Satellite Communications

Definitionandintroduction

Satellitecommunications:Useartificialearthsatellitesasrelaystationstorelayradiowaves,therebyachievingcommunicationbetweentwoormoreearthstations.

Artificialearthsatellitesareclassifiedintoactiveartificialearthsatellitesandpassiveartificialearthsatellitesaccordingtowhethertheyhavethefunctionofamplifyingradiosignalsandtransmittingfunctions.Sincethesignalsreflectedbypassiveartificialearthsatellitesaretooweaktobeofpracticalvalue,peoplearedevotingthemselvestoresearchonactiveartificialearthsatelliteswithfunctionsofamplification,frequencyconversionandforwarding—communicationssatellitestorealizesatellitecommunication.Amongthem,thegeosynchronoussatellitewhoseperiodoforbitingaroundtheearth'sequatorisequaltotheperiodoftheearth'srotationhassuperiorperformance,andcommunicationusingsynchronoussatelliteshasbecomethemainsatellitecommunicationmethod.Low-orbitsatellitesthatdonotoperateingeosynchronousorbitsaremostlyusedinsatellitemobilecommunications.

Synchronoussatellitecommunicationisacommunicationsatellitethatorbitstheearthinacircularorbitabout36000kmabovetheearth’sequator.Theyarerelativelystationary,sotheyarecalledgeostationarysatellites,fixedsatellitesorgeostationarysatellites,andtheirorbitsarecalledgeosynchronousorbits(GEO).

Communicationscarriedoutonthegroundusingthemicrowaverelaycommunicationsystem,duetoline-of-sightpropagation,onaverageevery2500kmassumingthatthereferencecircuitpasses54relaytransfersperspanofapproximately46km.Ifthecommunicationsatelliteisusedforrelay,thecommunicationwithagrounddistanceofmorethan10,000kilometerscanbeconnectedbyonehopthroughthecommunicationsatellite(fromthegroundtothesatellite,andthenfromthesatellitetothegroundisonehop,includingtworelays),andTherelaydistanceofradiowavetransmissionisabout40,000kilometers,asshowninFigure1.

Abriefhistory

TheideaofusingartificialearthsatellitesingeosynchronousorbitsasrelaystationsforcommunicationontheearthisbasedontheBritishphysicistACClarke(ArtherC.Itwasproposedinthearticle"Extra-EarthRelay"publishedintheWorldMagazine,anditbecamearealityinthe1960s.

Beforetheadventofsynchronoussatellites,variouslow-orbitsatelliteswereusedforscientificexperimentsandcommunications.Theworld'sfirstartificialsatellite"Satellite1"wassuccessfullylaunchedbytheSovietUniononOctober4,1957andorbitedtheearth.Theearthreceivedradiowavesfromanartificialsatelliteforthefirsttime.

InAugust1960,theUnitedStateslaunchedthealuminum-coatedballoonsatellite"Echo1"withadiameterof30mintoacircularorbitabout1600kminheightforcommunicationexperiments.Thisistheworld'searliestso-calledpassiverelaytestwithoutusinganamplifier.

TheUnitedStateslaunchedthelow-orbitsatellite"Relay1"onFebruary13,1962.OnNovember23,1963,thestarachievedthefirsttelevisionbroadcastacrossthePacificbetweenJapanandtheUnitedStates.Atthistime,itcoincidedwiththeassassinationofUSPresidentJ.F.Kennedy.ThenewswastransmittedtoJapanviasatelliteandbroadcastonTVnews.Thelong-distancereal-timetransmissionofsatellitesleftadeepimpressiononpeopleandgreatlyimprovedthestatusofartificialsatellitesincommunications.

Theworld’sfirstsynchronouscommunicationssatellitewasthe"Synchronous2"satellitelaunchedbyNASAinJuly1963.Ithasaninclinationangleof30°totheequatorialplaneandmovesinafigureofeightrelativetotheground.Therefore,itcannotbecalledageostationarysatellite,anditisusedforcommunicationservicesforthefirsttimeintheAtlanticOcean.The"Synchronous3"satellitelaunchedinAugust1964wasfixedneartheinternationaldatelineoverthePacificequatorandwastheworld'sfirstgeostationarysatellite.InOctober1964,thelivebroadcastofthe(Tokyo)OlympicGameswasbroadcastbythestar.Sofar,satellitecommunicationisstillintheexperimentalstage.OnApril6,1965,thefirstsemi-experimentalandsemi-practicalgeostationarysatellite"MorningBird"waslaunchedforcommercialsatellitecommunicationsbetweenEuropeandtheUnitedStates.Sincethen,satellitecommunicationshaveenteredapracticalstage.

Coverage

GeostationaryEarthOrbit(GEO)Satellite

GlobalcoverageofGeostationaryEarthOrbit(GEO)satelliteforfixedsatellitecommunicationsservices,withanorbitheightofapproximately36000km,inacircularorbit,aslongasthreeuniformlydistributedsatellitesseparatedby120°cancoverthewholeworld.TheIntelsatI-IXgenerationsatelliteoftheInternationalSatelliteCommunicationsOrganization.Itisthebestexampleofglobalcoverage,whichhasbeendevelopedtotheninthgeneration.

Thesatelliteactsasarelaystationintheair,thatis,amplifyingtheelectromagneticwavesentfromtheearthstationandthensendingitbacktoanotherearthstation.Theearthstationisthelinkformedbythesatellitesystem.Sincethegeostationarysatelliteis36,000kilometersabovetheequator,itstimetoorbittheearthexactlycoincideswiththerotationoftheearth(23hours,56minutes,4seconds),anditlooksasifitisstationaryfromtheground.Threesatellitesseparatedby120degreescancovertheentireequatorialcircumference.Therefore,satellitecommunicationiseasytorealizetransoceanicandintercontinentalcommunication.Themostsuitablefrequencyforsatellitecommunicationisthe1-10GHzfrequencyband,thatis,themicrowavefrequencyband.Inordertomeetmoreandmoredemands,newfrequencybandshavebeenstudiedandapplied,suchas12GHz,14GHz,20GHzand30GHz.

