数字通信中英文翻译_学位论文.doc

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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.Thesubjectofdigitalcommunicationsinvolvesthetransmissionofinformationindigitalformfromasour

2、cethatgeneratestheinformationtooneormoredestinations.Ofparticularimportanceintheanalysisanddesignofcommunicationsystemsarethecharacteristicsofthephysicalchannelsthroughwhichtheinformationistransmitted.Thecharacteristicsofthechannelgenerallyaffectthedesignofthebasicbuildingblocksofthecommunic

3、ationsystem.Below,wedescribetheelementsofacommunicationsystemandtheirfunctions.1.1ELEMENTSOFADIGITALCOMMUNICATIONSYSTEMFigure1.1illustratesthefunctionaldiagramandthebasicelementsofadigitalcommunicationsystem.Thesourceoutputmaybeeitherananalogsignal,suchasaudioorvideosignal,oradigitalsignal,s

4、uchastheoutputofateletypemachine,thatisdiscreteintimeandhasafinitenumberofoutputcharacters.Inadigitalcommunicationsystem,themessagesproducedbythesourceareconvertedintoasequenceofbinarydigits.Ideally,weshouldliketorepresentthesourceoutput(message)byasfewbinarydigitsaspossible.Inotherwords,wes

5、eekanefficientrepresentationofthesourceoutputthatresultsinlittleornoredundancy.Theprocessofefficientlyconvertingtheoutputofeitherananalogordigitalsourceintoasequenceofbinarydigitsiscalledsourceencodingordatacompression.Thesequenceofbinarydigitsfromthesourceencoder,whichwecalltheinformationse

6、quence,ispassedlothechannelencoder.Thepurposeofthechannelencoderistointroduce,inacontrolledmanner,someredundancyinthebinaryinformationsequencethatcanbeusedatthereceivertoovercometheeffectsofnoiseandinterferenceencounteredinthetransmissionofthesignalthroughthechannel.Thus,theaddedredundancyse

7、rvestoincreasethereliabilityofthereceiveddataandimprovesthefidelityofthereceivedsignal.Ineffect,redundancyintheinformationsequenceaidsthereceiverindecodingthedesiredinformationsequence.Forexample,a(trivial)formofencodingofthebinaryinformationsequen