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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