Mobilesatellitecommunications

Inmarsat,aglobalmobilesatellitecommunicationssystem,isamobilesatellitecommunicationssystemwithglobalcoverage.Itoperatesthird-generationmaritimecommunicationssatellites,whicharedistributedintheAtlanticOcean.Intheeasternandwesternregions,theIndianOceanandthePacificregions,thefourth-generationInmarsat-4satelliteshavelaunchedtheirfirstsatelliteinMarch2005,andanothersatelliteisalsoreadytobelaunched.Theyarefixedat64respectively.Eand53.W,withaglobalbeam,19widespotbeams,228narrowspotbeams,usingadigitalsignalprocessor.Therearechannelselectionandbeamformingfunctions.

Thelow-orbitmobilecommunicationsatelliteswithglobalcoverageinclude"Iridium"andGlobalstar.The"Iridium"systemhas66stars,dividedinto6orbits,eachofwhichhas11Thesatelliteshaveanorbitalheightof765km.Thelinksbetweenthesatellites,betweenthesatellitesandthegatewayandthesystemcontrolcenterusethekaband,andthelinksbetweenthesatelliteandtheuserusetheL-band.AttheendofJune2005,thenumberofIridiumsatelliteusersreached127,000.DuringthedisasterofHurricaneKatrina,theservicetrafficofIridiumsatelliteincreasedby30times,andthesatellitephonecommunicationvolumeincreasedby5times.

Globalstariscomposedof48satellites,distributedin8circularinclinedorbitplanes,withanorbitheightof1389kmandaninclinationangleof52degrees.Thenumberofusershassteadilyincreasedyearbyyear,andthecosthasdecreased.In2005,thenumberofvoiceusersincreasedcomparedwith2004.

Multipleaccessmethod

Multipleaccessmeansthatthesamesatellitetranspondercanbeconnectedtomultipleearthstations.Multipleaccesstechnologydividesthesignalandrecognizesthesignalaccordingtothecharacteristicsofthesignal.,Thesignalusuallyhasthecharacteristicsoffrequency,time,spaceandsoon.Commonlyusedmultipleaccessmethodsforsatellitecommunicationsincludefrequencydivisionmultipleaccess(FDMA),timedivisionmultipleaccess(TDMA),codedivisionmultipleaccess(CDMA)andspacedivisionmultipleaccess(SDMA).Inaddition,frequencyreusetechnologyisalsoItisamultipleaccessmethod.

Inthemicrowavefrequencyband,theworkingfrequencybandoftheentirecommunicationsatellitehasawidthofabout500MHz.Inordertofacilitateamplificationandtransmissionandreducemodulationinterference,severaltranspondersaregenerallyinstalledonthesatellite.Satellitecommunicationswithaworkingfrequencybandwidthof36MHzor72MHzforeachtranspondermostlyusefrequencydivisionmultipleaccesstechnology.Differentearthstationsoccupydifferentfrequencies,thatis,differentcarriersareused.Itismoresuitableforpoint-to-pointlarge-capacitycommunication.Timedivisionmultipleaccesstechnologyhasbeengraduallyadopted,thatis,eachearthstationoccupiesthesamefrequencybandbutdifferenttimeslots.Comparedwithfrequencydivisionmultipleaccess,ithasaseriesofadvantages.Thestationsignalsareseparated,suitablefordigitalcommunication,andcanbeallocatedondemandaccordingtochangesinbusinessvolume.Newtechnologiessuchasdigitalvoiceplug-incanbeusedtoincreasethecapacityby5times.Anothermultipleaccesstechnologymakescodedivisionmultipleaccess(CDMA),thatis,differentearthstationsoccupythesamefrequencyandthesametime,buthavedifferentrandomcodestodistinguishdifferentaddresses.Itadoptsspreadspectrumcommunicationtechnology,hastheadvantagesofstronganti-interferenceability,betterconfidentialcommunicationability,andflexiblevoicechannelscheduling.Itsshortcomingsmakethespectrumutilizationratelow.Itismoresuitableforsystemswithsmallcapacity,widedistribution,andcertainconfidentialityrequirements.

Thecompositionofthesatellitecommunicationsystem

Thesatellitecommunicationsystemincludesalltheequipmentforcommunicationandguaranteeingcommunication.Generally,itconsistsoffourparts:spacesubsystem,communicationearthstation,trackingtelemetryandcommandsubsystem,andmonitoringmanagementsubsystem,asshowninthefigure.

1.Trackingtelemetryandcommandsubsystem

Thetrackingtelemetryandcommandsubsystemisresponsiblefortrackingandmeasuringsatellitesandcontrollingthemtoaccuratelyenterthedesignatedpositiononthegeostationaryorbit.Afterthesatelliteisinnormaloperation,theorbitpositioncorrectionandattitudemaintenanceofthesatelliteshouldbecarriedoutonaregularbasis.

2.Monitoringandmanagementsub-system

Themonitoringandmanagementsub-systemisresponsibleforthedetectionandcontrolofthecommunicationperformanceofthefixed-pointsatellitebeforeandaftertheserviceisopened,suchasthepowerofthesatellitetransponder,thegainofthesatelliteantenna,andthepowertransmittedbyeachearthstationThebasiccommunicationparameterssuchasradiofrequencyandbandwidtharemonitoredtoensurenormalcommunication.

