TechnicalEnglishForInformationScienceandElectronicEngineeringUnit7SatelliteCommunicationsPartIApplicationsofCommunicationssatellite3NewWordsabbreviate縮略，簡寫成geostationaryorbit對地靜止軌道ellipticalorbit橢圓軌道complementary互補的，補充的submarine海底的，潛水艇relay中繼，接力analogous模擬的，類似的disturbance擾動，干擾constellation星座圖，星羅棋布geosynchronous地球同步的affiliate會員，分支機構limelight眾人注目的中心diameter直徑free-to-airTV不加密不收費電視headend數(shù)據(jù)轉發(fā)器ambiguous模糊的，混淆的transponder轉發(fā)器，應答器space-bornerepeater天空轉發(fā)器amateur業(yè)余愛好，業(yè)余的dialup撥號41Acommunicationssatellite(sometimesabbreviatedtocomsat)isanartificialsatellitestationedinspaceforthepurposesofmunications.Moderncommunicationssatellitesuseavarietyoforbitsincludinggeostationaryorbits,ellipticalorbitsandlow(polarandnon-polar)Earthorbits.停留在太空現(xiàn)代通信衛(wèi)星使用多種軌道，包括對地靜止軌道、橢圓形軌道、低地球軌道（過極地和不過極地）。52Forfixed(point-to-point)services,communicationssatellitesprovideatechnologycomplementarytothatoffiberopticsubmarinecommunicationcables.Theyarealsousedformobileapplicationssuchascommunicationstoships,vehicles,planesandhand-heldterminals,andforTVandradiobroadcasting,forwhichapplicationofothertechnologies,suchascable,isimpracticalorimpossible.1它們也可用于如船，車輛，飛機和手持終端的移動通信，用于電視和無線電廣播，以及應用其它技術，比如電纜，是不現(xiàn)實或不可能的地方。63TelephonyThefirstandhistoricallythemostimportantapplicationforcommunicationsatellitesisininternationaltelephony.Fixed-pointtelephonesrelaycallstoanearthstation,wheretheyarethentransmittedtoageostationarysatellite.

固定電話將通話傳輸?shù)降孛嬲?，在那里再發(fā)射到對地靜止衛(wèi)星上73Ananalogouspathisthenfollowedonthedownlink.Incontrast,mobiletelephones(toandfromshipsandairplanes)mustbedirectlyconnectedtoequipmenttouplinkthesignaltothesatellite,aswellasbeingabletoensuresatellitepointinginthepresenceofdisturbances,suchaswavesonboardaship.2相反，移動電話（船和飛機上接收和發(fā)送的）必須直接連到設備把信號上傳到衛(wèi)星，又能確保在有干擾時的衛(wèi)星指向，如船上的電波干擾。84Improvementsinsubmarinecommunicationscablescausedadeclineintheuseofsatellitesforfixedtelephonyinthelate20thcentury.Handheldtelephones(cellularphones)usedinurbanareasdonotmakeuseofsatellitecommunications.Insteadtheyhaveaccesstoagroundbasedconstellationofreceivingandretransmittingstations.海底通信電纜的改進導致了20世紀后期用于固定電話的衛(wèi)星應用有所下降。接入地面上用于接收和發(fā)射的星羅棋布的基站群95SatelliteTelevisionandradioTelevisionbecamethemainmarket,itsdemandforsimultaneousdeliveryofrelativelyfewsignalsoflargebandwidthtomanyreceiversbeingamoreprecisematchforthecapabilitiesofgeosynchronouscomsats.3TwosatellitetypesareusedforNorthAmericantelevisionandradio:DirectBroadcastSatellite(DBS),andFixedServiceSatellite(FSS).電視成為主要市場，其對相對很少的大帶寬信號同時傳送給很多接收機的要求更好地匹配了對地靜止通信衛(wèi)星的性能。106AdirectbroadcastsatelliteisacommunicationssatellitethattransmitstosmallDBSsatellitedishes(usually18to24

