无线电通信原理-第三章(英文)

2024/12/221MobileRadioPropagation:

Large-ScalePathLoss2024/12/222Small-scaleandlarge-scalefading

2024/12/223ThethreeBasicPropagationMechanismReflection:occurfromthesurfaceoftheearthandfrombuildingsandwalls.Diffraction:occurswhentheradiopathbetweenthetransmitterandreceiverisobstructedbyasurfacethathassharpirregularities(edges).

Scattering:occurswhenthemediumthroughwhichthewavetravelsconsistsofobjectswithdimensionsthataresmallcomparedtothewavelength,andwherethenumberofobstaclesperunitvolumeislarge.2024/12/224SpectrumVLF=VeryLowFrequency,LF=LowFrequency,MF=MediumFrequency,HF=HighFrequency,VHF=VeryHighFrequency,UHF=UltraHighFrequency,SHF=SuperHighFrequency,EHF=ExtraHighFrequency,UV=UltravioletLight,Frequencyandwavelength:

=c/f,wavelength

,speedoflightc3x108m/s,frequencyf1Mm300Hz10km30kHz100m3MHz1m300MHz10mm30GHz100m3THz1m300THzvisiblelightVLFLFMFHFVHFUHFSHFEHFinfraredUVopticaltransmissioncoaxcabletwistedpair2024/12/225FrequenciesformobilecommunicationVHF-/UHF-rangesformobileradiosimple,smallantennaforcarsdeterministicpropagationcharacteristics,reliableconnectionsSHFandhigherfordirectedradiolinks,satellitecommunicationsmallantenna,focusinglargebandwidthavailableWirelessLANsusefrequenciesinUHFtoSHFspectrum2024/12/226FreeSpacePropagationModelInfreespace,thereceivedpowerispredictedbyPr(d):ReceivedpowerwithadistancedbetweenTxandRxPt:TransmittedpowerGt:TransmittingantennagainGr:Receiveantennagain:Thewavelengthinmeters.d:distanceinmetersL:ThemiscellaneouslossesL(L>=1)areusuallyduetotransmissionlineattenuation,filterlosses,andantennalossesinthecommunicationsystem.L=1indicatesnolossinthesystemhardware.2024/12/227EIRP&ERPEIRP:EffectiveIsotropicRadiatedPowerRepresentsthemaximumradiatedpoweravailablefromatransmitterinthedirectionofmaximumantennagain,ascomparedtoanisotropicradiator.ERP:EffectiveRadiatedPowerERPisusedinsteadofEIRPtodenotethemaximumradiatedpowerascomparedtoahalf-wavedipoleantenna(insteadofanisotropicantenna).Inpractice,antennagainsaregiveninunitsofdBi(dBgainwithrespecttoanisotropicsourse)ordBd(dBgainwithrespecttoahalf-wavedipole)2.15dB2024/12/2289dBiantenna&3dBiantenna2024/12/229PathLossThepathloss,whichrepresentssignalattenuationasapositivedifference(indB)betweentheeffectivetransmittedpowerandthereceivedpower.ThepathlossforthefreespacemodelwhenantennagainsareincludedisgivenbyquantitymeasuredindB,isdefinedastheWhenantennagainsareexcluded,theantennasareassumedtohaveunitygain,andpathlossisgivenby(f:MHz,d:km)2024/12/2210Thefar-fieldregionofatransmittingantennaTheFriisfreespacemodelisonlyavalidpredictorforPrforvaluesofd,whichareinthefar-fieldofthetransmittingantenna.Thefar-fieldofatransmittingantennaisdefinedastheregionbeyondthefar-fielddistancedf

,whichisrelatedtothelargestlineardimensionofthetransmitterantennaapertureandthecarrierwavelength.Thefar-fielddistanceisgivenbyTobeinthefar-fieldregion,dmustsatisfy2024/12/2211TheReferenceDistanceItisclearthatequationdoesnotholdford=0.Forthisreason,large-scalepropagationmodelsuseaknownreceivedpowerreferencepoint.Thereceivedpower,Pr(d),atanydistanced>d0,mayberelatedtoPratd0.IfPrisinunitsofdBmordBW,thereceivedpowerisgivenby2024/12/2212Log-distancepathlossmodelBoththeoreticalandmeasurement-basedpropagationmodelsindicatethataveragereceivedsignalpowerdecreaseslogarithmicallywithdistance,whetherinoutdoororindoorchannels.Theaveragelarge-scalepathlossforanarbitraryT-Rseparationisexpressedasafunctionofdistancebyusingpathlossexponentn.nisthepathlossexponentwhichindicatestherateatwhichthepathlossincreaseswithdistanced0istheclose-inreferencedistancewhichisdetermineddistheT-Rseparationdistance2024/12/2213Ifatransmitterproducespower:Pt=50w,receivesensitivity(minimumusablesignallevel)is-100dbm.Assumed0=100m,witha900MHzcarrierfrequency,n=4,Gt=Gr=1;findthecoveragedistanced.TransmitPower:Pt=50W=47dBmPr(d0)=-24.5dBmPL(dB)=40log(d/d0)=-24.5-(-100)=75.5dbmIfn=4,log(d/d0)=75.5/40=1.8875,d=7718mExample12024/12/22142024/12/2215Log-normalShadowingThemodelinEquation(3.11)doesnotconsiderthefactthatthesurroundingenvironmentalcluttermaybevastlydifferentattwodifferentlocationshavingthesameT-Rseparation.ThisleadstomeasuredsignalswhicharevastlydifferentthantheaveragevaluepredictedbyEquation(3.11).

