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1、基带信号的码型（Codetypeofbasebandsignal）basebandsignalThereceivedsignalisdemodulatedbeforethedemodulationoftheradiofrequencysignal,andthetransmittedsignalbeforethemodulationiscoded,i.e.thecodedbutnotmodulatedsignalatthetimeoftransmitting.It'scommonlycalledI,Qsignals.Butinfact,becauseofthedevelopmentofch
2、iptechnology,basebandsignalsaretransmittedinthemachineboardintheformofdatastream,suchasV70,etc.....YouTektronixoscilloscopemeasuredisnotbasebandsignal,jumpDClevel,basebandsignalfrequencyis67KHz,Samsung600mobilephonesinthemostobvioustest.Again:digitaloscilloscopehasnoanaloggooduseinmobilephones,es
3、peciallyintheobservationofabruptsignals.4.1codetypeofdigitalbasebandsignal4.1codetypeofdigitalbasebandsignalThemainpointsofthissection:Codedesignprincipleofdigitalbasebandsignals,commoncodetypedigitalbasebandsignalpowerspectrumCodedesignprincipleof4.1.1digitalbasebandsignalTheso-calleddigitalbase
4、bandsignalistheelectricpulserepresentationofthemessagecode--theelectricwaveform.Inthebasebandtransmissionsystem,theoriginaldigitalbasebandsignalnotallcantransmitinthechannel,forexample,thebasebandsignalisrichinDCandlowfrequencycomponentisnotsuitablefortransmissioninthechannel,becauseitmaycauseser
5、iousdistortionofthesignal;forexample,thegeneralbasebandtransmissionsystemisabitsynchronoussignalfromthereceivedsignal,codeandbitsynchronizationsignalisdependentonthecode,ifthecodehasalongtime."0"symbol,thebasebandsignalmayappearfor0timeTherefore,thebitsynchronizationrecoverysystemcannotguaranteet
6、heaccuracyofbitsynchronizationsignals.Theactualbasebandtransmissionsystemmayalsoputforwardotherrequirements,resultinginvariouspossiblerequirementsforbasebandsignals.Tosumup,therearetwomainrequirementsforbasebandsignalsfortransmission:(1)therequirementofvariouscodesisexpectedtobecompiledintothecod
7、etypesuitablefortransmission;(2Therequirementoftheradioshapeoftheselectedcodepatternisexpectedthattheradiowaveshapeissuitablefortransmissioninthechannel.Theformerproblemiscalledthechoiceofthetransmissioncode,andthelatt
