无线通信原理课件 第四章.ppt

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1、2021/7/281MobileRadioPropagation:Small-ScaleFadingandMultipathChapter 42021/7/282ContentsofChapter 41.Small-ScaleMultipathPropagation2.ImpulseresponseModelofMultipathchannels3.ParametersofMobileMultipathChannels4.TypesofSmall-ScaleFading5.RayleighandRic

2、eanDistributions2021/7/283Chapter 41.Small-ScaleMultipathPropagation2.ImpulseresponseModelofMultipathchannels3.ParametersofMobileMultipathChannels4.TypesofSmall-ScaleFading5.RayleighandRiceanDistributions2021/7/2842021/7/285Fading(small-scale)isamorerap

3、idfluctuationofsignals–causedby•Multipatheffect,constructiveanddestructiveinterferencebetweentwoormoreversionsofthesamesignal•Dopplereffect,duetomovingterminalsorsurroundingsSmall-Scalefading2021/7/286Multipath2021/7/287Time-variantmultipathchannel2021/

4、7/288Multipath2021/7/289DopplerShiftfre:receivedfrequencyfc:carrierfrequencyfd:dopplershift2021/7/2810DopplerShift“A”“B”2021/7/2811DopplerShift2021/7/2812DopplerShiftExampleCarrierfrequencyfc=1850MHz(i.e.=16.2cm)Vehiclespeedv=60mph=26.82m/sIfthevehicle

5、ismovingdirectlytowardsthetransmitterIfthevehicleismovingperpendiculartotheangleofarrivalofthetransmittedsignal(PP.180)2021/7/2813CoherenceBandwidth&CoherenceTime2021/7/2814CharacteristicsofRadioChannel(Largepathloss)Multipath(reflection,scattering)Time

6、-variant(time-varying,aconsequenceoftheconstantlychangingphysicalcharacteristicsofthemedia,e.g.movingofobjects)Itisreasonabletocharacterizethetime-variantmultipathchannelsstatistically.Timespread(multipath)Frequencyspread(time-variant)2021/7/2815Chapter

7、 41.Small-ScaleMultipathPropagation2.ImpulseresponseModelofMultipathchannels3.ParametersofMobileMultipathChannels4.TypesofSmall-ScaleFading5.RayleighandRiceanDistributions2021/7/2816ImpulseresponseofwirelesschannelsThemobilechannelcanbemodeledasalinear,

8、timevaryingfilterwithimpulseresponseh(t,t),wheretisthechannelmultipathdelayforafixedt.Theimpulseresponseh(t,t)completelycharacterizesthechannelandisafunctionofbothtandtThereceivedsignalcanbeexpressedasaconvolutionofthechannelimpu