无线通信原理与应用第三章

14.06.2020,.,1,Chapter3:MobileRadioPropagation:Large-ScalePathLoss,14.06.2020,.,2,3.1IntroductiontoRadiowavePropagationSmall-scaleandlarge-scalefading,14.06.2020,.,3,3.2FreeSpacePropagationModel,Infreespace,thereceivedpowerispredictedbyFiriisEqu.,Pr(d):ReceivedpowerwithadistancedbetweenTxandRxPt:TransmittedpowerGt:TransmittingantennagainGr:Receiveantennagain:Thewavelengthinmeters.d:distanceinmetersL:ThemiscellaneouslossesL(L=1)areusuallyduetotransmissionlineattenuation,filterlosses,andantennalossesinthecommunicationsystem.L=1indicatesnolossinthesystemhardware.,14.06.2020,.,4,Reflection:occurfromthesurfaceoftheearthandfrombuildingsandwalls.Diffraction:occurswhentheradiopathbetweenthetransmitterandreceiverisobstructedbyasurfacethathassharpirregularities(edges).Scattering:occurswhenthemediumthroughwhichthewavetravelsconsistsofobjectswithdimensionsthataresmallcomparedtothewavelength,andwherethenumberofobstaclesperunitvolumeislarge.,3.3ThethreeBasicPropagationMechanisms,14.06.2020,.,5,reflection（反射）atlargeobstacles,Scattering(散射)atsmallobstacles,diffraction(衍射)atedges,14.06.2020,.,6,EIRPfindthecoveragedistanced.TransmitPower:Pt=50W=47dBmPr(d0)=-24.5dBmPL(dB)=40log(d/d0)=-24.5-(-100)=75.5dbIfn=4,log(d/d0)=75.5/40=1.8875,d=7718m,Example1,14.06.2020,.,14,ThemodelinEquation(3.11)doesnotconsiderthefactthatthesurroundingenvironmentalcluttermaybevastlydifferentattwodifferentlocationshavingthesameT-Rseparation.ThisleadstomeasuredsignalswhicharevastlydifferentthantheaveragevaluepredictedbyEquation(3.11).,Log-normalShadowing,14.06.2020,.,15,Log-normalShadowing,14.06.2020,.,16,DeterminationofPercentageofCoverageArea,14.06.2020,.,17,U(r)asafunctionofprobabilityofsignalabovethresholdonthecellboundary.,14.06.2020,.,18,Example2,Alocalaveragesignalstrengthfieldmeasurements,themeasureddatafitadistant-dependentmeanpowerlawmodelhavingalog-normaldistributionaboutthemean.Assumethemeanpowerlawwasfoundtobe.Ifasignalof1mWwasreceivedatd0=1mfromthetransmitter,andatadistanceof10m,10%ofthemeasurementswerestrongerthan-25dBm,definethestandarddeviation,forthepathlossmodelatd=10m.,14.06.2020,.,19,Fourreceivedpowermeasurementsweretakenatdistancesof100m,200m,1km,and3kmfromatransmitter.Thesemeasuredvaluesaregiveninthefollowingtable.ItisassumedthatthepathlossforthesemeasurementsfollowsthemodelinEquation(3.12.a),whered0=100m:(a)findtheminimummeansquareerror(MMSE)estimateforthepathlossexponent,n;(b)calculatethestandarddeviationaboutthemeanvalue;(c)estimatethereceivedpoweratd=2kmusingtheresultingmodel;(d)predictthelikelihoodthatthereceivedsignallevelat2kmwillbegreaterthan-60dBm;and(e)predictthepercentageofareawithina2kmradiuscellthatreceivessignalsgreaterthan-60dBm,giventheresultin(d).,Example3,14.06.2020,.,20,ThevalueofnwhichminimizesthemeansquareerrorcanbeobtainedbyequatingthederivativeofJ(n)tozero,andthensolvingforn.