inchesindiameter).DirectbroadcastsatellitesgenerallyoperateintheupperportionofthemicrowaveKuband.DBStechnologyisusedforDTH-oriented(Direct-To-Home)satelliteTVservices.直播衛(wèi)星是一種通信衛(wèi)星，它直接向小型DBS衛(wèi)星天線發(fā)射。117FixedServiceSatellites(FSS)usetheCband,andthelowerportionsoftheKubands.Theyarenormallyusedforbroadcastfeedstoandfromtelevisionnetworksandlocalaffiliatestations,aswellasbeingusedfordistancelearningbyschoolsanduniversities,businesstelevision,videoconferencing,andgeneralcommercialmunications.4FSSsatellitesarealsousedtodistributenationalcablechannelstothecentralcontrolunits.它們通常用于向電視網和加盟地方臺饋送或收集廣播節(jié)目，也用于中小學和大學的遠程教學、商業(yè)電視、視頻會議和一般商用通信。

128FSSsatellitesdifferfromDBSsatellitesinthattheyhavealowerRFpoweroutputthanthelatter,requiringamuchlargerdishforreception(3to8

feetindiameterforKuband,and12

feetonupforCband),aswellasusinglinearpolarizationforeachofthetransponders’RFinputandoutput(asopposedtocircularpolarizationusedbyDBSsatellites).5FSS與DBS的不同之處在于固定業(yè)務衛(wèi)星具有更低的射頻功率輸出，需要更大的碟形衛(wèi)星接收天線，收發(fā)器的射頻輸入和輸出也都采用線極化。138FSSsatellitetechnologywasalsooriginallyusedforDTHsatelliteTVfromthelate1970stotheearly1990sintheUnitedStatesintheformofTVRO(TeleVisionReceiveOnly)receiversanddishes.149ThisallchangedwhenthefirstAmericanDBSprovider,DirecTV,wasestablishedin1994,stealingthelimelightfromFSSsatellitetechnologyforDTHprogramming.However,FSSsatellitesontheCandKubandsarestillusedbycableandsatellitechannelssuchasCNN,TheWeatherChannel,HBOandothers,fordistributiontocableTVheadends,andtotheDBSprovidersthemselveswhothenre-distributethesechannelsovertheirownDBSsystems.奪去了FSS衛(wèi)星技術在DTH節(jié)目方面的風頭1510Free-to-airsatelliteTVchannelsarealsousuallydistributedonFSSsatellitesintheKuband.TheIntelsatAmericas5,Galaxy10RandAMC3satellitesoverNorthAmerica

