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Satellite Communication & Networking SATELLITE COMMUNICATION & NETWORKING Submitted By- Sanket Gupta NTPC Electronics & Communication National Thermal Power Corporation Raj Kumar Goel Engg. College INDEX 11.. IInnttrroodduuccttiioonn aa.. HHooww DDoo SSaatteelllliitteess WWoorrkk?? bb.. FFaaccttoorrss IInn SSaatteelllliittee Communication 22.. MMaajjoorr PPrroobblleemmss FFoorr SSaatteelllliitteess aa.. AAddvvaannttaaggeess OOff SSaatteelllliitteess Communication b.b. Disadvantages Of Satellites Communication 33.. TTyyppeess OOff SSaatteelllliitteess aa.. GGeeoossttaattiioonnaarryy EEaarrtthh OOrrbbiitt (GEO) bb.. LLooww EEaarrtthh OOrrbbiitt ((LLEEOO)) cc.. MMeeddiiuumm EEaarrtthh OOrrbbiitt ((MMEEOO)) 44.. FFrreeqquueennccyy BBaannddss OOff SSaatteelllliitteess aa.. SSaatteelllliittee SSeerrvviicceess bb.. FFrreeqquueennccyy BBaannddss 55.. TTeerrmmss UUsseedd IInn SSaatteelllliittee Communication 66.. CCoommppoonneennttss OOff SSaatteelllliittee Communication 7.7. Satellite Communication System 88.. SSaatteelllliittee EEaarrtthh SSttaattiioonn Introduction How Do Satellites Work? If two Stations on Earth want to communicate through rraaddiioo bbrrooaaddccaasstt bbuutt aarree ttoooo ffaarr aawwaayy ttoo uussee coconvnvenentitiononalal memeanans,s, ththenen ththesesee ststatatioionsns cacann ususee aa satellite as a relay station for their communicacommunication.tion. One Earth Station sends a transmission to the satellite. This is called an Uplink . ThThee sasateltellitlitee Transponder earthconverts station. the signalThis is calledand sends a Downlink it down.. to the second Factors In Satellite Communication Elevation Angle: The angle of the horizontal of the eeaarrtthh ssuurrffaaccee ttoo tthhee cceenntteerr lliinnee ooff tthhee ssaatteelllliittee transmission beam. It affects the satellite’s coverage area. CoveraCoveragege AnglAngle:e: A memeasasururee of ththee poportrtioionn of ththee earth surface visible to a satellite taking the minimum elevation angle into account. R/(R + h) = sin(π/2 – β - θ)/sin(θ + π/2) = cos(β + θ)/cos(θ) R = 63637070 km (ea(earthrth’s’s raradiudius),s), h = satsatellelliteite ororbitbit height β = coverage angle, θ = minimum elevation angle MajMajoror ProProbleblemsms F or SatSatellelliteitess Positioning: •• This can be achieved by using small rocket motors and fuel; over half of the weight of most satellites is made up of fuel. •• Commercial life of a satellite typically 10-15 years. Often it is the fuel availability which determines the lifetime of a satellite. Stability: •• It is vital that satellites are stabilised to ensure that ssoollaarr ppaanneellss aanndd ccoommmmuunniiccaattiioonnss aanntteennnnaaee aarree aligned properly. •• Modern satellites use reaction wheel stabilisation, a form of gyroscopic stabilisation. Power: •• Modern satellites use solar panels, so solar power is used to generate efficient electricity. •• Batteries are needed as sometimes the satellites are behind the earth; this happens about half the time for a LEO satellite. Alignment: •• TTheherere araree a nnumumbeberr of cocommpoponnenentsts wwhihichch nneeeedd alignment like Solar panels and Antennae. •• A parabolic dish at antennae can be used which is pointing in the correct general direction. •• DDiiffffeerreenntt ffeeeeddeerr ““hhoorrnnss”” ccaann bbee uusseedd ttoo didirreecctt outgoing and incoming beams more precisely. Harsh Environment: •• SSaatteelllliittee ccoommppoonneennttss nneeeedd ttoo bbee eessppeecciiaallllyy “hardened”. Circuits which work on the ground will fail very rapidly in space. •• TTemempeperaratuturere is alalsoso a prproboblelem,m, so sasatetellllititeses ususee electric heaters to keep circuits and other vital parts warmed up to control the temperature. Atmospheric Attenuation: •• It is caused by air and water that can impair the transmission. •• It is particularly bad during rain and fog. AAddvvaannttaaggeess & DDiissaaddvvaannttaaggeess OOf f Satellites Communication Advantages: •• The coverage area of a satellite greatly exceeds that of a terrestrial system. •• Transmission cost of a satellite is independent of ththee didiststanancece frfromom ththee cecentnterer of ththee cocoveveraragege area. •• SaSattelellilittee ttoo SaSattelelllititee ccomommmuunnicicaattioionn iiss veverryy precise. •• Higher Bandwidths are available for use. Disadvantages: •• Launching satellites into orbit is costly. •• Satellite bandwidth is gradually becoming used up. •• There is a larger propagation delay in satellite ccoommmmuunniiccaattiioonn tthhaann iinn tteerrrreessttrriiaall communication. Types Of Satellites Geostationary Earth Orbit (GEO) TThehesese sasatetellllititeses araree in ororbibitt 3535,8,86363 km aaboboveve ththee eaeartrth’h’ss ssuurfrfaacece aallonongg ththee eqequuatatoorr