Introduction
Withthecontinuousdevelopmentofinternationalcommunicationsatellites,especiallysincetheofficialprovisionofcommercialservicesbyInternationalMobileSatellitein1982,mobilesatellitecommunicationshavearousedgreatinterestandgreatinterestfromallcountriesintheworld.Attention,andtheemergenceofglobalpersonalcommunicationservices.Whatisthedifferencebetweenamobilecommunicationsatelliteandageneralcommunicationsatellite?
Classification
Oneisthesameasageneralcommunicationsatelliteinageostationaryorbit.ItstypicalrepresentativeisInternationalMobileSatelliteNo.3,whichwasusedforcommunicationin1998whenmycountrywasfightingfloods.However,duetothelongcommunicationdistance,weaksignal,andlargegroundequipment,itcangenerallyonlybeusedforcommunicationswithlargemobileuserssuchasships,airplanes,andvehicles.Eventheadvancedportableterrestrialterminalmustfindtheinternationalmobilesatellitebeforemakingacall,andcannotmoveduringthecall.However,ageostationaryorbitmobilecommunicationsatellitethatcanprovideservicesforpersonalmobilephoneshasbeendeveloped,andthe"AsianCellularSystem"(ACeS)launchedin2000isthefirst.
Theotheristhelow-orbitmobilecommunicationsatellitesystem.Itwasonlyproposedinthelate1980sandhasnowbecomeahotspotinthedevelopmentofmobilecommunicationsatellites.Thisisbecauseitsorbitislow,generallyataheightofabout500to1500kilometers.Duetotheshortsignaltransmissionrouteofthiskindoflow-orbitsatellite,thesignalattenuationlossisverysmall,thesignaltimedelayisalsoveryshort,almostimperceptible,canobtainthemosteffectivefrequencyreuse,andcanachievetrueglobalcoverage.Thiskindofmobilecommunicationsatelliteisnotlargeinqualityandvolume,soitsdevelopmentandproductioncycleisshort,andthedevelopmentcostislowerthanthatoflargesatellites.Likethefamous"Yixing"and"GlobalStar"belongtothissystem.Whenlaunchinglow-orbitsmallsatellites,severalsatellitescanbelaunchedatatime.
Thereisalsoamedium-orbitmobilecommunicationsatellitesystem.Itsorbitalheightisbetweenloworbitandgeostationaryorbit.TheICOsatelliteisatypicalone,withanorbitalheightof10,000kilometers.
Mobilecommunicationsatellitesgenerallyrequireonly3satellitestoachieveglobalcoverage,butthenorthandsouthpolesareblindareasthatcannotbecovered.Only12constellationsofmobilecommunicationsatellitesinmediumorbitareneeded.Alow-orbitmobilecommunicationsatelliteconstellationrequiresdozensorevenhundreds.Forexample,the"Yixing"constellationiscomposedof66satellites.
Geostationarysatellitemobilecommunicationsystem
Satellitecommunicationisradiocommunicationbetweenearthstationsorbetweenspacecraftandearthstationsusingsatellitetransponders,mainlyincludingsatellitefixedcommunication,satelliteTherearefourmajorareasofmobilecommunications,satellitedirectbroadcastingandsatelliterelaycommunications.Thefirstthreearecarriedoutbetweenearthstationsusingsatellitetransponders,andthelatterarecarriedoutbetweenspacecraftandearthstationsusingsatellitetransponders.Satellitemobilecommunicationisanindispensablemeanstorealizeglobalmobilecommunicationbecauseofitswidecoverage,siteconstructioncostandcommunicationcostindependentofdistance,anditisespeciallysuitableformobilecommunicationneedsinareaswhereitisdifficulttolaywiredcommunicationfacilities.
Inthelate1980sand1990s,duetotherapidriseofopticalfibercommunicationsystemsandgroundcellularmobilecommunications,satellitecommunicationslosttraditionalinternationalanddomesticlong-distancecommunicationsandlandmobilecommunicationsandothermajorterritories.However,sincethebeginningofthenewcentury,satellitecommunicationpositioninghasbecomemorereasonable,exploitingstrengthsandcircumventingweaknesses,andhasmadeconsiderableprogressinthecompetitionwithothercommunicationmethods.
Inthegeostationaryorbitsatellitemobilecommunicationsystem,the"InternationalMobileSatellite"(Inmarsat)systemthatprovidesglobalcoverage,theAsianCellularSatellite(ACeS)systemandtheThurayasystemthatprovideregionalcoverage,MSAT(renamedSkyTerra)systemandTerraStarsystem,etc.ThebeamcoverageoftheabovesystemsincludesInmarsat,ThurayaandACeSsystemsinChina.