provideaquitelargeamountofFTAchannels

ontheirKubandtransponders.在他們的Ku波段收發(fā)器上提供相當多的FTA頻道。1611TheAmericanDishNetworkDBSservicehasalsousedFSStechnologyduetotheirneedformorecapacitytocarrylocaltelevisionstations,andformorebandwidthtocarryHDTVchannels.SatellitesforcommunicationhavenowbeenlaunchedthathavetranspondersintheKaband.NASAaswellhaslaunchedexperimentalsatellitesusingtheKabandrecently.由于傳輸?shù)胤诫娨暸_節(jié)目需要更大的容量1712ThedefinitionsofFSSandDBSsatellitesoutsideofNorthAmerica,especiallyinEurope,areabitmoreambiguous.Mostsatellitesusedfordirect-to-hometelevisioninEuropehavethesamehighpoweroutputasDBS-classsatellitesinNorthAmerica,butusethesamelinearpolarizationasFSSsatellites.Becauseofthis,thetermsFSSandDBSaremoresousedthroughouttheNorthAmericancontinent,andaremoninEurope.歐洲大部分用于直播的衛(wèi)星使用與北美DBS級同樣級別的功率輸出，卻使用與FSS衛(wèi)星一樣的線性極化。1813AmateurradioAmateurradiooperatorshaveaccesstotheOSCARsatellitesthathavebeendesignedspecificallytocarryamateurradiotraffic.Mostsuchsatellitesoperateasspace-bornerepeaters,andaregenerallyaccessedbyamateursequippedwithUHForVHFradioequipmentandhighlydirectionalantennassuchasYagiordishantennas.被設計成承載業(yè)余無線電通信流量通常被裝備UHF或VHF設備并使用高度方向性天線如八木天線或拋物面天線的業(yè)余無線電接入1913Duetothelimitationsofground-basedamateurequipment,mostamateursatellitesarelaunchedintofairlylowEarthorbits,andaredesignedtodealwithonlyalimitednumberofbriefcontactsatanygiventime.Somesatellitesalsoprovidedata-forwardingservicesusingtheAX.25orsimilarprotocols.大多數(shù)業(yè)余衛(wèi)星發(fā)射到低地軌道上，并設計得只能在任何給定時刻進行有限次數(shù)的簡短接觸。數(shù)據(jù)轉發(fā)業(yè)務2014SatellitebroadbandAfterthe1990s,satellitecommunicationtechnologyhasbeenusedasameanstoconnecttotheInternetviabroadbanddataconnections.Thiscanbeveryusefulforuserswhoarelocatedinveryremoteareas,andcannotaccessawirelinebroadbandordialupconnection.位于邊遠地區(qū)，不能接入有線寬帶網絡或撥號上網。PartIISatelliteInternetaccess22NewWordsterrestrial地面的multicast多播，組播aperture孔徑，光圈distribution分發(fā)interactivity交互switch（電話）交換squawkbox聊天室，論壇queue排隊，隊列priorityqueueing按優(yōu)先級的排序encapsulate封裝outbound向外的ISP互聯(lián)網業(yè)務供應商router路由器proxyserver代理服務器upconverter上變頻器feedline饋線orthomodetransducer直接式收發(fā)轉換器feedhorn饋送電波的喇叭天線23NewWordstermsofcontract合同條款bolt用螺栓固定住costeffective經濟的，合算的surf沖浪，瀏覽網絡authentication認證stack堆棧latency延遲，潛伏期asymmetry不對稱encrypt加密accessible可訪問的，可用的rainfade降雨衰減bidirectional雙向的sponsor支持，贊助，資助architecture結構，建筑241SatelliteInternetservicesareusedinlocationswhereterrestrialInternetaccessisnotavailableandinlocationswhichmovefrequently.Internetaccessviasatelliteisavailableworldwide,includingvesselsatseaandmobilelandvehicles.TherearethreetypesofsatelliteInternetservice:one-waymulticast,one-waywithterrestrialreturn,andverysmallapertureterminal(VSAT)(two-way)satelliteaccess.1

有三種衛(wèi)星因特網服務：單向多播衛(wèi)星接入，地面回傳單向衛(wèi)星接入和甚小口徑（天線）終端（雙向）衛(wèi)星接入。252One-waymulticastOne-waymulticastsatelliteInternetsystemsareusedforInternetProtocol(IP)multicast-baseddata,audioandvideodistribution.IntheU.S.,aFederalCommunicationsCommission(FCC)licenseisrequiredonlyfortheuplinkstationandnolicenseisrequiredforusers.NotethatmostInternetprotocolswillnotworkcorrectlyoverone-wayaccess,sincetheyrequireareturnchannel.