2024/12/2216SimulationResultsDeepshadowingSlightShadowing2024/12/2217Log-normalShadowing

2024/12/2218DeterminationofPercentageofCoverageArea2024/12/2219asafunctionofprobabilityofsignalabovethresholdonthecellboundary.2024/12/2220Fourreceivedpowermeasurementsweretakenatdistancesof100m,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).

Example22024/12/2221ThevalueofnwhichminimizesthemeansquareerrorcanbeobtainedbyequatingthederivativeofJ(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=4.4.2024/12/2222(b)Thesamplevariance

2=J(n)/4atn=4.4canbeobtainedasfollows.

therefore=6.17dB,whichisabiasedestimate.2024/12/2223(c)Theestimateofthereceivedpoweratd=2kmis(d)Theprobabilitythatthereceivedsignallevelwillbegreaterthan-60dBmis(e)67.4%oftheusersontheboundaryreceivesignalsgreaterthan-60dBm,then92%ofthecellareareceivescoverageabove–60dbm2024/12/2224OutdoorPropagationModelsOkumuraModel(150-1920MHz,1km-100km)HataModel(150-1500MHz,1km-20km)EgliModel(40-400MHz,0-64km)2024/12/2225

OkumuraModel

notprovideanyanalyticalexplanation

itsslowresponsetorapidchangesinterrain

2024/12/2226Okumuramedianattenuationandcorrection2024/12/2227FindthemedianpathlossusingOkumura'smodelford=50km,hte

=100m,hre

=10minasuburbanenvironment.IfthebasestationtransmitterradiatesanEIRPof1kWatacarrierfrequencyof900MHz,findthepoweratthereceiver(assumeaunitygainreceivingantenna).

Example32024/12/2228HATAmodel&COST–231extension2024/12/2229Example4Inthesuburbanofalargecity,d=10km,hte

=200m,hre

=2m,carrierfrequencyof900MHz,usingHATA’smodelfindthepathloss.

2024/12/2230Indoorpropagationmodels2024/12/2231FeatureofIndoorRadioChannelThedistancescoveredaremuchsmaller,andthevariabilityoftheenvironmentismuchgreaterforamuchsmallerrangeofT-Rseparationdistances.Ithasbeenobservedthatpropagationwithinbuildingsisstronglyinfluencedbyspecificfeaturessuchasthelayoutofthebuilding,theconstructionmaterials,andthebuildingtype.Indoorradiopropagationisdominatedbythesamemechanismsasoutdoor:reflection,diffraction,andscattering.However,conditionsaremuchmorevariable.

2024/12/2232PathattenuationfactorsPartitionLossesinthesamefloorPartitionLossesbetweenFloors(floorattenuationfactors,FAF)2024/12/2233Log-distancePathLossModelIndoorpathlosshasbeenshownbymanyresearcherstoobeythedistancepowerlaw

Wherethevalueofndependsonthesurroundingsandbuildingtype,andXrepresentsanormalrandomvariableindBhavingastandarddeviationofsigma.Thisisidenticalinformtothelog-normalshadowingmodelofoutdoorpathattenuationmodel.2024/12/2234AttenuationFactorModelWherenSF

representstheexponentvalueforthe“samefloor”measurement.ThepathlossonadifferentfloorcanbepredictedbyaddinganappropriatevalueofFAF2024/12/2235SignalPenetrationintobuildingsRFpenetrationhasbeenfoundtobeafunctionoffrequencyaswellasheightwithinthebuildingMeasurementsshowedthatpenetrationlossdecreaseswithincreasingfrequency.Specifically,penetrationattenuationvaluesof16.4dB,11.6dB,and7.6dBweremeasuredonthegroundfloorofabuildingatfrequenciesof441MHz,896.5MHz,and1400Mhz,respectly.Resultsshowedthatbuildingpenetrationlossdecreasedatarateof1.9dBperfloorfromthegroundleveluptothefifteenthfloorandthenbeganincreasingabovethefifteenfloor.2024/12/2236RayTracingandSiteSpecificModeling

Inrecentyears,thecomputationalandvisualizationcapabilitiesofc