and are only

visible for 5 to 90 minutes each pass.visible for 5 to 90 minutes each pass.

networ' of "# satellites is necessary networ' of "# satellites is necessaryfor "# satellites to be useful.for "# satellites to be useful.

Th I idi t h 66 t llit iTh I idi t h 66 t llit i

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The Iridium system has 66 satellites inThe Iridium system has 66 satellites in

six LEO orbits,six LEO orbits,

each at an altitude of 750 km.each at an altitude of 750 km.

Iridium is designed to provide directworldwide voice and data

communication using handheld

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Advantages:Advantages:

"# satellite "# satellites proimity to earths proimity to earth

compared to a 6"# satellite gives itcompared to a 6"# satellite gives it

a better signal strength and less of aa better signal strength and less of a

time delay, which ma'es it better fortime delay, which ma'es it better forpoint to point communication.point to point communication.

"# satellite "# satellites smaller area ofs smaller area ofcoverage is less of a waste ofcoverage is less of a waste of

bandwidth.bandwidth.

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Disadvantages:Disadvantages: networ' of "# satellites is needed, networ' of "# satellites is needed,

which can be costlywhich can be costly

"# satellites have to compensate for"# satellites have to compensate for

/oppler shifts cause by their relative/oppler shifts cause by their relative

movement.movement.

tmospheric drag eects "#tmospheric drag eects "#satellites, causing gradual orbitalsatellites, causing gradual orbital

deterioration.deterioration.

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edium Earth Orbit (EO)edium Earth Orbit (EO)

+"# satellite is in orbit somewhere +"# satellite is in orbit somewhere

between ;,000 'm and ;,000 'm abovebetween ;,000 'm and ;,000 'm above

the earththe earths surface.s surface.

+"# satellites are similar to "# satellites+"# satellites are similar to "# satellitesin functionality.in functionality.

+"# satellites are visible for much longer+"# satellites are visible for much longer

periods of time than "# satellites, usuallyperiods of time than "# satellites, usually

between 9 to ; hours.between 9 to ; hours. +"# satellites have a larger coverage area+"# satellites have a larger coverage area

than "# satellites.than "# satellites.

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EO satellitesEO satellites

6lonassussian

The 63S

constellationcalls for 9<satellites to be

distributed

http://en.wikipedia.org/wiki/Global_Positioning_Systemhttp://en.wikipedia.org/wiki/Image:GPS_satellite_constellation.jpghttp://en.wikipedia.org/wiki/Global_Positioning_System

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AdvantageAdvantage

= +"# satellite +"# satellites longer duration of visibilitys longer duration of visibilityand wider footprint means fewer satellites areand wider footprint means fewer satellites areneeded in a +"# networ' than a "# networ'needed in a +"# networ' than a "# networ' ..

DisadvantageDisadvantage

= +"# satellite +"# satellites distance gives it a longers distance gives it a longertime delay and wea'er signal than a "#time delay and wea'er signal than a "#

satellite, though not as bad as a 6"# satellitesatellite, though not as bad as a 6"# satellite..

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Geostationar! Earth Orbit (GEO)Geostationar! Earth Orbit (GEO)

These satellites are in orbit !5,;>! These satellites are in orbit !5,;>!

'm above the earth'm above the earths surface alongs surface along

the e$uator.the e$uator.

#b?ects in 6eostationary orbit revolve#b?ects in 6eostationary orbit revolve

around the earth at the same speedaround the earth at the same speed

as the earth rotates. This means 6"#as the earth rotates. This means 6"#

satellites remain in the same positionsatellites remain in the same positionrelative to the surface of earth.relative to the surface of earth.

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Advantages:Advantages: 6"# satellite 6"# satellites distance froms distance from

earth gives it a large coverage area,earth gives it a large coverage area,

almost a fourth of the earthsalmost a fourth of the earths

surface.surface. 6"# satellites have a 9< hour view6"# satellites have a 9< hour view

of a particular area.of a particular area.

These factors ma'e it ideal for These factors ma'e it ideal forsatellite broadcast and othersatellite broadcast and other

multipoint applications.multipoint applications.

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Disadvantages:Disadvantages: 6"# satellite6"# satellites distance also cause it tos distance also cause it to

have both a comparatively wea' signalhave both a comparatively wea' signal

and a time delay in the signal, which isand a time delay in the signal, which isbad for point to point communication.bad for point to point communication.

6"# satellites, centered above the6"# satellites, centered above thee$uator, have di@culty broadcastinge$uator, have di@culty broadcasting

signals to near polar regions.signals to near polar regions.

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Other OrbitsOther Orbits

Molniya Orbit SatellitesMolniya Orbit Satellites

Ased by ussia for decades.Ased by ussia for decades.

+olniya #rbit is an elliptical orbit. The+olniya #rbit is an elliptical orbit. The

satellite remains in a nearly 8edsatellite remains in a nearly 8ed

position relative to earth for eightposition relative to earth for eight

hours.hours.

series of three +olniya satellites can series of three +olniya satellites canact li'e a 6"# satellite.act li'e a 6"# satellite.

Aseful in near polar regionsAseful in near polar regions ..

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olni!a Orbitolni!a Orbit

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High Altitude Platforms HAPs!High Altitude Platforms HAPs!

#ne of the newest ideas in satellite#ne of the newest ideas in satellite

communication.communication. blimp or plane around 90 'm above the blimp or plane around 90 'm above the

earthearths surface is used as a satellite.s surface is used as a satellite. B3s would have very small coverage area,B3s would have very small coverage area,

but would have a comparatively strongbut would have a comparatively strongsignal.signal. %heaper to put in position, but would re$uire%heaper to put in position, but would re$uire

a lot of them in a networ'.a lot of them in a networ'.

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