无线通信基础(双语)-教学课件-7PPT资料.ppt

无线通信基础(双语)-教学课件-7PPT资料.ppt

《无线通信基础(双语)-教学课件-7PPT资料.ppt》由会员分享，可在线阅读，更多相关《无线通信基础(双语)-教学课件-7PPT资料.ppt（55页珍藏版）》请在冰点文库上搜索。

Lineartime-variantchannelmodelChannelImpulseResponseTime-VariantTransferFunctionDopplerSpreadFunctionDelay-Dopplerspreadfunction,ReviewofLastClass,ReviewofLastClass,Example2.11LTVChannelModel,ConsideranLTVchannelwithimpulseresponsegivenbyWhereT=0.1ms,and.（a）Findthechanneltime-varianttransferfunctionandtheDopplerspreadfunction（b）GiventhatthetransmittedsignalisWhereT0=0.025ms,findthereceivedsignalintheabsenceofbackgroundnoise.,（c）Repeatpart（b）ifthetransmittedsignalisWhereT1=0.05ms（d）Whatdoyouobservefromtheresultsofparts（b）and（c）?

@#@,ConsideranLTVchannelwithimpulseresponsegivenbyWhereT=0.1ms,and.,Example2.11LTVChannelModel,Whenthechannelchangeswithtimerandomly,thechannelfunctionsarerandomprocessedandaredifficulttocharacterize.Undertheassumptionthattherandomprocesseshavezeromean,weareinterestedinthecorrelationfunctionsoftherandomprocesses.,Forsimplicityofanalysis,weassumethat（a）Thechannelimpulseresponseisawide-sensestationary（WSS）process（b）Thechannelimpulsesatandareuncorrelatedifforanyt.,Achannelunderassumptions（a）and（b）issaidtobeawide-sensestationaryuncorrelatedscattering（WSSUS）channel.,Chapter2-Lecture6,Channelcorrelationfunctions,2.3Channelcorrelationfunctions,2.3.2FrequencyandTimeCorrelationFunction,2.3.4Examples,2.3.1DelayPowerSpectralDensity,2.3.3DopplerPowerSpectralDensity,2.3Channelcorrelationfunctions,1、DelayPowerSpectralDensity,TheDefinitionoftheDelayPSDStatisticsDescribingtheDelayPSD,Underassumption（a）,theautocorrelationfunctionofdefineas,Whichisafunctionof,and,anddoesnotdependont.,TheDefinitionoftheDelayPSD,1、DelayPowerSpectralDensity,Thecorrelationfunctioncanberepresentedas,Underassumption（b）,theautocorrelationfunctioncanberepresentedintheform,1、DelayPowerSpectralDensity,TheDefinitionoftheDelayPSD,orequivalently,where,1、DelayPowerSpectralDensity,TheDefinitionoftheDelayPSD,Att=0,wedefine,Thus,wehave,1、DelayPowerSpectralDensity,TheDefinitionoftheDelayPSD,AccordingtotheWiener-Khintchinerelations,thefunctionrepresentspowerspectraldensity（PSD）.ItmeasurestheaveragePSDatthechanneloutputasafunctionofthepropagationdelay,andisthereforecalledthedelayPSDofthechannel,alsoknownasthemultipathintensityprofile.,WeobservethatistheFouriertransformofthecorrelationfunction.,1、DelayPowerSpectralDensity,TheDefinitionoftheDelayPSD,ThenominalwidthofthedelayPSDpulseiscalledthemultipathdelayspread,denotedbyTm,1、DelayPowerSpectralDensity,TheDefinitionoftheDelayPSD,Thenthmomentofthedelay,denotedby,isgivenby,1、DelayPowerSpectralDensity,StatisticsDescribingtheDelayPSD,Themeanpropagationdelay,denotedby,TheRMSdelayspread,denotedby,1、DelayPowerSpectralDensity,StatisticsDescribingtheDelayPSD,Incalculatingavalueforthemultipathdelayspread,itisusuallyassumedthat,1、DelayPowerSpectralDensity,StatisticsDescribingtheDelayPSD,1、DelayPowerSpectralDensity,1、DelayPowerSpectralDensity,Example2.12Fromexample2.9,findtheDelayPSD,1、DelayPowerSpectralDensity,Example2.12Fromexample2.9,findtheDelayPSD,1、DelayPowerSpectralDensity,Example2.13,calculatethermsdelayspreadforthetwo-pathpowerdelayprofile#1.t0=0,p0=0dB.#2.t1=1s,p1=0dB,1、DelayPowerSpectralDensity,Lineartime-variantchannelmodelChannelImpulseResponseTime-VariantTransferFunctionDopplerSpreadFunctionDelay-Dopplerspreadfunction,ReviewofLastClass,ReviewofLastClass,ReviewofLastClass,TheDefinitionoftheDelayPSD,ReviewofLastClass,StatisticsDescribingtheDelayPSD,2.3Channelcorrelationfunctions,2、Frequencyandtimecorrelationfunction,FrequencycorrelationfunctionTimecorrelationfunction,Fromtherelationshipbetweenand,wehavethefollowing:

