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1、毕业设计(论文)外文资料翻译系别:电子信息系专业:通信工程班级:姓名:学号:外文出处:网络资源附件:1.原文;2.译文2013年03月DigitalCommunications1INTRODUCTIONInthisbook,wepresentthebasicprinciplesthatunderlietheanalysisanddesignofdigitalcommunicationsystems.Thesubjectofdigitalcommunicationsinvolvesthetransmissionofin
2、formationindigitalformfromasourcethatgeneratestheinformationtooneormoredestinations.Ofparticularimportanceintheanalysisanddesignofcommunicationsystemsarethecharacteristicsofthephysicalchannelsthroughwhichtheinformationistransmitted.Thecharacteristicsofthechanne
3、lgenerallyaffectthedesignofthebasicbuildingblocksofthecommunicationsystem.Below,wedescribetheelementsofacommunicationsystemandtheirfunctions.1.1ELEMENTSOFADIGITALCOMMUNICATIONSYSTEMFigure1.1illustratesthefunctionaldiagramandthebasicelementsofadigitalcommunicati
4、onsystem.Thesourceoutputmaybeeitherananalogsignal,suchasaudioorvideosignal,oradigitalsignal,suchastheoutputofateletypemachine,thatisdiscreteintimeandhasafinitenumberofoutputcharacters.Inadigitalcommunicationsystem,themessagesproducedbythesourceareconvertedintoa
5、sequenceofbinarydigits.Ideally,weshouldliketorepresentthesourceoutput(message)byasfewbinarydigitsaspossible.Inotherwords,weseekanefficientrepresentationofthesourceoutputthatresultsinlittleornoredundancy.Theprocessofefficientlyconvertingtheoutputofeitherananalog
6、ordigitalsourceintoasequenceofbinarydigitsiscalledsourceencodingordatacompression.Thesequenceofbinarydigitsfromthesourceencoder,whichwecalltheinformationsequence,ispassedlothechannelencoder.Thepurposeofthechannelencoderistointroduce,inacontrolledmanner,someredu
7、ndancyinthebinaryinformationsequencethatcanbeusedatthereceivertoovercometheeffectsofnoiseandinterferenceencounteredinthetransmissionofthesignalthroughthechannel.Thus,theaddedredundancyservestoincreasethereliabilityofthereceiveddataandimprovesthefidelityoftherec
8、eivedsignal.Ineffect,redundancyintheinformationsequenceaidsthereceiverindecodingthedesiredinformationsequence.Forexample,a(trivial)formofencodingofthebinaryinformationsequen