无线通信原理与应用第三章.ppt

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1、Chapter3:MobileRadioPropagation:Large-ScalePathLoss7/28/202113.1IntroductiontoRadiowavePropagationSmall-scaleandlarge-scalefading7/28/202123.2FreeSpacePropagationModelInfreespace,thereceivedpowerispredictedbyFiriisEqu.Pr(d):Receivedpowerwithadistancedbe

2、tweenTxandRxPt:TransmittedpowerGt:TransmittingantennagainGr:Receiveantennagain:Thewavelengthinmeters.d:distanceinmetersL:ThemiscellaneouslossesL(L>=1)areusuallyduetotransmissionlineattenuation,filterlosses,andantennalossesinthecommunicationsystem.L=1indi

3、catesnolossinthesystemhardware.7/28/20213Reflection:occurfromthesurfaceoftheearthandfrombuildingsandwalls.Diffraction:occurswhentheradiopathbetweenthetransmitterandreceiverisobstructedbyasurfacethathassharpirregularities(edges).Scattering:occurswhentheme

4、diumthroughwhichthewavetravelsconsistsofobjectswithdimensionsthataresmallcomparedtothewavelength,andwherethenumberofobstaclesperunitvolumeislarge.3.3ThethreeBasicPropagationMechanisms7/28/20214reflection（反射）atlargeobstacles,Scattering(散射)atsmallobstacles

5、,diffraction(衍射)atedges7/28/20215EIRP&ERPEIRP:EffectiveIsotropicRadiatedPowerRepresentsthemaximumradiatedpoweravailablefromatransmitterinthedirectionofmaximumantennagain,ascomparedtoanisotropicradiator.ERP:EffectiveRadiatedPowerERPisusedinsteadofEIRPtode

6、notethemaximumradiatedpowerascomparedtoahalf-wavedipoleantenna(insteadofanisotropicantenna).Inpractice,antennagainsaregiveninunitsofdBi(dBgainwithrespecttoanisotropicsourse)ordBd(dBgainwithrespecttoahalf-wavedipole)2.15dB7/28/202169dBiantenna&3dBiantenna

7、7/28/20217PathLossThepathloss,whichrepresentssignalattenuationasapositivedifference(indB)betweentheeffectivetransmittedpowerandthereceivedpower.ThepathlossforthefreespacemodelwhenantennagainsareincludedisgivenbyquantitymeasuredindB,isdefinedastheWhenante

8、nnagainsareexcluded,theantennasareassumedtohaveunitygain,andpathlossisgivenby(f:MHz,d:km)7/28/20218TheFriisfreespacemodelisonlyavalidpredictorforPrforvaluesofd,whichareinthefar-fieldofthetransmittingantenna.Thefar-fieldofa