Multipath and Doppler Effects and Models

《Multipath and Doppler Effects and Models》由会员上传分享，免费在线阅读，更多相关内容在学术论文-天天文库。

1、MultipathandDopplerEffectsandModelsTherearetwopartsinthislecture.•InPartI,wewillfirstintroducethemutipathpropagationeffectsandDopplerfrequencyshift/spreadeffects.•InPartII,wewillbrieflyintroducemultipathandDopplerchannelmodels.1Background:OverviewsonWirelessChannelModelingWeneedtoaskthef

2、ollowingthreeimportantquestionswhiledesigningawirelesscommunicationlink:1.Fading&PowerLoss:Isthesignaltointerferenceplusnoiseratio(SINR)largeenoughforthereceivertodetectthetransmittedsignal?2.SignalDistortion:Canthesignaldistortionbeignored,predictedorremovedsothatweknowhowtorecoverthetr

3、ansmittedinformationatthereceiver?3.TimeVariation:Canthereceiveradaptfasterenoughtothevariationsoftheabovetwofeatures(SINR&signaldistortion)?AcompletewirelesschannelmodelshouldprovidequantitativemeasuresofSINR,signaldistortionandtimevariation.ForSINR(referredinquestion1),weneedonlytocons

4、iderthetimeinvarianttransmissionlossatasinglefrequency(thatistheRFcarrierfrequency).Thefrequencyandtimedependentpropertiesofsignalcanbeaddressedinansweringquestions2and3.Signaldistortion(referredinquestion2)iscausedbythefrequencydependentvariationsofthereceivedsignalstrengthandphase.Thep

5、rimarysourceoffrequencydependentvariationsismultipathpropagation.Here,weneedonlytoconsidertimeinvariantsituationsandleavethetimevaryingfeaturestoquestion3.Motionsofreceivers,transmittersorwirelessenvironmentsgenerateDopplereffects.WithDopplereffects,signalfrequenciesshiftandspread.TheseD

6、opplereffectswillcausetimevariationsinthereceivedsignalstrengthandwaveshape.Thiskindoftimevaryingfeaturesisusuallyrandomandcanbemodeledasstochasticprocesses.Inordertoaddressingthesethreeimportantissues,wedividewirelesschannelmodelingintothreeparts:•Transmissionloss-singlefrequency(ornarr

7、owbandsignal)-timeinvariantenvironment(orshortobservationtimeperiod)•Frequencydependentchannelimpulseresponseortransferfunction-multiplefrequencies(orbroadbandsignal)-timeinvariantenvironment(orshortobservationtimeperiod)•Timevaryingchannelimpulseresponseortransferfunctio