3.Spacesubsystem(communicationsatellite)

Communicationsatellitesmainlyincludecommunicationsystems,telemetrycommanddevices,controlsystems,andpowersupplydevices(includingsolarcellsandstoragebatteries).

Thecommunicationsystemisthemainbodyofthecommunicationsatellite.Itmainlyincludesoneormoretransponders.Eachtranspondercanreceiveandforwardsignalsfrommultipleearthstationsatthesametime,thusactingasarelaystation.

4.Communicationearthstation

Thecommunicationearthstationisamicrowaveradioreceivingandtransmittingstationthroughwhichusersaccesssatellitelinesforcommunication.

Introductiontofrequencybandsynchronoussatellitecommunicationservice

Thefrequencybandsynchronoussatellitecommunicationserviceisdividedintofixedsatellitecommunicationservice(FSS)andsatellitemobilecommunicationservice(MSS).Thefrequencybandsallocatedtothemarealsodifferent.FSSusesC-bandandKu-band.MSSusestheLfrequencyband(seesynchronoussatellitemobilecommunications),andmostoftheKutranspondersworkingintheKufrequencybandareoriginallyspotbeams.Sincethe1990s,theKustaroftheInternationalTelecommunicationsSatelliteOrganization(INTELSAT,abbreviatedasIS)iscalledISK,whichprovidesawiderrangeofservices.Regionalbeamstomeetdemand.ThefrequencydivisionsoftheCandKubandsofFSSareasfollows(theupperlineisthefrequencyusedbytheearthstationtothesatellite,andthelowerlineisthefrequencyusedbythesatellitetotheearthstation).

①Cband(MHz)

Upstream5925～6425Bandwidth500MHz

Downstream3700～4200Bandwidth500MHz

FortheextensionofFSSThefrequencyspectrumhasbeenadjustedfromJanuary1,1984to:

Upstream:Area15725～7075Bandwidth1350MHz

Area2and35850～7075Bandwidth1225MHz

3400～4200totalbandwidth

Downlink:Zone1,2,and3

4500～4800l100MHz

②Kufrequencyband(GHz)

4500～4800l100MHz

Uplink:Zone1,2,and3,14.0～14.25Bandwidth250MHz

14.25～14.5,Bandwidth250MHz

Downlink:Zone1,2,and310.95～11.20Bandwidth250MHz

11.45～11.7Bandwidth250MHz

Section211.7～11.95Bandwidth250MHz

11.95～12.2Bandwidth250MHz

No.3Zone12.2～12.5Bandwidth300MHz

Thefirstandthirdzones12.5～12.75Bandwidth250MHz

Accordingtothefrequencyallocationofthe1992InternationalAdministrativeRadioConference(WARC-92),theInternationalTelecommunicationsSatelliteOrganizationThenewlyallocated13.75～14.0GHz(uplink)withabandwidthof250MHzcanbeusedonJanuary1,2000tomeettheneedsofdevelopment.

ThetransmissionofC-bandisrelativelystable,andtheequipmenttechnologyismature,butitiseasytointerferewiththegroundmicrowavesystemofthesamefrequencyband.Theuplinkofsatellitecommunicationinterfereswiththe6GHzmicrowavesystem,andthedownlinkisinterferedbythe4GHzmicrowavesystem.Thisrequirespre-coordinationandcorrespondingshieldingmeasurestosolveit(seesatellitecommunicationsysteminterferencecoordination).TheKubandtransmissionisattenuatedbyrainandfog.,NotasstableastheC-band,especiallyinareaswithheavyrainfall.Ifsufficientmarginisleftinthecalculationoftheuplinkanddownlink,andtheuplinkpoweradjustmentfunctionisequipped,satisfactoryresultscanalsobeobtained.TheKufrequencybandhasabundantspectrumresourcesandhaslittlemutualinterferencewithterrestrialmicrowavesystems,anditsapplicationisverypromising.

Attheendofthe20thcenturyorthebeginningofthe21stcentury,theCandKufrequencybandswillbecrowded.FSSwilldevelopservicesintheKafrequencybandfrom20GHzto30GHz.Thefrequencyis:

Uplink(GHz)29.5～30Bandwidth500MHz

Downlink(GHz)19.7～20.2Bandwidth500MHz

Satellitecommunicationmethod

SatellitecommunicationmethodThesatellitecommunicationsystemuseswhentransmittingordistributinginformationTheworkingmethodiscalledsatellitecommunicationmethod.

Internationalsatellitecommunicationshaveshiftedfrombeingbasedonanalogfrequencydivisiontodigitaltimedivision.Digitalsatellitecommunicationmethodsinclude120Mbit/sdigitalvoiceinsertion(DSI)timedivisionmultipleaccess(TDMA/DSI),ortimedivisionmultipleaccesswithoutvoiceinsertion(DNI),andon-boardswitchingtimedivisionmultipleaccess(SS-TDMA);Therearealsoalargenumberofsatellitedigitalchannel(IDR)methodsbasedon2.048Mbit/sand1.544Mbit/s.Addingdigitalcircuitmultiplexingequipment(DCME)cangenerallyexpandthecapacityby3to4times,upto5times.The2Mbit/sIDRbears30circuits,andthesmallercapacityIDRhas1.024Mbit/s(16circuits)and512kbit/s(8circuits).Thedigitalprivatelineservice(IBS)fordedicatedcommunicationshasdevelopedrapidly,andtheKu-bandreachingtheISDNqualityleveliscalledthesuperdigitalprivatelineservice(su-perIBS).Thereisstillamarketforthesparserouting(VISTA)businessmode,amongwhichthereisamodeofon-demandallocationofmultipleaccess(DAMA)functionscalledthesuperthinrouting(su-perVISTA)mode.TheSPADEmethodofnon-centrallycontrolledrareroutinghasbeeneliminatedduetocomplexequipment.Thepolarizationmodeofinternationalsatellitecommunicationsisdoublecircularpolarization.