InmarsatsystemisaglobalsatellitemobilecommunicationsystemoperatedbyInternationalMobileSatelliteCorporation.Sinceitsoperationin1982,thesystem'ssatelliteshavebeendevelopedtothefourthgeneration,anditsfifth-generationsatellitesarealsounderdevelopment.NowInternationalMobileSatelliteCorporationhasdevelopedintotheonlycompanyintheworldthatcanprovideglobal,all-weather,all-roundpubliccommunicationanddistressandsafetycommunicationservicesforusersinvariousindustriessuchassea,land,andair.Atpresent,Inmarsatuses3constellationscomposedof11GEOsatellitestoprovidesatellitemobilecommunicationservicesaroundtheworld,thelatestofwhichisits3Inmarsat-4satellites.TheInmarsat-4satelliteusesa9mdiameterL-bandlargeantennacapableofgeneratingmultiplebeamsandatransparentbent-tubedigitalsignalprocessor(DSP)withchannelselectionandbeamformingfunctions,withatotalof200spotbeams,With19widebeamsand1globalbeam,itsspotbeamsprovidetheuserterminalwithasatelliteequivalentomnidirectionalradiatedpowerofupto67dBW.
AsiaCellularSatellite(ACeS)systemisaregionalpersonalsatellitemobilecommunicationsystemestablishedbyIndonesiaandothercountries,coveringEastAsia,SoutheastAsiaandSouthAsiaItcoversanareaofmorethan2.848×107km2,andthetotalpopulationofthecountryinthecoverageareaisabout3billion.TheACeSsystemcanprovidedual-mode(satellite-GSM900)voice,fax,low-speeddata,Internetservices,andregionalroamingservicestovarioususerterminalsontheground,suchasfixed,mobile,portableandhandheld.TheACeSsystemusesaGarudasatellitetocompletecoverage.TheGarudasatelliteweighs4500kg,hasapowerof14kW,andhasadesignlifeof12years.TheserviceareacoverstheentireAsia.TheGarudasatelliteisequippedwithtwo12-meter-diameterL-bandtransmittingandreceivinglargeantennas,withatotalof140spotbeams,coveringabout45spotbeamsinmycountry,anditsequivalentomnidirectionalradiationpowerintensityisashighas73dBW.Thesatellitecanprovide11000telephonechannelsatthesametime,withatotalusercapacityofupto2million,andcanrouteandexchangevoicechannelsonthesatellite.InSeptember2006,ACeSandInmarsatreachedacooperationtoprovideglobalsatellitemobilecommunicationsservicesthroughACeS'sGaruda1satelliteandInmarsat'sInmarsat-4seriessatellites.
ThurayaSystemisaregionalgeostationarysatellitemobilecommunicationsystemestablishedbyThurayaSatelliteCommunicationsCompany,headquarteredinAbuDhabi,UAE.ThesatellitenetworkoftheThurayasystemcovers110countriesandregionsincludingEurope,NorthAfrica,CentralAfrica,mostofSouthAfrica,theMiddleEast,CentralAsia,andSouthAsia,coveringabout1/3oftheworld,andcanprovidesatellitemobilecommunicationservicesfor2.3billionpeople..TheThurayasystemterminalintegratesthethreefunctionsofsatellite,GSM,andGPS,andprovidesuserswithvoice,SMS,data(Internet),fax,andGPSpositioningservices.ThelaunchweightoftheThurayasatelliteis5250kg,andtheweightinorbitis3200kg.Thesolarbatteryprovides11~13kWofpower.Thesatelliteisequippedwitha12.25maperturesatelliteantenna,whichcangenerate250~300beamsandprovideGSMcompatiblemobilephoneservices..Mobilesatelliteterminalsincludehandheld,vehicle-mountedandfixedterminals.Thurayacanprovideatotalof13,750channelswithachannelbandwidthof27.7kHz,amodulationmethodofπ/4-QPSK,amultipleaccessmethodofFDMA/TDMA,andachannelbitrateof46.8kbit/s,whichcanprovideterminalswith2.4/4.8/9.6kbit/sdatatransmissionrate.
TerreStarThecompanysuccessfullylaunchedthelarge-capacitydedicatedgeostationaryorbitmobilecommunicationsatelliteTerraStar-1inJuly2009,whichcanbedevelopedinconjunctionwithavarietyofnewtechnologysystemssuchasWCDMA,CDMA2000orLTEterminal.TerraStar-1providesanext-generationall-IPsatellitenetworkcoveringtheUnitedStates,PuertoRicoandtheUSVirginIslands,andcanprovidevoiceanddataservices.TheTerraStar-1userlinkantennahasadiameterof18mandusesa2GHzS-bandfrequency.Thesatelliteweighs6900kgandsupportscommunicationwiththesame-sizedhandsetsinthegroundcellularnetwork.
