Satellite-Communication---1--History-and-Applicati

2011/4/[e-mail]Contents1.Background2.DefinitionsandApplications3.Classification4.History5.MeritsandDrawbacksSection1:Introduction1.BackgroundsSatellitecommunicationsystemshavebecomeanessentialpartoftheworld’stelecommunicationsinfrastructure,servingbillionsofpeoplewithtelephone,dataandvideoservices.Satelliteserviceshaveshiftedawayfromtelephonytowardvideoanddatadelivery,withtelevisionbroadcastingdirectlytothehomeemergingasoneofthemostpowerfulapplications1.BackgroundsRequirementLong-distancecommunicationTelegraphandTelephoneusedcopperwiretocarrysignalsovertheearth’ssurfaceandacrossoceansHighfrequency(HF)radiomadepossibleintercontinentaltelephonelinksArtificialearthsatellitesallowpeopletotalkbytelephoneandexchangeelectronicmailfromanywhereintheworldandtoreceivehundredsofTVchannels1.BackgroundsSatellitecommunicationsystemsexistbecausetheearthisasphereArepeaterneededtoconveysignalsoverlongdistancesbecauseradiowavestravelinstraightlinesatthemicrowavefrequenciesisareceiverlinktoatransmittercanreceiveasignalfromoneearthstation,amplifyitandretransmitittoanotherearthstation1.BackgroundsSatelliteCanlinkplacesontheearthwithlongdistanceIsagoodplacetolocatearepeaterGEOsatelliteisthebestplaceofall2011/4/102OriginalideaArthurC.Clarke,anelectronicengineerandthewell-knownsciencefictionwriterfirstproposedtheconceptofSatelliteCommunications.1945,“ExtraTerrestrialRelays:CanRocketStationsgiveWorldwideRadioCoverage?”publishedinWirelessWorldoutlinedthebasictechnicalconsiderationsinvolvedintheconceptofsatellitecommunications.Proposedorbitingspacestations,whichcouldbeprovidedwithreceivingandtransmittingequipmentandcouldactasarepeatertorelaytransmissionbetweenanytwopointsofthehemispherebeneath.1.Backgrounds1.BackgroundsOriginalideaPointedoutthatthreesuchsynchronousstationslocated120degreesapartabovetheequatorcouldprovideworldwidecommunicationscoverage.Therewerenosatellitesinorbitnorrocketspowerfulenoughtolaunchthem.However,theideasforwhatwenowknowasageostationarysatellitesystemwerenotsciencefiction,whichwasprovedbythefollowinglaunchofthesatellitessuchasSputnik(1957)andEarlyBird(1965).2.DefinitionsandApplicationsDefinitionsSatellite:Anobjectthatrevolvesaroundaplanetinacircularorellipticalpath.ThemoonisEarth'soriginal,naturalsatellite,andtherearemanymanmade(artificial)satellites,usuallyclosertoEarth.Thetermsatelliteistypicallyusedtodescribeausefulobjectplacedinorbitpurposelytoperformsomespecificmissionortask–weathersatellite,communicationsatelliteetc.Satellitecommunications:Intelecommunications,theuseofartificialsatellitestoprovidecommunicationlinksbetweenvariouspointsonEarth.2.DefinitionsandApplicationsCommunicationSatellitecanbelookeduponasalargemicrowaverepeater.Itcontainsseveraltransponderswhichlistenstosomeportionofspectrum,amplifiestheincomingsignalandbroadcastsitinanotherfrequencytoavoidinterferencewithincomingsignals.Motivation:long-distancecommunicationsSatelliteMissionsSource:UnionofConcernedScientists[]SatelliteSystemElements2011/4/103SpaceSegmentSatelliteLaunchingPhaseTransferOrbitPhaseDeploymentOperationTT&C-TrackingTelemetryandCommandStationSSC-SatelliteControlCenter,a.k.a.:•OCC-OperationsControlCenter•SCF-SatelliteControlFacilityRetirementPhaseGroundSegmentCollectionoffacilities,UsersandApplicationsEarthStation=SatelliteCommunicationStation(FixedorMobile)SatelliteUplinkandDownlinkDownlinkThelinkfromasatellitedowntooneormoregroundstationsorreceiversUplinkThelinkfromagroundstationuptoasatellite.Somecompaniesselluplinkanddownlinkservicestotelevisionstations,corporations,andtoothertelecommunicationcarriers.Acompanycanspecializeinprovidinguplinks,downlinks,orboth.SatelliteUplinkandDownlinkSatelliteCommunicationSource:Cryptome[Cryptome.org]Whenusingasatelliteforlongdistancecommunications,thesatelliteactsasarepeater.Anearthstationtransmitsthesignaluptothesatellite(uplink),whichinturnretransmitsittothereceivingearthstation(downlink).Differentfrequenciesareusedforuplink/downlink.2.DefinitionsandApplicationsApplications:UsedtotransmitsignalsanddataoverlongdistancesWeatherforecastingTelevisionbroadcastingInternetcommunicationGlobalPositioningSystems2011/4/1042.DefinitionsandApplicationsDifference–SATCOMandopticalfibercommunicationsTransmissionrate:former-biggestrate4.5Gbps;latter–higherFlexibility:former–onlyneedoneearthterminal;latter–needtopaveopticalcablelocallySatellitecommunicationsfitforcountriescoveringavastterritoryCombineSATCOMandmobilecommunicationstorealizeglobalpersonalcommunicationsTypesofSatelliteOrbitsBasedontheinclination,i,overtheequatorialplane:EquatorialOrbitsaboveEarth’sequator(i=0°)PolarOrbitspassoverbothpoles(i=90°)Otherorbitscalledinclinedorbits(0°i90°)BasedonEccentricityCircularwithcentreattheearth’scentreEllipticalwithonefociatearth’scentre3.ClassificationBasedontheSatelliteAltitudeGEO–GeostationaryEarthOrbits，GEOsatellitescarrythemajorityofservices,duetotheuseofhighgainfi