DomesticsatellitecommunicationmethodsgenerallyimitatetheC-bandandKu-bandusedbyinternationalsatellitecommunications,andKa-bandisalsouseful.ThegeneralTDMAmethodisbelow60Mbit/s,andthereareSS-TDMAandtransponderfrequencyhoppingTDMAmethods,satellitedigitalchannel(IDR/DCME)methodswithdigitalcircuitmultiplexingequipment,andadaptivedifferentialpulsecodingSatellitedigitalchannel(IDR/ADPCM)mode.Becausetheanalogfrequencydivisionmultipleaccess(FDMA)technologyismature,itisstillinuse.Thecall-basedsparserouting(VISTA)methodisusedmoreinthecountry,includingsinglecarriersinglechannel/syllabiccompandingfrequencymodulation/on-demandmultipleaccess(SCPC/CFM/DAMA)methodandsinglecarriersinglechannel/4phaseshiftkeying/on-demandmultipleaccess(SCPC/QPSK/DAMA)modeandlowerrateTDMAmode.Themarketforverysmallantennaearthstationsystemsisverylarge.Itisastarnetworkwithdatatransmissionasthemainpartandvoicetransmission.Therearemanyformatsandspeedsforuserstochoosefrom.Thepolarizationmodeofdomesticsatellitecommunicationisgenerallylinearpolarization,andcircularpolarizationisalsousedinsomecases.

InternationalanddomesticsatelliteTVtransmissionadoptsanalogFMsystem.TheinternationalTVprogramexchangeusestheglobalbeamtransponderandtheAstandardearthstation,anditsreceptionqualityisbetter.Onetranspondercantransmittwochannelsof20MHzbandwidthTVprograms.DomesticandregionalsatelliteTVtransmissionsuseadomesticorregionalbeamtranspondertoturnononlyoneTV,andtakethefullpowerofthetransponder,sothatalargenumberofsmallTVsingle-receivingearthstationsareeasytoreceive.

Thecompositeanalogcomponent(MAC)systemisalsoinuse.Atwo-channelTVsysteminwhichtwochannelsofTVaretransmittedbyonecarrierisusedasafixed-pointTVprogramtransmissionmethod,whichcansavespacesectioncosts,soitisalsoadopted.High-qualitysatellitedigitalTVtransmissionandhigh-resolutionsatelliteTVtransmissionarebeingtested.AtranspondertransmissionmethodofdigitalTVwithmultiplecompressioncodingisabouttoappear.

Thesatellitevideoteleconferencebusinessismainlybasedon2Mbit/1.5Mbit.Then×384kbiversionhasalreadycomeout,anditisexpectedthatthem×64kbitversionwillalsohaveitsadvantages.

ThesmallC/Kuearthstation,whichisinstalledonaspecialvehicleandiseasytocarry,iswidelyusedinvariousdomesticandinternationaloccasions.ItcanbeusedtotransmitTV,telephone,fax,telegraphanddata,etc.,Mostlyusedinemergencysituations.

Features

Comparedwithothercommunicationmethods,satellitecommunicationhasthefollowingcharacteristics:

①Thecommunicationdistanceislong,andthecosthasnothingtodowiththecommunicationdistance..ItcanbeseenfromFigure16.2thatusinggeostationarysatellites,themaximumcommunicationdistanceisabout18100km.Moreover,theconstructioncostandoperatingcostdonotchangeduetothedistancebetweenthecommunicationstationsandtheharshnaturalconditionsonthegroundbetweenthetwocommunicationstations.Thishasobviousadvantagesovermicrowaverelay,cables,opticalcables,andshort-wavecommunicationsinlong-distancecommunications.

②Itworksinbroadcastmodeandcancarryoutmulti-addresscommunication.Generally,othertypesofcommunicationmethodscanonlyachievepoint-to-pointcommunication,whilesatellitesworkinbroadcastmode.Anearthstationcanbesetupatanypointintheentireareacoveredbythesatelliteantennabeam,andtheseearthstationscanshareacommunicationsatellite.Toachievebilateralormultilateralcommunication,thatis,multiple-accesscommunication.Inaddition,anin-orbitsatelliteisequivalenttolayingcountlessinvisiblecircuitsthatcanreachanypointinacertainarea.Itprovideshighefficiencyandflexibilityforthecompositionofthecommunicationnetwork.

③Largecommunicationcapacity,suitableforavarietyofbusinesstransmission.Satellitecommunicationsusemicrowavefrequencybands,andtheusablefrequencybandsareverywide.Generally,thesatellitebandwidthoftheCandKubandscanreach500-800MHz,andtheKabandcanreachseveralGHz.

④Itcanbemonitoredspontaneously.Generally,thesenderearthstationcanalsoreceivethesignalsentbyitself,sothatitcanmonitorwhetherthemessagesentbythestationiscorrectandthequalityofthetransmission.

⑤Seamlesscoveragecapability.Usingsatellitemobilecommunications,itispossibletoestablishaglobalsea,land,andairintegratedcommunicationsystemwithoutbeingrestrictedbygeographicalenvironment,climateconditionsandtime.

⑥Theabilitytoconstructwide-areacomplexnetworktopologies.Thehighpowerdensityandflexiblemulti-pointbeamcapabilityofsatellitecommunicationscombinedwithon-boardswitchingprocessingtechnologycanprovideawiderangeofpoint-to-pointandmulti-point-to-multipointcomplexnetworktopologiesatanexcellentprice-performanceratio.

