信號(hào)系統(tǒng)與電子線路-復(fù)試專業(yè)英語

TechnicalEnglishForInformationScienceandElectronicEngineeringUnit7SatelliteCommunicationsPartIApplicationsofCommunicationssatellite3NewWordsabbreviate縮略，簡寫成geostationaryorbit對(duì)地靜止軌道ellipticalorbit橢圓軌道complementary互補(bǔ)的，補(bǔ)充的submarine海底的，潛水艇relay中繼，接力analogous模擬的，類似的disturbance擾動(dòng)，干擾constellation星座圖，星羅棋布geosynchronous地球同步的affiliate會(huì)員，分支機(jī)構(gòu)limelight眾人注目的中心diameter直徑free-to-airTV不加密不收費(fèi)電視headend數(shù)據(jù)轉(zhuǎn)發(fā)器ambiguous模糊的，混淆的transponder轉(zhuǎn)發(fā)器，應(yīng)答器space-bornerepeater天空轉(zhuǎn)發(fā)器amateur業(yè)余愛好，業(yè)余的dialup撥號(hào)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(duì)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(jī)和手持終端的移動(dòng)通信，用于電視和無線電廣播，以及應(yīng)用其它技術(shù)，比如電纜，是不現(xiàn)實(shí)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(duì)地靜止衛(wèi)星上73Ananalogouspathisthenfollowedonthedownlink.Incontrast,mobiletelephones(toandfromshipsandairplanes)mustbedirectlyconnectedtoequipmenttouplinkthesignaltothesatellite,aswellasbeingabletoensuresatellitepointinginthepresenceofdisturbances,suchaswavesonboardaship.2相反，移動(dòng)電話（船和飛機(jī)上接收和發(fā)送的）必須直接連到設(shè)備把信號(hào)上傳到衛(wèi)星，又能確保在有干擾時(shí)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(jìn)導(dǎo)致了20世紀(jì)后期用于固定電話的衛(wèi)星應(yīng)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(duì)相對(duì)很少的大帶寬信號(hào)同時(shí)傳送給很多接收機(jī)的要求更好地匹配了對(duì)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(wǎng)和加盟地方臺(tái)饋送或收集廣播節(jié)目，也用于中小學(xué)和大學(xué)的遠(yuǎn)程教學(xué)、商業(yè)電視、視頻會(huì)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(wù)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(shù)在DTH節(jié)目方面的風(fēng)頭1510Free-to-airsatelliteTVchannelsarealsousuallydistributedonFSSsatellitesintheKuband.TheIntelsatAmericas5,Galaxy10RandAMC3satellitesoverNorthAmerica

provideaquitelargeamountofFTAchannels

ontheirKubandtransponders.在他們的Ku波段收發(fā)器上提供相當(dāng)多的FTA頻道。1611TheAmericanDishNetworkDBSservicehasalsousedFSStechnologyduetotheirneedformorecapacitytocarrylocaltelevisionstations,andformorebandwidthtocarryHDTVchannels.SatellitesforcommunicationhavenowbeenlaunchedthathavetranspondersintheKaband.NASAaswellhaslaunchedexperimentalsatellitesusingtheKabandrecently.由于傳輸?shù)胤诫娨暸_(tái)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(jí)同樣級(jí)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(shè)計(jì)成承載業(yè)余無線電通信流量通常被裝備UHF或VHF設(shè)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(shè)計(jì)得只能在任何給定時(shí)刻進(jìn)行有限次數(shù)的簡短接觸。數(shù)據(jù)轉(zhuǎn)發(fā)業(yè)務(wù)2014SatellitebroadbandAfterthe1990s,satellitecommunicationtechnologyhasbeenusedasameanstoconnecttotheInternetviabroadbanddataconnections.Thiscanbeveryusefulforuserswhoarelocatedinveryremoteareas,andcannotaccessawirelinebroadbandordialupconnection.位于邊遠(yuǎn)地區(qū)，不能接入有線寬帶網(wǎng)絡(luò)或撥號(hào)上網(wǎng)。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(duì)，隊(duì)列priorityqueueing按優(yōu)先級(jí)的排序encapsulate封裝outbound向外的ISP互聯(lián)網(wǎng)業(yè)務(wù)供應(yīng)商router路由器proxyserver代理服務(wù)器upconverter上變頻器feedline饋線orthomodetransducer直接式收發(fā)轉(zhuǎn)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(jīng)濟(jì)的，合算的surf沖浪，瀏覽網(wǎng)絡(luò)authentication認(rèn)證stack堆棧latency延遲，潛伏期asymmetry不對(duì)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(jié)構(gòu)，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(wǎng)服務(wù)：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(wǎng)協(xié)議不能在單向接入情況下正常工作，因?yàn)樗鼈円笠粋€(gè)回饋信道262However,Internetcontentsuchaswebpagescanstillbedistributedoveraone-waysystemby“pushing”themouttolocalstorageatendusersites,thoughfullinteractivityisnotpossible.ThisismuchlikeTVorradiocontentwhichofferslittleuserinterface.互聯(lián)網(wǎng)內(nèi)容如Web頁面仍能通過單向系統(tǒng)發(fā)布，這是通過將內(nèi)容“推”向終端用戶的局域存儲(chǔ)器實(shí)現(xiàn)的，盡管不能實(shí)現(xiàn)真正的交互性。273Systemhardwarecomponents:Similartoone-wayterrestrialreturn,satelliteInternetaccessmayincludeinterfacestothepublicswitchedtelephonenetworkforsquawkboxapplications.AnInternetconnectionisnotrequired,butmanyapplicationsincludeaFileTransferProtocol(FTP)servertoqueuedataforbroadcast.衛(wèi)星互聯(lián)網(wǎng)接入可包括與公共交換電話網(wǎng)之間的接口用于內(nèi)部通話。許多應(yīng)用包括一個(gè)FTP服務(wù)器以將待廣播的數(shù)據(jù)排成隊(duì)列。284Systemsoftwarecomponents:Mostone-waymulticastapplicationsrequirecustomprogrammingattheremotesites.Thesoftwareattheremotesitemustfilter,store,presentaselectioninterfacetoanddisplaythedata.2Thesoftwareatthetransmittingstationmustprovideaccesscontrol,priorityqueueing,sending,andencapsulatingofthedata.遠(yuǎn)端的軟件必須對(duì)數(shù)據(jù)進(jìn)行過濾、存儲(chǔ)、提供選擇界面并顯示。數(shù)據(jù)的接入控制、按優(yōu)先級(jí)形成隊(duì)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(wǎng)系統(tǒng)與傳統(tǒng)的撥號(hào)接入互聯(lián)網(wǎng)一起應(yīng)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(wǎng)接入的速度進(jìn)行下載。306SystemhardwarecomponentsThetransmittingstation(alsocalledteleport,headend,uplinkfacility,orhub)hastwocomponents:316Internetconnection:TheISP’sroutersconnecttoproxyserverswhichcanenforcequalityofservice(QoS)bandwidthlimitsandguaranteesforusertraffic.ThesearethenconnectedtoaDVBencapsulatorwhichisthenconnectedtoaDVB-Smodem.Theradiofrequency(RF)signalfromtheDVB-Smodemisconnectedtoanupconverterwhichisconnectedviafeedlinetotheoutdoorunit.3

