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.Theswitchesformanelectricalconnectionbetweenthetwousersandthesettingoftheseswitchesisdeterminedelectronic

2、allywhenthecallerdialsthenumber.Oncetheconnectionismade,thecaller'svoiceistransformedtoanelectricalsignalusingasmallmicrophoneinthecaller'shandset.Thiselectricalsignalisthensentthroughthenetworktotheuserattheotherendwhereittransformedbackintosoundbyasmallspeakerinthatper

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

4、loguesignals,increasinglytelephoneserviceprovidersaretransparentlyconvertingthesignalstodigitalfortransmissionbeforeconvertingthembacktoanalogueforreception.Theadvantageofthisisthatdigitizedvoicedatacantravelside-by-sidewithdatafromtheInternetandcanbeperfectlyreproducedi

5、nlongdistancecommunication(asopposedtoanaloguesignalsthatareinevitablyimpactedbynoise).Mobilephoneshavehadasignificantimpactontelephonenetworks.Mobilephonesubscriptionsnowoutnumberfixed-linesubscriptionsinmanymarkets.Salesofmobilephonesin2005totalled816.6millionwiththatf

6、igurebeingalmostequallysharedamongstthemarketsofAsia/Pacific(204m),WesternEurope(164m),CEMEA(CentralEurope,theMiddleEastandAfrica)(153.5m),NorthAmerica(148m)andLatinAmerica(102m).Intermsofnewsubscriptionsoverthefiveyearsfrom1999,Africahasoutpacedothermarketswith58.2%grow

7、th.Increasinglythese-7--phonesarebeingservicedbysystemswherethevoicecontentistransmitteddigitallysuchasGSMorW-CDMAwithmanymarketschoosingtodepreciateanaloguesystemssuchasAMPS.Therehavealsobeendramaticchangesintelephonecommunicationbehindthescenes.Startingwiththeoperation

8、ofTAT-8in1988,the1990ssawthewidespreadadoptionofsystemsbasedonopticfibres.Thebenefitofcommunicatingwith