SkyTerra,formerlyknownasMSV(MobileSatelliteVentures),inJuly2010,SkyTerrawasrenamedLightSquared.
MSVoriginallyusedtwoGEOsatellites,MSAT-1andMSAT-2,toprovidesatellitemobilephoneservices.InNovember2010,theSkyTerra1satellitecommissionedbyBoeingwassuccessfullylaunched.ThesatelliteusesBoeing's702HPplatform,weighs5360kg,andhasadesignlifeof15years.
Medium-orbitsatellitemobilecommunicationsystem
Themostwell-knownmedium-orbitsatellitemobilesystemsaretheOdysseysystemandtheICOsystem.Inaddition,ESAalsodesignedaMAGSS-14system.However,duetosomecommercialreasons,theyhavebeencancelledorhavenotbeensuccessfullyoperatedsofar.ThenewO3bmedium-orbitsatellitecommunicationsystemattemptstoprovidevoicecommunicationservicesonthebasisofsatellitebroadbandaccess.
TheOdysseysystemisamediumorbitsatellitemobilecommunicationsystemlaunchedbyTRW[10].TheOdysseysystemcanbeusedasasupplementandextensiontotheexistingland-basedcellularmobilecommunicationsystem,supportingdynamic,reliable,automatic,anduser-transparentservices.Themainuserterminalofthesystemisthehandset.Thesystemcanprovidevariousservices,includingvoice,fax,data,paging,messaging,positioning,etc.Thedatarateofthehandsetcanreach2.4kbit/s,anditcanalsoprovideadatarateof4.8to19.2kbit/s.DuetocommercialreasonswiththeICOsystem,theOdysseysystemwascancelledinDecember1997,andTRWbecamethemajorshareholderoftheICO.
ICO(IntermediateCircularOrbit)GlobalSatelliteCommunicationSystemisoperatedbyICOGlobalCommunicationsCo.,Ltd.TheICOsystemconsistsofaspacesegmentandagroundsegmentgroup.Thespacesegmentis12starslocatedinamid-circleorbit,andthegroundsegmentiscalledICONET.TheICOsystemisconnectedwiththeexistingterrestrialfixedandmobilecommunicationnetworkstoformacompleteworld-earthcombinationsystem,usingmulti-modemobilephonesorotherterminalstorealizecommunicationanytimeandanywhere.ThespacesegmentoftheICOsystemconsistsof12satellitesatmediumorbitalaltitude(MEO),ofwhich10arethemainsatellitesandtheother2arethestandbysatellitesinorbit.Thesystemadoptsaninclinedcircularorbitwithanorbitalheightof10390kmandanorbitalinclinationangleof45°.Allsatellitesaredistributedontwomutuallyperpendicularorbitalplanes,andeachorbitalplanehasabackupsatellite.ThelaunchweightoftheICOsatelliteis2600kgandthedesignlifeisabout12years.Thesatelliteusesgalliumarsenidesolarcells,whichcanprovidemorethan8700Wofpowerattheendofthesatellite'slife.Eachsatellitecanprovide4,500channels.TheICOsatelliteusesanindependentuserlinktransceiverantenna.TwoantennasareinstalledontheICOsatellitestarwithadiameterofmorethan2mandadoptsdigitalbeamformingtechnology.Eachuserlinkantennaiscomposedof127radiatingelements,whichareusedtogenerate163receivingortransmittingspotbeams.EachICOspotbeamwillprovidetheuserlinkwithaminimum8dBlinkmarginexceeding10dBonaverage.
MAGSS-14(MediumAltitudeGlobalSatelliteSystem)isamediumorbitsatellitemobilecommunicationsystemdesignedtosupportvoicecommunicationbetweenhandsetsandmobileterminals,developedbyESA.ThespacesegmentoftheMAGSS-14systemincludesaconstellationcomposedof14medium-orbitsatellites.Thisdesignisveryconducivetothesteppedupgradeofthesystemandcancompleteglobalcoverage.ThesystemrealizescommunicationwithuserterminalsontheLfrequencyband.Thesystemhasnotyetbeensuccessfullydeployed.