⑦Safetyandreliability.Factshaveprovedthatinthefaceofearthquakerelieforinternationalsubmarine/opticalcablefailures,satellitecommunicationisanunparalleledimportantmeansofcommunication.Eveniftherearemoreperfectself-healingbackuporcircuitousterrestrialfiberopticcableandsubmarinefiberopticcablenetworksinthefuture,wisenetworkplannersanddesignerscanstillunderstandtheimportanceandimportanceofsatellitecommunicationsasthebasiclinkofthetransmissionmediumemergencybackupandinformationhighwayhybridnetwork.necessity.

Advantagesofsatellitecommunication

Themainadvantagesofsatellitecommunicationaresummarizedasfollows:

1.Longcommunicationdistance:Thelongestcommunicationdistanceinthesatellitebeamcoveragearea13000kilometers;

2,notrestrictedbyanycomplicatedgeographicalconditionsbetweenthetwopointsofcommunication;

3,notaffectedbyanynaturaldisastersandman-madeeventsbetweenthetwopointsofcommunication;

4.Thecommunicationqualityishighandthesystemreliabilityishigh.Itisoftenusedasasupportsystemduringthesubmarinecablerepairperiod;

5.Thelongerthecommunicationdistance,thelowertherelativecost;

6.ItcanrealizethetransmissionanddatainteractionofTVprograms,radioprogramsandnewsinalargearea;

7.Itishighlymobileandcanrealizesatellitemobilecommunicationandemergencycommunication;

8.Thesignalconfigurationisflexible,whichcanprovidehundreds,thousandsoreventensofthousandsofvoicechannelsandmediumandhigh-speeddatachannelsbetweentwopoints.

9,easytoachievemulti-addresstransmission;

Satellite Communications

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10.Itiseasytorealizeavarietyofbusinessfunctions.

Disadvantagesofsatellitecommunication

Talkingaboutsomanyadvantagesofsatellitecommunication,satellitecommunicationalsohasmanydisadvantages!

1.Longtransmissiondelay:500Timedelayofmillisecondto800milliseconds;

2,itisdifficulttorealizesatellitecommunicationinhighlatitudeareas;

3,inordertoavoidmutualinterferencebetweensatellitecommunicationsystems,satellitesinsynchronousorbitsThereisalimittothenumberofsatellites,andthenumberofsatellitescannotbeincreasedwithoutlimit;

4.Thesolartransitandeclipsephenomenainspacewillinterruptandaffectsatellitecommunications;

5,Thesuccessrateofsatellitelaunchis80%,andthelifetimeofthesatelliteisseveraltotenyears;thedevelopmentofsatellitecommunicationsrequireslong-termplanningandtheriskoflaunchfailure.

Thecharacteristicsofsynchronoussatellitecommunication

Themainadvantagesare:①Thecommunicationdistanceislong,andthecommunicationdistanceofonehopinthesatellitebeamcoverageareaisabout13×103km(usingtheglobalbeam,Theelevationangleoftheearthstationtothesatelliteisabove5°);②Itisnotrestrictedbyanycomplicatedgeographicalconditionsbetweenthetwopointsofcommunication;③Itisnotaffectedbyanynaturaldisastersandman-madeeventsbetweenthetwopointsofcommunication;④OnlyonehopthroughthesatelliteItcanreachtheotherparty,sothecommunicationqualityishigh,andthesystemreliabilityishigh.Itisoftenusedasthesupportsystemduringthesubmarinecablerepairperiod;⑤Thelongerthecommunicationdistance,thelowerthecost;⑥ItcanrealizeTVprograms,radioprogramsandnewsinalargearea.Itissuitableforbroadcastanduser-typeservices,aswellasinteractivedatatransmissionandevenvoicetransmissiondirectlytotheuser’sofficebuilding;⑦highflexibility,canrealizesatellitemobilecommunicationandemergencycommunication;⑧flexibility,canbebetweentwopointsProvidehundreds,thousandsoreventensofthousandsofvoicechannels,providetensofmegabits(Mbit/s)oreven120Mbit/smediumandhigh-speeddatachannels,andcanalsoprovideatleastonevoicechannelor1.2kbit/s,2-4kbit/sdatachannel;⑨easytorealizemulti-addresstransmission;⑩hasthefunctionoftransmittingmultipleservices.

Themaindisadvantagesare:①Thetransmissiondelayislarge.Thesatelliteearthstationcommunicatesthroughtheforwardingofacommunicationsatelliteabout36,000kmabovetheequator.Dependingonthelatitudeoftheearthstation,theone-wayspacedistanceofonehopis72,000～80,000km.Theradiowavepropagatingataspeedof300,000km/scanreachtheoppositeearthstationafteraspacetransmissiondelayof240msto260ms.Inaddition,thedelaywillincreaseduetotheprocessingtimeofthedigitalsignalbytheterminalequipment.AccordingtotherecommendationoftheInternationalTelegraphandTelephoneConsultativeCommittee(Rec.114),one-waytransmissionshouldnotexceed400ms.Foracall,ittakes500msto800msforthecallertoheartheotherparty'simmediatereply,whichisacceptableandaccustomedtothecaller.However,theleakagecausedbytheimbalanceofthetwo/four-wirehybridcoilsofthetwopartiesintheconversationwillcauseunbearableechoes.Therefore,echocancellersmustbeinstalledwithoutexception.②Atlatitude75south.Inhighlatitudesaboveandabove75°northlatitude,itisdifficulttorealizesatellitecommunicationbecausetheelevationangleofthesynchronoussatelliteislessthan5°.Generallyspeaking,thegroundatthelatitudebelow70°andtheaircraftbelow80°canbeestablishedviathesynchronoussatellite.Communication.③Thelocationofthesynchronousorbitislimited,andthenumberofsatellitesandthedistancebetweensatellitescannotbeincreasedindefinitely.④Everyyear,thereareunavoidableinterruptionsofsolartransitandstareclipsesthatmustbetakenthrough.⑤Itisnecessarytohavealong-termplanforsatellitedeployment.Theservicelifeofasatelliteisgenerallyseveraltotenyears,andthedesignandproductioncycleofasatelliteislong.Itisnecessarytoarrangeasuccessorsatelliteasearlyaspossible.However,thesatellitelaunchsuccessrateisabout80%onaverage,socertainrisksmustbeassumed.