@#@a）IfisWSS,thenisalsoWSSwithrespecttot.Asaresult,wecandefinetheautocorrelationfunctionofthetime-varianttransferfunctionas,2、Frequencyandtimecorrelationfunction,Fromtherelationshipbetweenand,wehavethefollowing:

@#@,where,Time-frequencycorrelationfunction,b）Thecorrelationfunctioncanberepresentedintermofthecorrelationfunction,2、Frequencyandtimecorrelationfunction,Letting,Thenominalwidthof,denotedby,iscalledthechannelcoherencebandwidth.,2、Frequencyandtimecorrelationfunction,Frequencycorrelationfunction,Sincetimeandfrequencyhaveaninverserelationship,wehave,2、Frequencyandtimecorrelationfunction,Frequencycorrelationfunction,LetWsdenotethebandwidthofthetransmittedsignal,thefadingchannelcanbegrosslycategorizedasfollows:

@#@,If,thechannelissaidtoexhibitfrequencyselectivefadingwhichintroducessevereISItothereceivedsignalIf,thechannelissaidtoexhibitfrequencynonselectivefadingorflatfadingwhichintroducesnegligibleISI,2、Frequencyandtimecorrelationfunction,Frequencycorrelationfunction,Inthetime-frequencycorrelationfunctionletting,Itcharacterizes,onaverage,howfastthechanneltransferfunctionchangeswithtimeateachfrequency.,2、Frequencyandtimecorrelationfunction,Timecorrelationfunction,Thenominalwidthof,denotedby,iscalledthechannelcoherencetime.,2、Frequencyandtimecorrelationfunction,Timecorrelationfunction,IfthechannelcoherencetimeismuchlargerthanthesymbolintervalofthetransmittedsignalslowfadingIfthechannelcoherencetimeissmallerthanthesymbolintervalofthetransmittedsignalfastfading,2、Frequencyandtimecorrelationfunction,Timecorrelationfunction,ThecorrelationfunctionoftheDopplerspreadfunctionisdefinedas,ForaWSSUSchannel,thecorrelationfunctioncanberepresentedintheform,2.3Channelcorrelationfunctions,3、DopplerPowerSpectralDensity,canbeobtainedbyFouriertransformationofthefrequency-timecorrelationfunctionwithrespectto.Therefore,At,wehave,3、DopplerPowerSpectralDensity,Thenominalwidthof,denotedby,iscalledtheDopplerspread.,3、DopplerPowerSpectralDensity,DopplerPSD,ThemeanDopplershift,denotedby,TheRMSDopplershift,denotedby,DopplerPSD,3、DopplerPowerSpectralDensity,Relationshipsbetweenthechannelcorrelationfunctionsandbetweenthechannelparameters,2.3Channelcorrelationfunctions,2.3Channelcorrelationfunctions,Wecandefine4basicfadingtypes2basicfadingtypesduetomultipathdelayspread:

@#@flatfading,frequencyselectivefading2basicfadingtypesduetoDopplerspread:

@#@fastfading,slowfadingWecandefine4compositefadingtypesFlat/frequencyselectiveareindependentoffast/slowfadingSoassimplecombination:

@#@fastflatfading,slowflatfading,fastfrequencyselectivefading,slowfrequencyselectivefading,2.3Channelcorrelationfunctions,FlatfadingChannelhasconstantgain&@#@linearphaseresponseoverabandwidthgreaterthanthesignalbandwidthReceivedsignalstrengthmaybedifferent,butnochangeinspectrum（waveformshape）Requirements:

@#@Example:

@#@whenthereisonlyonepathModeledasasingle-tapchannel:

@#@gainchangesrandomly,maycausedeepfades,2.3Channelcorrelationfunctions,BasicType1.FlatFading,Flatfadingillustration:

@#@time&@#@frequencyresponseofflatfadingchannel,2.3Channelcorrelationfunctions,BasicType1.FlatFading,FrequencyselectivefadingChannelhasdifferentgainswithinthebandwidthofthesignalRequirement:

@#@Multipathdelayspreadlongerthansymbolperiodintroduceinter-symbolinterference（ISI）ISI（timedomain）differentgains（frequency）Modeledasstatisticallinearfilterchannelswithrandom,timevaryingcoefficients,2.3Channelcorrelationfunctions,BasicType2.Frequency-SelectiveFading,FrequencyselectivefadingillustrationTimeandfrequencyresponseofafrequencyselectivefadingchannel,2.3Channelcorrelationfunctions,BasicType2.Frequency-SelectiveFading,Fastfading（timeselectivefading）ChannelimpulseresponsechangesrapidlywithineachsymboldurationRequirement:

@#@DopplerspreadcausesfrequencydispersionsignaldistortionOccursusuallyforverylowdatarate,thechangeofchanneliscausedbymotion,2.3Channelcorrelationfunctions,BasicType3.FastFading,SlowfadingChannelisstaticoversomesymbolintervalsRequirements:

@#@ChannelimpulseresponsechangesslowerthansymbolsDopplerspreadismuchlessthanbasebandsignalbandwidthDeterminedbythemobilevelocityandsignal,2.3Channelcorrelationfunctions,BasicType4:

@#@SlowFading,Fadingtypesexperiencedbyasignaldependonthesignalssymbolrateorbandwidth,SymbolintervalTs,SymbolintervalTs,Tc,BasebandsignalbandwidthBs,Bd,Bc,BasebandsignalbandwidthBs,Ts,Bs,Ts,Bs,Ts,2.3Channelcorrelationfunctions,FourCompositeFadings,Example2.14,ConsiderafadingchannelwhichexhibitsaDopplerfrequencyshiftuniformlydistributedbetween-10Hzand10Hz.DetermineThemeanDopplershiftTheRMSDopplerspread,andThecoherencetime,2.3Channelcorrelationfunctions,4、Examples,Example2.15,ConsideraWSSUSchannelwhosetime-variantimpulseresponseisgivenbyWhereTandareconstant,isarandomvariableuniformlydistributedin,andisareal-valuedrandomprocessindependentof,withandCalculatethedelaypsdandthemultipathdelayspreadCalculatethefrequencycorrelationfunctionandthechannelcoherencebandwidthDeterminewhetherthechannelexhibitsfrequency-selectivefadingforGSMsystemswithT=0.1ms,2.3Channelcorrelationfunctions,Example2.15,ForthechannelspecifiedinExample2.14with,findTheDopplerPSDThemeanDopplershiftandtheRMSDopplerspreadThechannelcoherencetime,andWhetherthechannelexhibitsslowfadingforGSMsystems,2.3Channelcorrelationfunctions,2.3Channelcorrelationfunctions,2.3.2FrequencyandTimeCorrelationFunction,2.3.4Examples,2.3.1DelayPowerSpectralDensity,2.3.3DopplerPowerSpectralDensity,Conclusions,Prob