O3bisanewmedium-orbitsatellitecommunicationsystemthatprovidesbroadbandnetworkaccessthroughsatellites,whichcanprovidevoicecommunicationanddatatransmissionservices,andisdevelopedbyO3bNetworks.O3bNetworksisanInternetaccessservicecompanyjointlyestablishedin2007byorganizationssuchasInternetgiantGoogle,mediagiantJohnMalone'soverseascableoperatorLibertyGlobal,andHSBC.O3bprovidessatellitecommunicationservicesinmorethan150countriesinAsia,Africa,LatinAmericaandtheMiddleEast,andprovidesafiber-opticsatellitebackbonenetworkfortelecomoperatorsandISPs.O3bwillbetheworld'sfirstsatellitenetworkusingMEOsatelliteswithultra-lowlatency,Ka-band,andopticalfiberspeed.TheO3bsatellitetransponderhas3to4timesthecapacityoftheGEOsatellitesystem,whichallowsuserstoenjoynetworkbandwidthsimilartoopticalfiberaccess.DuetotheuseofMEOsatellites,thenetworkround-tripdelayisonlyabout100ms.TheO3bsatelliteconstellationisplannedtobedeployedin2012.Eightsatelliteswillbelaunchedtoformthefirstphaseoftheconstellation,andwillbeexpandedto16satellitesinthefuture.
Low-orbitsatellitemobilecommunicationsystem
Sincethe1990s,low-orbitsatellitemobilecommunicationsystemshaveattractedwideattention.Countriesaroundtheworldhavedevelopedmanylow-orbitsatellitemobilecommunicationsystems.ThebankruptcyoftheIridiumsystemin2000causedthisboomtocooldownrapidly.Severaltypicallow-orbitsatellitemobilecommunicationsystemsincludeIridium,Globalstar,Orbcomm,Teledesic,etc.Atpresent,onlyIridium,Globalstar,andOrbcommhavebeensuccessfullyoperated.
IridiumSystemisalow-orbitsatelliteglobalmobilecommunicationsystemcomposedof66low-orbitsatellites.ItbegancommercialoperationinNovember1998andwentbankruptinMarch2000.TheIridiumSatelliteCompanywasestablishedandre-providedcommunicationservices.Theglobalcoverageofthesystemincludesthetwopoles.Theon-boardtransponderusesadvancedprocessingandswitchingtechnology,multi-spotbeamantennas,andhasinterplanetarylinks.Itisthemostadvancedlow-orbitsatellitecommunicationsystem;itsinterplanetarylinksandfeederlinksareKafrequencyband,theuserlinkisLfrequencyband,whichprovidesservicessuchastelephone,fax,data,andpaging.Userterminalsincludesingle-mode,dual-modeandtriple-modemobilephones,vehicle-mounteddevicesandfixedterminals.AftertheestablishmentofthenewIridiumCorporation,itiscurrentlyoperatingwellduetogovernmentsupportandlargeordersfromtheU.S.military.Atpresent,IridiumSatelliteCompanyisactivelydevelopingitsnew"NEXT"satelliteconstellationplan.NEXTisaboldideaforthesecond-generationsatelliteconstellation.NEXTusestheexistingIridiumconstellationstructuretocomplete100%coverageoftheentireearth.Design81satellites(66toreplacetheexistingconstellation,6inorbitbackup,9groundbackup).NEXTwillgreatlyenhancetheexistingIridiummobilecommunicationservices(higherdatarate,strongerservicesandequipment,cantakeadvantageoftheadvantagesofIPtechnology,andbackwardcompatiblewithexistingequipment).NEXTcanalsoprovidebusinesses,governments,scientificresearchinstitutions,etc.withtheserviceofplacingsensorloadsonsatellites,whichcanrealize7×24-hourreal-timemonitoringoftheearth'ssurfaceandatmosphere.NEXTisexpectedtobedeployedin2017.
GlobalStarSystemisaglobalsatellitemobilecommunicationsystemcomposedof48low-orbitsatellites.Commercialoperationbeganin1999.Thesatelliteusesatransparenttransponderandamulti-beamantenna.TheuserlinkandthefeederlinkarebothintheVHFfrequencyband,providinguserswithservicessuchaspaging,fax,shortdata,andpositioning.Userterminalsincludemobileterminalssuchasmobilephones,vehicle-mounted,airborne,andshipborne,aswellassemi-fixedandfixedterminals.Afterenteringthe21stcentury,Globalstar'sbusinessdevelopmentisnotreasonable
Ithink,butin2009,GlobalstarsuccessfullyobtainedfinancingfromtheFrenchexportcreditagencyCoface,whichwillprovidesufficientfinancialmotivationforitsfuturebusinessdevelopment.