wiwithth aangnguulalarr sesepapararatitionon ababououtt 2 dedegrgreeees;s; alallolowsws 181800 sasatetellllititeses.. Objects in Geostationary orbit revolve around the earth at the same speed as the earth rotates. This means GEO satellites remain in the same position relative to the surface of earth. Advantages: A GEGEOO sasatetellllitite’e’ss didiststanancece frfromom eaeartrthh gives it a large coverage area, almost a one fourth of the earth’s surface. GEO satellites have a 24 hour view of a papartrticiculularar arareaea.. ThThesesee fafactctororss mamakeke it idideaeall foforr satellite broadcast and other multipoint applicatioapplications.ns. Disadvantages: A GEO satellite’s distance also cause it to have both a comparatively weak signal and a time dedelalayy in ththee sisigngnalal,, whwhicichh is babadd foforr popoinintt to popoinintt cocommmmununicicatatioion.n. GEGEOO sasatetellllititeses,, cecentnterereded ababovovee ththee equequatoator,r, havhavee difdiffificulcultyty in brobroadcadcasastintingg sigsignalnalss neanearr Polar Regions. Low Earth Orbit (LEO) LEO satellites are much closer to the earth than GEO sasatetellllititeses,, rarangnginingg frfromom 505000 to 1,1,505000 km ababovovee ththee susurfrfacace.e. ThThesesee sasatetellllititeses dodon’n’tt ststayay in fifixexedd poposisititionon relative to the surface, and are only visible for 15 to 20 mmininututeess eaeachch papassss.. A nneetwtwororkk ooff LLEOEO ssaatetelllilitetess iiss necessary for LEO satellites to be useful. Advantages: A LELEOO sasatetellllitite’e’ss prproxoximimitityy to eaeartrthh compared to a GEO satellite gives it a better signal strength and less of a time delay, which makes it better foforr popoinintt to popoinintt cocommmmununicicatatioion.n. LELEOO sasatetellllititee hahass smaller area of coverage; less waste of bandwidth. Disadvantages: A nneettwwoorrkk ooff LLEEOO ssaatteelllliitteess iiss neeneededded,, whiwhichch is coscostlytly.. LELEOO sasateltellilitestes hahaveve DoDopplpplerer sshhiiffttss ccaauussee bbyy tthheeiirr rreellaattiivvee mmoovveemmeenntt aanndd atatmmoospsphherericic eeffffeectctss drdraagg LELEOO sasattelelllititeses;; cacauussiningg gradual orbital deterioratideterioration.on. Medium Earth Orbit (MEO) A MEO satellite is in orbit somewhere between 8,000 km anandd 1818,0,00000 km ababovovee ththee eaeartrth’h’ss susurfrfacace.e. MEMEOO satellites are visible for much longer periods of time than LEO satellites, usually between 2 to 8 hours. MEO satellites are similar to LEO satellites in functiofunctionality.nality. Advantages: A MEMEOO sasatetellllitite’e’ss lolongngerer duduraratitionon of visibility and wider footprint, means fewer satellisatellitestes are needed in a MEO network than a LEO network. MEO ssaatteelllliitteess hhaavvee a llaarrgegerr ccoovveerraagege aarreeaa tthhaann LLEEOO satellites. Disadvantages: A MEO satellite’s distance gives it a lloonnggeerr ttiimmee ddeellaayy aanndd wweeaakkeerr ssiigngnaall tthhaann a LLEEOO satellite, though not as bad as a GEO satellitsatellite.e. Frequency Bands Of Satellites Satellite Services Fixed ServServiceice SateSatellitlliteses (FSS) Eg: PoinPointt to Point Communication Broadcast Service Satellites (BSS) Eg: Satellite Television/Radio Mobile Service Satellites (MSS) Eg: Satellite Phones Frequency Bands L–Band: (1 to 2 GHz) used by MSS S-Band: (2 to 4 GHz) used by MSS, NASA, deep space research C-Band: (4 to 8 GHz) used by FSS X-Band: (8 to 12.5 GHz) used by FSS, military and meteorological satellites Ku-Band: (12.5 to 18 GHz) used by FSS and BSS (DBS) K-Band: (18 to 26.5 GHz) used by FSS and BSS Ka-Band: (26.5 to 40 GHz) used by FSS Early Satellite C ommunications used C band iinn rangrangee 3.7 ttoo 44..22 GGHHzz aanndd CCoouulldd iinntteerrffeerree wwiitthh tteerrrreessttrriiaall communications. Its Beam width is narrower with higher frequencies. R ecent Satellite Communications used Ku band mostly. Now Ka band is being used. Terms Used In Satellite Communication Leased Line: It connects two locations for private voice and/or data telecommunication service. It is not a dedicated cable, bubutt acactutualallyly a rereseservrveded cicircrcuiuitt bebetwtweeeenn twtwoo popoinintsts.. LLeeaasseedd lliinneess aarree mmoossttllyy rreenntteedd bbyy bbuussiinneesssseess ttoo connect branch offices, because these lines guarantee babandndwiwidtdthh foforr nenetwtwororkk trtrafaffific.c. TT11 leleasaseded lilineness aarere common and offer good data rate. Dial-up Connection: It is esestatablblisishehedd anandd mamainintatainineded foforr a lilimimitetedd titimeme duduraratitionon.. As an alalteternrnatativive,e, a dededidicacatetedd coconnnnecectitionon continuously takes place. Dial-up lines are also called swswititchcheded lilineness anandd dededidicacatetedd
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