Relatedcategories

Thedevelopmentofnewsatellitecommunicationtechnologiesisendless.Forexample,theverysmall-apertureantennaearthstation(VSAT)systemandthemobilesatellitecommunicationsysteminlow-mediumorbithavereceivedextensiveattentionandapplications.Satellitecommunicationisalsoanimportantpartofthefutureglobalinformationhighway.Itisknownforitswidecoverageandlargecommunicationcapacity.Theadvantagesoflong-distancecommunication,nogeographicalenvironmentrestriction,excellentquality,andhigheconomicbenefitswerefirstappliedinChinain1972anddevelopedrapidly.Togetherwithopticalfibercommunicationanddigitalmicrowavecommunication,ithasbecomethebackboneofcontemporarylong-distancecommunicationinChina.

Sincesatellitecommunicationisnotrestrictedbygeographicalconditionsandhasflexiblemobility,itstilldevelopsinnovativelybasedonitsadvantages.However,itisalsochallengedbytherapiddevelopmentofopticalfibercommunications.Ithasalargercapacityandhighertransmissionratethansatellitecommunications.Manytransoceaniccommunicationshavebeenreplacedbysubmarineopticalcables,andsimilarsituationsexistonlandtrunklines.Inthemidtolate1990s,satelliteTVlivebroadcasting(DBs-DirectBroadcastSatelliteorDTH-DirectToHome),satellitesoundbroadcasting,satellitemobilecommunications,andsatellitebroadbandmultimediacommunicationsbecamethefournewdevelopmenttrends.

FixedSatelliteCommunications

TheIntelsatseriesoftheInternationalSatelliteCommunicationsOrganizationhasbeendevelopedtotheninthgeneration.Thebusinessvolumehasbasicallygrownsteadilyfrom1996to2004.Thetotalglobalrevenuein2004was94BillionUSdollars,theUnitedStatesisexpectedtoreachonemillionusersin2006,andVSATapplicationswillincreaseby15%-20%annually.Broadbandaccessandmultimediaservicesaregraduallydeveloping.Ka-bandwillbecomethemainstreamofbroadbandservices.LeadingbroadbandservicesareCanada’stelecommunicationssatellites.Company(Telesat),WildBlueCompanyoftheUnitedStatesandShinSatelliteCompanyofThailand.

Intermsofsatelliteperformance,increasethetransmissionpower,increasetheEIRPvalue,increasethenumberofsatellitetransponders,increasebandwidth,reducecosts,andreducethesizeandcostofgroundterminalequipment.TheAniklaunchedbyCanadaonJuly18,2004.TheF2satellitehasatotalof114transponders,50ofwhichareintheKa-band.TheIpstarsatellitelaunchedonAugust11,2005inThailandhas114transpondersandacommunicationcapacityof45Gbit/s.Itiscurrentlytheworld’slargestcommercialcommunicationssatelliteinEurope.Largersatellitesarebeingdevelopedand250transpondersarebeinginstalled,whicharescheduledtobelaunchedin2008.

Thesatelliteusesdigitalsignalprocessorstoimprovesignalexchangecapabilities,reducegroundequipment,establishearthstationswithtelemetry,remotecontrol,trackingandmonitoringfunctions,andnetworkmanagementfunctionstorealizesatellitedynamiccontrolandmanagement.Satellitebroadbandcommunicationisusedtobroadcastlivehigh-definitionTV,andconnecttotheInternettodevelopnetworkTV.

Mobilesatellitecommunications

Mobilesatellitecommunicationscanbeglobalorregional,usingmediumandlow-orbitsatellitesglobally.Geostationaryorbitcommunicationsatellitesareusedregionally.RegionalmobilecommunicationsatellitesincludeIndonesia’sAsianCellularSatellite(Aees),alsoknownasGarula-1,launchedonFebruary12,2000.Itistheworld’sfirstregionalmobilecommunicationsatellite.Itisapersonalgeostationaryorbitpersonalmobilecommunicationsatellitewith140spotbeamsand11,000simultaneousvoicechannels.ThebeamcoverstheAsia-Pacificregion,whichaccountsfor60%oftheworld’spopulation.TheUnitedArabEmirateslaunchedThuraya_1and-2satellitesonOctober20,2000andJune10,2003,respectively.Eachsatellitehasacapacityof13,750simultaneouscalls.ItcoversEuropeandAsia.,Non-106countries.

InternationalMobileSatelliteCorporationlaunchedthefourth-generationInmarsat-4satelliteinMarch2005.Ithasaglobalbeam,19widespotbeamsand228narrowspotbeams,andtwosatellitessupporttheInmarsatsystem.Mostofthebusiness.ItwillintroduceaseriesofnewservicesoftheBroadbandGlobalAreaNetwork(BGAN)withatransmissionrateof432kbit/s.ThesatellitewilluseanL-bandantennaandadigitalsignalprocessor(DSP).TheDSPhaschannelselectionandbeamformingfunctionstogeneratebroadbandChannelmatchingpowerandbandwidthresources,DSPcanalsotailorthesatellitecoverageandadjustthebeamtomeettherequirementsofcapacityandbusinesstypes,andcanalsohandlethefailureofsolid-statepoweramplifiersandlownoiseamplifiers.ThebroadbandglobalareanetworkwilltransmitInternet,intranet,video-on-demand,videoconferencing,fax,e-mail,telephoneandlocalareanetworkaccessservices.

