2023学年完整公开课版Fastfadingandslowfading

FastfadingandslowfadingMobileCommunicationTechnologyLecturer：GuYanhua01020304ClassificationofChannelFadingFastFadingSlowFadingCalculateoftheFadingCONTENT01ClassificationofFadingChannelPARTONEMobilephoneBasestationElectromagneticwaveWirelesschannelWireless+User'smobilityThereceivedfieldstrengthfluctuatesrapidlyThefadingofthesynthesizedsignalatthereceivingendClassificationofChannelFadinglossofthemobilechannelLossofpathpropagationLossoffadingFastfading（causedbymultipatheffect）Slowfading（causedbyshadoweffect）referstothelosscausedbytheenergyemissionofelectromagneticwaveinspace.ClassificationofChannelFadingIdealpointsourceantennaE’EItisassumedthatthereexistsanidealpointsourceantennainfreespace:Sphericalwaveformedbypointsourceradiation;TheenergyfieldofanypointontheinnersphereissetasE;TheenergyfieldatanypointontheoutersphereissetasE';Infreespace,thesumofenergyofinnersphereisequaltothesumofenergyofoutersphere,andtheareaofinnersphereislessthanthatofoutersphere;Therefore,theenergyvalueatpointE>pointEAlongthedirectionoftheray,itcanbeseenthatthefieldstrengthmeasuredalongtheidealpointsourcewillgraduallyweaken.ClassificationofChannelFading02FastFadingPARTTWODefinitionStatisticalcharacteristicsReasonmultipatheffectFastfadingiscausedbymultipatheffect.Thefadingrate(halfofthetimesofsignalenvelopepassingthroughthemedianlevelpersecond)canreach30-40timespersecond,andthefadingdepth(signalvariationrange)isabout30dB.Suchfadingiscalledfastfading,multipathfading,transientfadingorsmall-scalefading.RiciandistributionorRayleighdistribution.FastFadingthepropagationmodeloftheelectromagneticwaveResearchcontentthechangetrendoftheaverageleveloftheactualreceivedsignalResearchmethodsFastFading12FastFadinginamultipathpropagationchannel,therearenchannelsignals,whichareindependentofeachother,andthereisnodominantsignal.Thereareonlymanyreflectedwavesignals,andthefadingchangeofreceivedsignalenvelopefollowsRayleighdistribution.therearenchannelsignalsinthemultipathpropagationchannel,whichareindependentofeachother.Whenthereceivedsignalsincludestrongdirectwavesignalsanditdominates,thefadingofthereceivedsignalenvelopeobeystheRiciandistribution.03SlowFadingPARTTWOthemedianfieldstrengthatthereceivingantennafluctuateswiththechangesofsurroundingterrainandbuildingswhenthemobilestationismoving,anditschangerateisrelativelyslow.DefinitionReasonShadoweffectStatisticalcharacteristicsnormaldistributionSlowFading04CalculateoftheFadingPARTFOURFreespacepropagationmodel

Freespacepropagationmodel，Itreferstotheradiowavepropagationwhenthereisaninfinitevacuumaroundtheantenna,whichisanidealpropagationcondition.Whenradiowavepropagatesinfreespace,itsenergywillnotbeabsorbedbyobstacles,norwillitreflectorscatter.。CalculateoftheFading

thedefinitionoffreespacepropagationloss(

Lbs):

IndB，Or

［Lbs］(dB)=32.45+20lgd(km)+20lgf(MHz)wheretheunitofdisKm,theunitoffisMHz.MajorpointCalculateoftheFadingQuestions：（1）Iftheelectromagneticwavepropagatesinfreespace,theworkingfrequencyis1800MHz,andthepropagationdistanceis10km,whatdBisthepropagationloss??

answer：Lbs=32.45+20lg10+20lg1800=117.55(dB)（2）Ifthesamepropagationenvironment,theworkingfrequencyfandthepropagationdistancedbecometwotimesoftheoriginal,thenhowdoesthepropagationlosschange?？

answer：Lbs2-Lbs1=20lg2f+20lg2d-20lgf-20lgd=20lg2+20lg2=12(dB)CalculateoftheFadingThelosscausedbyfadingthelossofsignalfadingcausedbymultipatheffectandshadoweffectisaffectedbymobilechannel,whichisacompletelyrandomprocess,anditisdifficulttocalculatetheaccuratelossvalue.themethodincommunicationengineering

Onthebasisofalargenumberoffieldstrengthtests,themethodincommunicationengineeringistofindouttherelationshipbetweenpropagationlossanddistance,frequencyandantennaheightundervariousterrainandgroundfeatures,givevariouschartsandcalculationformulasofpropagationcharacteristics,andestablishpropagationpredictionmodel,soastopredictthemedianvalueofreceivedsignalwithasimplermethod.CalculateoftheFadingCommonmodelsofpropagationprediction:Okumura/HatamodelCOST231-HatamodelCOST231Walfish-IkegamimodelKeenan-MotleymodelComputeraidedcalculationmodelCalculateoftheFadingDiscriminationofcommonunits(Supplement)ThereasonusedBm\dB:

indailyuse,powerisusuallyexpressedinW,MWandotherunits,butitisnotconvenientinpracticalwork,sodBm,dBandotherunitsareintroduced.DefinitionofdBm:

WhenthetransmissionpowerPis1mW,itisconvertedintodBmandthenconvertedto0dbm.CalculationformulaofdBm:

10*log（P/1mw）

typicalvalues：

1w=30dBm5w=37dBm2w=33dBm10w=40dBm

Discriminationofcommonunits(Supplement)DefinitionofdB：

dBisavaluerepresentingtherelativevalue.