Digital modulation overview

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1、WSSG-RF/IFSystemDesignDigitalModulationOverviewDigitalModulationOverviewAlbertH.Higashi(602)413-5309RevisedonJune23,1998MOTOROLACONFIDENTIALPROPRIETARY-8/6/98AlbertHigashi(602)413-5309SemiconductorProductsSectorWSSG-RF/IFSystemDesignNotesTb=BitTimeTs=SymbolTime=Tb*(Bitspersymbol)BitRate=1/T=RbbSy

2、mbolRate=1/T=RssWithrespecttothefollowingexampleswhichuseaRaised-Cosineresponseasthebandlimitingtransmitfilter,theactualimplementationwouldemployasquare-RootRaised-CosinefilteronthetransmitterandanidenticalfilterforthereceiverwhichwouldhaveacompositeresponseofaRaised-Cosinefilter.Thereasonfordoin

3、gsoisthatRaised-CosinefiltersbelongtotheNyquistclassoffilters(Zero-ISI)andtheobjectiveistoreceiveazero-ISIsignalafterthematchedfilter(noiserejection),sotheoptimalsolutionistosplittheresponsebetweenthetransmitterandthereceiver.EyePatternsarediagramexamplesofanoscilloscopeoutputifasignalistriggered

4、withaclockatthesymbolrate.Thisdiagramisusefulindeterminingoptimalsampletimesfordataslicing/estimation.InexponentialFourierseries,thebasisfunctionsareexponentialsnot1jnwwoot-jntsinusoids.Therefore,spectrumsofrealsignalsexistovernegativeaswellcosntw=+[ee]o2aspositivefrequenciesbecausetheexponential

5、indexisreferredtoasthefrequencyofthatcomponent.MOTOROLACONFIDENTIALPROPRIETARY-8/6/98AlbertHigashi(602)413-5309SemiconductorProductsSector2WSSG-RF/IFSystemDesignModulation•Analog–AM»Double-Sideband»Single-Sideband–FM•Digital–Linear–Non-LinearMOTOROLACONFIDENTIALPROPRIETARY-8/6/98AlbertHigashi(602

6、)413-5309SemiconductorProductsSector3WSSG-RF/IFSystemDesignAmplitudeModulation(AM)AmplitudeModulation(AM)Double-Sideband-Suppressed-Carrier(DSB-SC)m(t)coswtm(t)«M(w)m(t)c(Ac=1)m(t)coswt«½[M(w+w)+M(w-w)]cccBasebandBWisB.NegativeInAmplitudeModulation,theamplitudeofAccoswctfrequencycomponentistheunm

7、odulatedcarrierisvariedproductofFourierseriesproportionallytothemodulatingsignalm(t).expansion.M(w)ThebandwidthofthemodulatedsignalisNoDCsignal®NoCarrier2B(twicethatofthebasebandsignalm(t)).m(t)Themodulatedsignalspectr