單向多播衛(wèi)星系統(tǒng)用于IP多播數(shù)據(jù)、音頻、視頻的發(fā)布大多數(shù)互聯(lián)網協(xié)議不能在單向接入情況下正常工作，因為它們要求一個回饋信道262However,Internetcontentsuchaswebpagescanstillbedistributedoveraone-waysystemby“pushing”themouttolocalstorageatendusersites,thoughfullinteractivityisnotpossible.ThisismuchlikeTVorradiocontentwhichofferslittleuserinterface.互聯(lián)網內容如Web頁面仍能通過單向系統(tǒng)發(fā)布，這是通過將內容“推”向終端用戶的局域存儲器實現(xiàn)的，盡管不能實現(xiàn)真正的交互性。273Systemhardwarecomponents:Similartoone-wayterrestrialreturn,satelliteInternetaccessmayincludeinterfacestothepublicswitchedtelephonenetworkforsquawkboxapplications.AnInternetconnectionisnotrequired,butmanyapplicationsincludeaFileTransferProtocol(FTP)servertoqueuedataforbroadcast.衛(wèi)星互聯(lián)網接入可包括與公共交換電話網之間的接口用于內部通話。許多應用包括一個FTP服務器以將待廣播的數(shù)據(jù)排成隊列。284Systemsoftwarecomponents:Mostone-waymulticastapplicationsrequirecustomprogrammingattheremotesites.Thesoftwareattheremotesitemustfilter,store,presentaselectioninterfacetoanddisplaythedata.2Thesoftwareatthetransmittingstationmustprovideaccesscontrol,priorityqueueing,sending,andencapsulatingofthedata.遠端的軟件必須對數(shù)據(jù)進行過濾、存儲、提供選擇界面并顯示。數(shù)據(jù)的接入控制、按優(yōu)先級形成隊列、發(fā)送、封裝295One-waywithterrestrialreturnOne-wayterrestrialreturnsatelliteInternetsystemsareusedwithtraditionaldial-upaccesstotheInternet,withoutbounddatatravelingthroughatelephonemodem,butdownloadssentviasatelliteataspeednearthatofbroadbandInternetaccess.IntheUS,anFCClicenseisrequiredfortheuplinkstationonly;nolicenseisrequiredfortheusers.單向地面回傳衛(wèi)星因特網系統(tǒng)與傳統(tǒng)的撥號接入互聯(lián)網一起應用，通過電話modem將數(shù)據(jù)傳出，而通過衛(wèi)星以接近寬帶互聯(lián)網接入的速度進行下載。306SystemhardwarecomponentsThetransmittingstation(alsocalledteleport,headend,uplinkfacility,orhub)hastwocomponents:316Internetconnection:TheISP’sroutersconnecttoproxyserverswhichcanenforcequalityofservice(QoS)bandwidthlimitsandguaranteesforusertraffic.ThesearethenconnectedtoaDVBencapsulatorwhichisthenconnectedtoaDVB-Smodem.Theradiofrequency(RF)signalfromtheDVB-Smodemisconnectedtoanupconverterwhichisconnectedviafeedlinetotheoutdoorunit.3

對用戶流量實行并保證QoS帶寬限制來自DVB-S調制解調器的射頻信號連接到上變頻器，上變頻器通過饋線連接到室外單元。326Satelliteuplink:Theblockupconverter(BUC)andoptionallow-noiseblockconverter(LNB),whichmayuseawaveguidetoconnecttotheoptionalorthomodetransducer(OMT)whichisboltedtothefeedhornwhichisconnectedbymetalsupportstothesatellitedishandmount.用波導聯(lián)到一個接在饋電喇叭上的可選直接式收發(fā)轉換器，它被用金屬支撐安裝在衛(wèi)星天線和支架上。337Attheremotelocation(Earthstation)thesetupconsistsof:Outdoorunit(satellitedishwithmount,feedhorn,universalLNBforKuband,andfeedline)Indoorunit(DVB-SPeripheralComponentInterconnectcardinsideacomputer,orDVBexternalmodemconnectedtoacomputerviaanEthernetportorUSBport)348Dependingontheprovider’stermsofcontract,onecosteffectivewaytouseone-waysatelliteinternetistouseGeneralPacketRadioService(GPRS)fortheback-channel.Byutilizinga9600bit/sconnectionthatisofferedinstandardGPRS,theuploadvolumeisverylow,andsincethisserviceisnotper-timecharged,butchargedbyvolumeuploaded,usersareabletosurfanddownloadinbroadbandspeeds.4