(a)UsingEquation(3.11),wefind=pi(d0)-10nlog(di/100m).RecognizingthatP(d0)=0dBm,wefindthefollowingestimatesforp,indBm:,TheMMSEestimatemaybefoundusingthefollowingmethod.Letpibethereceivedpoweratadistancedi,andletbetheestimateforpiusingthepathlossmodelofEquation(3.10).Thesumofsquarederrorsbetweenthemeasuredandestimatedvaluesisgivenby,Settingthisequaltozero,thevalueofnisobtainedasn=4.4.,14.06.2020,.,21,(b)Thesamplevariance2=J(n)/4atn=4.4canbeobtainedasfollows.,therefore=6.17dB,whichisabiasedestimate.,14.06.2020,.,22,(c)Theestimateofthereceivedpoweratd=2kmis(d)Theprobabilitythatthereceivedsignallevelwillbegreaterthan-60dBmis(e)67.4%oftheusersontheboundaryreceivesignalsgreaterthan-60dBm,then92%ofthecellareareceivescoverageabove60dbm,14.06.2020,.,23,3.5OutdoorPropagationModels,OkumuraModel(150-1920MHz,1km-100km)HataModel(150-1500MHz,1km-20km)EgliModel(40-400MHz,0-64km),14.06.2020,.,24,notprovideanyanalyticalexplanationitsslowresponsetorapidchangesinterrain,OkumuraModel,14.06.2020,.,25,Okumuramedianattenuationandcorrection,14.06.2020,.,26,FindthemedianpathlossusingOkumurasmodelford=50km,hte=100m,hre=10minasuburbanenvironment.IfthebasestationtransmitterradiatesanEIRPof1kWatacarrierfrequencyof900MHz,findthepoweratthereceiver(assumeaunitygainreceivingantenna).,Example4,14.06.2020,.,27,HATAmodel&COST231extension,14.06.2020,.,28,Example5,Inthesuburbanofalargecity,d=10km,hte=200m,hre=2m,carrierfrequencyof900MHz,usingHATAsmodelfindthepathloss.,14.06.2020,.,29,3.6Indoorpropagationmodels,14.06.2020,.,30,FeatureofIndoorRadioChannel,Thedistancescoveredaremuchsmaller,andthevariabilityoftheenvironmentismuchgreaterforamuchsmallerrangeofT-Rseparationdistances.Ithasbeenobservedthatpropagationwithinbuildingsisstronglyinfluencedbyspecificfeaturessuchasthelayoutofthebuilding,theconstructionmaterials,andthebuildingtype.Indoorradiopropagationisdominatedbythesamemechanismsasoutdoor:reflection,diffraction,andscattering.However,conditionsaremuchmorevariable.,14.06.2020,.,31,Pathattenuationfactors,PartitionLossesinthesamefloorPartitionLossesbetweenFloors(floorattenuationfactors,FAF),14.06.2020,.,32,Log-distancePathLossModel,IndoorpathlosshasbeenshownbymanyresearcherstoobeythedistancepowerlawWherethevalueofndependsonthesurroundingsandbuildingtype,andXrepresentsanormalrandomvariableindBhavingastandarddeviationofsigma.Thisisidenticalinformtothelog-normalshadowingmodelofoutdoorpathattenuationmodel.,14.06.2020,.,33,AttenuationFactorModel,WherenSFrepresentstheexponentvalueforthe“samefloor”measurement.ThepathlossonadifferentfloorcanbepredictedbyaddinganappropriatevalueofFAF,14.06.2020,.,34,SignalPenetrationintobuildings,RFpenetrationhasbeenfoundtobeafunctionoffrequencyaswellasheightwithinthebuildingMeasurementsshowedthatpenetrationlossdecreaseswithincreasingfrequency.Specifically,penetrationattenuationvaluesof16.4dB,11.6dB,and7.6dBweremeasuredonthegroundfloorofabuildingatfrequenciesof441MHz,896.5MHz,and1400Mhz,respectly.Resultsshowedthatbuildingpenetrationlossdecreasedatarateof1.9dBperfloorfromthegroundleveluptothefifteenthfloorandthenbeganincreasingabovethefifteenfloor.,14.06.2020,.,35,RayTracingandSiteSpecificModeling,Inrecentyears,thecomputationalandvisualizationcapabilitiesofcomputershaveacceleratedrapidly.NewmethodsforpredictingradiosignalcoverageinvolvetheuseofSiteSpecific(SISP)propagationmodelsandgraphicalinformationsystem(GIS)database.SISPmodelssupportraytracingasameansofdeterministicallymodelinganyindoororoutdoorpropagationenvironment.Throughtheuseofbuildingdatabases,whichmaybedrawnordigitizedusingstandardgraphicalsoftw