對(duì)用戶流量實(shí)行并保證QoS帶寬限制來自DVB-S調(diào)制解調(diào)器的射頻信號(hào)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(dǎo)聯(lián)到一個(gè)接在饋電喇叭上的可選直接式收發(fā)轉(zhuǎn)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(biāo)準(zhǔn)GPRS提供的9600bps連接，上傳量很小。此外由于該項(xiàng)業(yè)務(wù)不是按時(shí)間計(jì)費(fèi)，而是按上傳數(shù)據(jù)流量計(jì)費(fèi)的，用戶可以寬帶速度進(jìn)行瀏覽和下載。358Therearecompaniesofferingspeedupto24Mbit/s.AnotherviewofusingGPRSasreturnwouldbethemobilitywhentheserviceisprovidedbyasatellitethattransmitsinthefieldof50to53dBW.Usinga33cmwidesatellitedish,anotebookandanormalGPRSequippedGSMphone,userscangetbroadbandeverywhere.用GPRS作為回傳的另一個(gè)理由是由衛(wèi)星提供業(yè)務(wù)時(shí)的機(jī)動(dòng)性，衛(wèi)星發(fā)射場在50dBW到53dBW之間。TheDecibelwattordBWisaunitforthemeasurementofthestrengthofasignalexpressedindecibelsrelativetoonewatt.369SystemsoftwarecomponentsRemotesitesrequireaminimumofprogrammingtoprovideauthenticationandsetproxyserversettings.FilteringisusuallyprovidedbytheDVBcarddriver.遠(yuǎn)程節(jié)點(diǎn)在提供認(rèn)證和設(shè)置代理服務(wù)器時(shí)要求最少的編程3710Often,non-standardIPstacksareusedtoaddressthelatencyandasymmetryproblemsofthesatelliteconnection.Datasentoverthesatellitelinkisgenerallyencrypted,asotherwiseitwouldbeaccessibletoanyonewithasatellitereceiver.用非標(biāo)準(zhǔn)IP堆棧解決衛(wèi)星連接中的潛伏期和非對(duì)稱問題。3811ManyIP-over-satelliteimplementationsusepairedproxyserversatbothendpointssothatclientsandserversdonotneedtoacceptthelatencyinherentinasatelliteconnection.5

許多衛(wèi)星IP的實(shí)現(xiàn)在終端使用成對(duì)的代理服務(wù)器，這樣客戶端和服務(wù)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(hào)modem，延遲量很大，對(duì)任何基于衛(wèi)星的互聯(lián)網(wǎng)業(yè)務(wù)都是如此。4113TheoryofoperationThebackpanelofasatellitemodem,withcoaxialconnectionsforbothingandoutgoingsignals,andanEthernetportforconnectiontotheinternalnetwork.4214Remotesitesusetheproxyserverattheearthstation,whichisconfiguredtoroutealloutboundtraffictotheQoSserver,whichmakessurenouserexceedstheallottedbandwidthormonthlytrafficlimits.6Trafficisthensenttotheencapsulator,whichputstheIPpacketsinsideofDVBpackets.TheDVBpacketsarethensenttotheDVBmodemandthentothetransmitter.在地面發(fā)送站遠(yuǎn)地使用代理服務(wù)器，其設(shè)定為向服務(wù)質(zhì)量服務(wù)器發(fā)送所有的外傳數(shù)據(jù)，服務(wù)質(zhì)量服務(wù)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(wù)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