通過使用標準GPRS提供的9600bps連接，上傳量很小。此外由于該項業(yè)務不是按時間計費，而是按上傳數(shù)據(jù)流量計費的，用戶可以寬帶速度進行瀏覽和下載。358Therearecompaniesofferingspeedupto24Mbit/s.AnotherviewofusingGPRSasreturnwouldbethemobilitywhentheserviceisprovidedbyasatellitethattransmitsinthefieldof50to53dBW.Usinga33cmwidesatellitedish,anotebookandanormalGPRSequippedGSMphone,userscangetbroadbandeverywhere.用GPRS作為回傳的另一個理由是由衛(wèi)星提供業(yè)務時的機動性，衛(wèi)星發(fā)射場在50dBW到53dBW之間。TheDecibelwattordBWisaunitforthemeasurementofthestrengthofasignalexpressedindecibelsrelativetoonewatt.369SystemsoftwarecomponentsRemotesitesrequireaminimumofprogrammingtoprovideauthenticationandsetproxyserversettings.FilteringisusuallyprovidedbytheDVBcarddriver.遠程節(jié)點在提供認證和設置代理服務器時要求最少的編程3710Often,non-standardIPstacksareusedtoaddressthelatencyandasymmetryproblemsofthesatelliteconnection.Datasentoverthesatellitelinkisgenerallyencrypted,asotherwiseitwouldbeaccessibletoanyonewithasatellitereceiver.用非標準IP堆棧解決衛(wèi)星連接中的潛伏期和非對稱問題。3811ManyIP-over-satelliteimplementationsusepairedproxyserversatbothendpointssothatclientsandserversdonotneedtoacceptthelatencyinherentinasatelliteconnection.5

許多衛(wèi)星IP的實現(xiàn)在終端使用成對的代理服務器，這樣客戶端和服務器就不必承受衛(wèi)星連接中固有的延遲。3911Forsimilarreasons,thereexistspecialVirtualPrivateNetwork(VPN)implementationsdesignedforuseoversatellitelinksbecausestandardVPNsoftwarecannothandlethelongpackettraveltimes.4012Uploadspeedsarelimitedbytheuser’sdial-upmodem,andlatencyishigh,asitisforanysatellitebasedInternet.Downloadspeedscanbeveryfastcomparedtodial-up:1

Mbit/s,4

Mbit/s,and16

Mbit/spackagesaregenerallyoffered.上傳速度受制于用戶的撥號modem，延遲量很大，對任何基于衛(wèi)星的互聯(lián)網業(yè)務都是如此。4113TheoryofoperationThebackpanelofasatellitemodem,withcoaxialconnectionsforbothingandoutgoingsignals,andanEthernetportforconnectiontotheinternalnetwork.4214Remotesitesusetheproxyserverattheearthstation,whichisconfiguredtoroutealloutboundtraffictotheQoSserver,whichmakessurenouserexceedstheallottedbandwidthormonthlytrafficlimits.6Trafficisthensenttotheencapsulator,whichputstheIPpacketsinsideofDVBpackets.TheDVBpacketsarethensenttotheDVBmodemandthentothetransmitter.在地面發(fā)送站遠地使用代理服務器，其設定為向服務質量服務器發(fā)送所有的外傳數(shù)據(jù)，服務質量服務器確保用戶不超過分配帶寬或每月的通信流量限制。4315Two-wayTwo-waysatelliteInternetservicesendsdatafromremotesitesviasatellitetoahub,whichthensendsthedatatotheInternet.Thesatellitedishateachlocationmustbepreciselypositionedtoavoidinterferencewithothersatellites.Theoscillatorsinsomeradardetectorscancauseinterferencewiththesesystems.雙向衛(wèi)星業(yè)務通過衛(wèi)星向Hub傳送數(shù)據(jù)，Hub又將數(shù)據(jù)傳向衛(wèi)星。4415Also,eachlocationmustusepowermanagementtoadjusttheamountoftransmitpowertocompensateforthingslikerainfade.Thereareseveraltype