电子通信专业 外文翻译 外文文献 英文文献 电信现代运营

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1、毕业设计（外文翻译材料）TelecommunicationModernOperationTelephoneInananaloguetelephonenetwork,thecallerisconnectedtothepersonhewantstotalktobyswitchesatvarioustelephoneexchanges.Theswitchesformanelectricalconnectionbetweenthetwousersandthesettingoftheseswitchesisdeterminedelectroni

2、callywhenthecallerdialsthenumber.Oncetheconnectionismade,thecaller'svoiceistransformedtoanelectricalsignalusingasmallmicrophoneinthecaller'shandset.Thiselectricalsignalisthensentthroughthenetworktotheuserattheotherendwhereittransformedbackintosoundbyasmallspeakerinthatp

3、erson'shandset.Thereisaseparateelectricalconnectionthatworksinreverse,allowingtheuserstoconverse.Thefixed-linetelephonesinmostresidentialhomesareanalogue—thatis,thespeaker'svoicedirectlydeterminesthesignal'svoltage.Althoughshort-distancecallsmaybehandledfromend-to-endas

4、analoguesignals,increasinglytelephoneserviceprovidersaretransparentlyconvertingthesignalstodigitalfortransmissionbeforeconvertingthembacktoanalogueforreception.Theadvantageofthisisthatdigitizedvoicedatacantravelside-by-sidewithdatafromtheInternetandcanbeperfectlyreprodu

5、cedinlongdistancecommunication(asopposedtoanaloguesignalsthatareinevitablyimpactedbynoise).Mobilephoneshavehadasignificantimpactontelephonenetworks.Mobilephonesubscriptionsnowoutnumberfixed-linesubscriptionsinmanymarkets.Salesofmobilephonesin2005totalled816.6millionwith

6、thatfigurebeingalmostequallysharedamongstthemarketsofAsia/Pacific(204m),WesternEurope(164m),CEMEA(CentralEurope,theMiddleEastandAfrica)(153.5m),NorthAmerica(148m)andLatinAmerica(102m).Intermsofnewsubscriptionsoverthefiveyearsfrom1999,Africahasoutpacedothermarketswith58.

7、2%growth.Increasinglythese-6--phonesarebeingservicedbysystemswherethevoicecontentistransmitteddigitallysuchasGSMorW-CDMAwithmanymarketschoosingtodepreciateanaloguesystemssuchasAMPS.Therehavealsobeendramaticchangesintelephonecommunicationbehindthescenes.Startingwiththeop

8、erationofTAT-8in1988,the1990ssawthewidespreadadoptionofsystemsbasedonopticfibres.Thebenefitofcommunicatingwith