Thebusinessofglobalmobilesatellitecommunicationsinlowandmediumorbitsismainlyvoiceanddata.ItcanalsobeconnectedtotheInternettofurtherdevelopmultimediacommunications.

Thegeneraldevelopmenttrendofsatellitecommunicationislarge-capacity,high-power,high-speed,broadband,low-cost,high-transmittingfrequency,multi-transponder,multi-spotbeamandshapedbeam,whichareappliedonsatelliteProcessingtechnologyswitchingsignals,processingsignals,etc.,inthe21stcentury,directsatellitetelevision(DBS-TV),personalmobilesatellitecommunications,multimediasatellitecommunications,satelliteaudiobroadcasting,satellitenetworktelevision,etc.willbedevelopedinalargeamount.ThebusinessscopeofVSATcontinuestoexpandandpenetratesintovariousfieldsofthenationaleconomy,showingitseconomicandsocialbenefits.TheapplicationofKa-bandmakestheequipmentmorecompact,andofcourseitalsobringsseriousattenuationdefects.Theapplicationofopticalcommunicationinsatellitecommunicationhasgraduallybecomematureanddesirable.Itrequiresprecisesatellitecontroltechnology.Itisstillintheinternationalresearchanddevelopmentstageandisexpectedtoenterthepracticalstagesoon.

China’ssatellitecommunicationsindustryisalsodevelopingrapidly.OnApril12,2005,theAsia-Pacific-6(Apstar-6)satellitewaslaunched.Ithas38C-bandand14Ku-bandtransponders.In2006,itlaunchedthedirectbroadcastsatelliteSino-2(Sino-2),whichhas22Ku-bandtransponders(currentlythereisatechnicalfailure).Theapplicationfieldsofsatellitecommunicationarecontinuouslyexpanding.Inadditiontofinance,securities,postandtelecommunications,meteorology,earthquakeandotherdepartments,distanceeducation,telemedicine,emergencydisasterresponse,emergencycommunications,emergencytelevisionbroadcasting,sea,landandairnavigation,Internettelephones,televisions,etc.Willbewidelyused.China’ssatellitelaunchtechnology,theLongMarchseriesofcarrierrocketsleadtheworld,andChinahassuccessfullytestedlarge-thrust,non-polluting,non-toxicandenvironmentallyfriendlyrocketengines.ThishascreatedadvantagesforthedevelopmentofChina’slarge-scalecommunicationsatellitesandevenmannedspaceflightandlunarexplorationprojects.condition.

Chinawillmovealongthelong-termdevelopmentdirectionofintegrationofworldandearth,complementaryadvantages,andmilitary-civilianintegration.

Historicalreview

AsearlyasOctober1945,ArthurC.Clarkeproposedtheideaofgeostationarysatellitecommunication.Inthe10thissueoftheBritish"RadioWorld"magazine,hepublishedanarticleentitled"ExtraterrestrialRelay-CanSatellitesProvideRadioCoverageonaGlobalRange?"Communicationlaidthetheoreticalfoundation.ThedevelopmentofmodernsatellitecommunicationshasconfirmedthescientificnatureofClark'svision.

Thedevelopmentprocessofsatellitecommunicationscanbedividedintothefollowingtwostages.

(1)Theexperimentalphaseofsatellitecommunications

Since1954,theUnitedStateshassuccessivelyusedthemoon,passiveballoonsatellites,andcopperneedlepassivedipolebeltsasrelaystations.PassivesatellitecommunicationtestssuchastelephoneandTVtransmissionhaveprovedtobeoflittlepracticalvalue.Itwasnotuntil1957thattheformerSovietUnionlauncheditsfirstartificialsatellite,whichmadesatellitecommunicationsentertheactivesatellitetestphase.

InDecember1958,theUnitedStatesusedanAtlasrockettolauncha150-poundlow-orbitsatelliteintoanellipticalorbit(perigee200km,apogee1700km),andlauncheditonboardTheoutputpowerofthemachineis8W,andthefrequencyis150MHz.Thesatelliteusestapetorecord,andrelaystheinformation(telephone,telegram)sentbystationAtostationBwithadelay.InOctober1960,theUSDepartmentofDefenselaunchedthe"Messenger"satelliteintoanorbitwithanaltitudeof1,000kmandaninclinationof28.3°,usingafrequencyof2GHz,andconductedalow-orbitdelaycommunicationtestsimilartotheabove.

InJune1962,NASAusedaDeltarockettosendthe"ElectricStar"satelliteintoanellipticalorbitof1060-4500km;inDecemberofthesameyear,itlauncheda"relay"satelliteandenteredWithanellipticalorbitof1270～8300km,manytelephone,TV,andfaxdatatransmissiontestshavebeencarriedoutbetweentheUnitedStates,Europe,andSouthAmerica,andtechnicalissuessuchassatellitecommunicationfrequency,attitudecontrol,telemetrytracking,andcommunicationmethodshavebeenconducted.Experimented.

Since1963,synchronoussatellitecommunicationexperimentshavebeencarriedout.InJuly1963andAugust1964,NASAlaunchedthreeSYNCOMsatellites.Thefirstonefailedtoenterthepredeterminedorbit;thesecondoneenteredatiltedorbitwithaperiodof24h;thelastoneenteredacircularshape.ThegeostationarygeostationaryorbitofChinahasbecometheworld’sfirstexperimentalgeostationarycommunicationssatellite.Itwasusedtosuccessfullycarryouttelephone,TVandfaxtransmissiontests,andinthefallof1964,itwasusedtobroadcasttheliveeventsoftheOlympicGamesheldinTokyo,JapantotheUnitedStates.Atthispoint,theexperimentalphaseofsatellitecommunicationsisbasicallyover.

