wireless communications - chapter 5 - mobile radio propagation(05-10)

《wireless communications - chapter 5 - mobile radio propagation(05-10)》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

1、Chapter5.MobileRadioPropagationSmall-ScalefadingandmultiPath¢Small-ScaleMultipath°ImpulseResponseModelofaMultipathCh.°Small-ScaleMultipathMeasurements°ParametersofMobileMultipathChannel°TypesofSmall-ScaleFading°RayleighandRiceanDistributions°StatisticalModelsforMultipat

2、hFadingCh.5.1Small-ScaleMultipathPropagation°Small-scalefading,orsimplyfading,isusedtodescribetherapidfluctuationsoftheamplitudes,phases,ormultipathdelaysofaradiosignaloverashortperiodoftimeortraveldistance,sothatlarge-scalepathlosseffectsmaybeignored.°Fadingiscausedbyi

3、nterferencebetweentwoormoreversionsofthetransmittedsignalwhicharriveatthereceiveratslightlydifferenttimes.°Multipathintheradiochannelcreatessmall-scalefadingeffects.°Mostimportanteffects：（1）Rapidchangesinsignalstrengthoverasmalltraveldistanceortimeinterval;（2）Randomfreq

4、uencymodulationduetovaryingDopplershiftsondifferentmultipathsignals;（3）Timedispersion(echoes)causedbymultipathpropagationdelays.¢FactorsInfluencingSmall-ScaleFading：（1）Multipathpropagation－signalsmearingduetoISI.（2)Speedofthemobile－randomfrequencymodulationduetodifferen

5、tDopplershiftsoneachofthemultipathcomponents.（3）Speedofsurroundingobjects－timevaryingDopplershiftonmultipathcomponents.（4）Thetransmissionbandwidthofthesignal－transmittedradiosignalbandwidthisgreaterthanthe“bandwidth”ofthemultipathchannel,thereceivedsignalwillbedistorted

6、.°DopplerShift22π∆lvπ∆t由路程差造成的接收信号相位变化为：∆=ϕ＝cosθλλ1∆ϕv频率变化，即多普勒频移ff为：=⋅=⋅cosθdd2πλ∆tS∆lθθXdYv5.2ImpulseResponseModelofaMultipathCh..°Thesmall-scalevariationscandirectlyrelatedtotheimpulseresponseofmobilech.;°Theimpulseresponseisawidebandchannelcharacterizationandcontain

7、sallinformationnecessarytosimulateoranalyzeanytypeofradiotransmissionthroughthechannel;°Amobilechannelmaybemodeledasalinearfilterwithatimevaryingimpulseresponse.°ImpulseResponseModelofaMultipathChannelxt()hthtejωctyt()ct()1(,)rt()(,ττ)=Re{b(,)}2htbτ带通信道的冲击响应模型基带的等效信道冲击响

8、应模型1y(t)=⊗xt()h(t)r(t)=ct()⊗h(t)b2xt()==Re{}ct()exp()j2ππfccty(t)Re{}r(t)exp()j2ftL−1htbl(,τα)=+∑(t,τ)exp⎡⎤⎣⎦j