Orbitalcommunicationsystem(Orbcomm)isaLEOsatellitemobilecommunicationsystemjointlyoperatedbyOrbcommoftheUnitedStatesandTeleglobeofCanada.Thesystemisaglobalsatellitemobilecommunicationsystemcomposedof29low-orbitsatellitesThecommunicationnetworkprovidesuserswithsatellitemobilecommunicationservices.Commercialoperationsbeganin1997.Thesatelliteusesaprocessingtransponderandasingle-beamantenna,andtheterminalisasingle-modemobilephoneandapager.Currently,Orbcommusesitslow-orbitsatellitestoprovidelow-speed,low-cost,nearreal-timetwo-waydatatransmissionservices.ItsuniqueM2M(MachinetoMachine)-centricnetworkrealizeslow-speedconnectionofuserequipmentatalowercost,including"satelliteM2M","terrestrialM2M"and"dual-modeM2M",whichcanutilizesatelliteandterrestrialcellularnetworksRealizeassettracking,managementandremotecontrol.InSeptember2009,OrbcommandSpaceExplorationTechnologies(SpaceX)jointlyannouncedthattheywouldlaunch18second-generationsatellites,withtheplannedlaunchtimebetween2010and2014.
TheTeledesicsystemisalow-orbitsatellitecommunicationsystemdevelopedbyTeledesic(foundedinJune1990).ItprovidesInternetaccessservicesforterrestrialsatelliteterminalsthroughlow-orbitsatellites.Atthesametime,voicemobilecommunicationcanberealizedonthebasisofnetworkaccess.TheTeledesicsystemwasinvestedandconstructedbyCraigMcCawandBillGates,andfirstobtainedtheallocationoftheKafrequencybandfornon-GEOsatelliteservices.TheinitialgoaloftheTeledesicsystemistousemorethan900low-orbitsatellitestoprovideInternetaccessservicesclosetofiber-opticquality,andtoachieveseamlessintegrationwithterrestrialfiber-opticnetworks.DuetotheimpactofthefailureoftheIridiumsatellitesystem,theTeledesicsystemhasreducedthescaleandcomplexityofitsoriginalplan,andthesystemhasnotyetbeensuccessfullydeployed.
Performance
Thesizeandtransmitpowerofthetransmittingandreceivingantennasofmobilecommunicationsatellitesaregenerallyrelativelyhigh,andtheL-bandtransmissionsignalwithlowrain-inducedattenuationandlowsignaltransmissionlossisusedtoreduceThesizeofthegrounduserterminalissmall,easytocarry,andthecommunicationqualityisguaranteed.
Mobilecommunicationsatellitescannotonlyprovidecommunicationservicesforlargemobileusers,suchasships,airplanesandvehicles,butalsoenablepersonalmobilephonestodirectlycommunicatewithsatellites."Star"istypical.Undercertaincircumstances,theyreflectthesuperioritythatothercommunicationsystemsdonothave.Forexample,expeditionersgoingtothepolarregionscaneasilycommunicatewithChinausingthe"Yixing"mobilephone,whichdwarfsothercommunicationmethods.IntheeventofanearthquakeinIndiaandTaiwan,othercommunicationmethodsaredamaged."Themobilephonecanstillworkreliablytoensurecommunicationwiththeoutsideworld.
Advantages
So,cantheuserdirectlywatchorlistentotheprogramtransmittedbythesatellite?Mobilecommunicationsatellitescandirectlyprovidevoicecommunicationservicesforusers,butcannotforwardTVprograms.RetransmissionofTVprogramsisdonebyliveTVsatellites.Userscandirectlywatchorlistentotheprogramstransmittedbythesatellite,butgenerallytheycanonlywatchandlistentotheprogramsatafixedlocation.DirectTVsatelliteshavebecomeahotspotincontemporarydevelopment.Thecharacteristicsofthiskindofsatellitesareroughlysimilartothoseofmobilecommunicationsatellites,namelyhigh-powertransmissionofdownlinksignals,large-areasolararrays(guaranteedtoprovidepowerabovekilowatts),high-precisionorbitcontrolandantennapointing,etc.Theseareallforreducingtheburdenonthegroundusersandminiaturizingtheirreceivingterminals.Inotherwords,itistoleavethedifficultytothesatelliteandtheconveniencetotheuser.
ContemporaryTVlivesatellitesusedigitalvideocompressiontechnology,whichgreatlysavesbandwidthandincreasestherateofvideodatatransmission.ThiskindofsatelliteusingdigitalvideocompressiontechnologycanprovidehundredsofTVprograms.Thefamilyonlyneedstoinstalla0.45mdiameterantennaandreceiverdecodertowatchhigh-qualitysatelliteTVprogramsdirectlyontheTV.