(2)Thepracticalstageofsatellitecommunication

Atthesametimeasthedevelopmentofsatellitecommunicationtechnology,theorganizationresponsibleforsatellitecommunicationbusinessandmanagementhasgraduallybeencompleted.OnAugust20,1964,Inordertoestablishasingleglobalcommercialsatellitenetwork,11WesterncountriesincludingtheUnitedStatesandJapanestablishedatemporaryglobalcommercialsatelliteorganizationinWashington,USA,andofficiallynamedittheInternationalTelecommunicationSatelliteOrganization(INTELSAT,InternationalTelecommunicationSatelliteOrganization)inNovember1965.).Theorganizationlaunchedthefirstgenerationof"INTELSAT-I"(IS-I,formerlyknownas"MorningBird")intothegeostationaryorbitinApril1965,andofficiallyassumedtheinternationalcommunicationbusiness.Thismarksthebeginningofanewstageofpracticalityanddevelopmentforsatellitecommunications.

Currentstatusandprospectsofsatellitecommunicationsinmycountry

(1)Fixedservices

In1972,mycountrybegantobuildthefirstsatellitecommunicationsearthstation,whichwassuccessfulin1984Thefirstexperimentalcommunicationssatellitewaslaunchedin1985.In1985,fivepublicnetworkearthstationsincludingBeijing,Lhasa,Urumqi,Hohhot,andGuangzhouwerebuilttoformallytransmitCCTVprograms.Sincethen,internationalexportstationsinBeijing,Shanghai,andGuangzhouhavebeenbuilt,andabout25,000directinternationalsatellitelineshavebeenopened;Beijingisthecenter,andLhasa,Urumqi,Hohhot,Guangzhou,Xi’an,Chengdu,Qingdao,etc.aretheregionalcenters.Therearemorethan10,000domesticlinesinChina’smultipleearthstations.

Thedevelopmentofprivatenetworkconstructionisveryrapid,thePeople’sBankofChina,XinhuaNewsAgency,transportation,oilandgas,economyandtrade,railways,electricpower,waterconservancy,civilaviation,ChinaNationalNuclearCorporation,NationalEarthquakeAdministration,MeteorologicalAdministration,YunnanTobacco,ShenzhenStockcompanies,nationaldefense,publicsecurityandotherdepartmentshaveestablishedmorethan20satellitecommunicationnetworks,andsatellitecommunicationearthstations(especiallyVSAT)havereached10,000.

(2)SatelliteTVbroadcastingbusiness

In1984,the"Dongfanghong"satellitewassuccessfullylaunched,creatinganewerainmycountry'suseofsatellitestotransmitradioandtelevisionprograms.Asof2015,4setsofCCTV,EducationChannel,Xinjiang,Tibet,Yunnan,Guizhou,Sichuan,Zhejiang,Shandong,Hunan,Henan,Guangdong,Guangxi,Hebeiandothermorethanadozenprovincial-levelTVprogramsandmorethan40languagesBroadcastprogramshavebeentransmittedonsatellites.Thereare100,000satelliteTVterrestrialstationsandapproximately300,000TVstations(TVRO).Manysystemsusemoreadvanceddigitalcompressiontechnology.

(3)Satellitemobilecommunicationservices

Satellitemobilecommunicationmainlysolvesthecommunicationtasksbetweenvarioustargetsonland,seaandairandwithgroundpublicnetworks.AsamemberofINMARSAT,ChinahasashorestationinBeijing,whichcanprovidecommunicationservicesforthePacific,IndianOceanandAsia-Pacificregions.Inaddition,mycountryisgraduallydevelopingairbornesatellitemobilecommunicationsservices.石油、地质、新闻、水利、外交、海关、体育、抢险救灾、银行、安全、军事和国防等部门均配备了相应业务终端。现我国已进入INMARSAT的M站和C站，有近5000部机载、船载和陆地终端。

（4）未来展望

随着我国现代化建设和以多媒体为代表的信息高速公路的发展，今后10年我国卫星通信将有一个更大的发展，并将以我国自主的大容量通信卫星为主体，建立起完善、长期稳定运行的卫星通信系统。若以每年递增15%～17%计算，到2002年，卫星通信公用网开通的线路将是1996年的2.7～3倍，大、中城市将建立起大、中型卫星通信地球站约50～60座，中、小型地球站约200～300座(不包括VSAT站)。到2005年，卫星通信公用网线路将发展到数十万条。

我国今后卫星通信技术发展趋势为：

①开发新频段，提高现有频段的频谱利用率。从现有单一的C频段发展到Ku、Ka、UHF、L、S、X等频段。

②公用干线通信网向高速、数字、宽带发展，速率将达60Mbit/s、120Mbit/s和1000Mbit/s，并利用SDH和ATM，建立国家信息高速公路——天基宽带综合业务数字通信网。

③进一步发展小型化、智能化VSAT专用卫星通信网。业务也将从单一的数据或话音为主，发展为话音、数据、图文、电视兼容的综合业务。

④卫星移动通信系统将大力发展新技术，如星上大天线技术、多波束技术、星上交换、星上处理和星间链路技术、越区切换技术等。

⑤开展卫星通信网与其他异构网的互通、互联,完成异构网协议变换，网络同步与交换技术及信令呼叫接口技术等。

⑥网络管理和控制及网络动态分配处理的自动化技术。

⑦卫星通信网的网络安全、保密技术。

⑧与我国卫星通信设备产业化发展有关的生产、工艺加工技术等等。

展望21世纪，卫星通信将获得重大发展，尤其是世界上新技术，如光开关、光信息处理、智能化星上网控、超导、新的发射工具和新的轨道技术的实现，将使卫星通信产生革命性的变化，卫星通信将对我国的国民经济发展，对产业信息化产生巨大的促进作用。