無線通信網(wǎng)絡(luò)天線與傳播

無線通信網(wǎng)絡(luò)天線與傳播第1頁，課件共36頁，創(chuàng)作于2023年2月IntroductionAnantennaisanelectricalconductororsystemofconductorsTransmission-radiateselectromagneticenergyintospaceReception-collectselectromagneticenergyfromspaceIntwo-waycommunication,thesameantennacanbeusedfortransmissionandreception第2頁，課件共36頁，創(chuàng)作于2023年2月RadiationPatternsRadiationpatternGraphicalrepresentationofradiationpropertiesofanantennaDepictedastwo-dimensionalcrosssectionBeamwidth(orhalf-powerbeamwidth)

MeasureofdirectivityofantennaReceptionpatternReceivingantenna’sequivalenttoradiationpattern第3頁，課件共36頁，創(chuàng)作于2023年2月TypesofAntennasIsotropicantenna(idealized)RadiatespowerequallyinalldirectionsDipoleantennasHalf-wavedipoleantenna(orHertzantenna)Quarter-waveverticalantenna(orMarconiantenna)ParabolicReflectiveAntenna第4頁，課件共36頁，創(chuàng)作于2023年2月AntennaGain AntennagainPoweroutput,inaparticulardirection,comparedtothatproducedinanydirectionbyaperfectomnidirectionalantenna(isotropicantenna)EffectiveareaRelatedtophysicalsizeandshapeofantenna第5頁，課件共36頁，創(chuàng)作于2023年2月AntennaGainRelationshipbetweenantennagainandeffectiveareaG=antennagainAe

=effectiveareaf=carrierfrequencyc=speedoflight(?3′108m/s)=carrierwavelength第6頁，課件共36頁，創(chuàng)作于2023年2月PropagationModesGround-wavepropagationSky-wavepropagationLine-of-sightpropagation第7頁，課件共36頁，創(chuàng)作于2023年2月GroundWavePropagation第8頁，課件共36頁，創(chuàng)作于2023年2月GroundWavePropagationFollowscontouroftheearthCanPropagateconsiderabledistancesFrequenciesupto2MHzExampleAMradio第9頁，課件共36頁，創(chuàng)作于2023年2月SkyWavePropagation第10頁，課件共36頁，創(chuàng)作于2023年2月SkyWavePropagationSignalreflectedfromionizedlayerofatmospherebackdowntoearthSignalcantravelanumberofhops,backandforthbetweenionosphereandearth’ssurfaceReflectioneffectcausedbyrefractionExamplesAmateurradioCBradio第11頁，課件共36頁，創(chuàng)作于2023年2月Line-of-SightPropagation第12頁，課件共36頁，創(chuàng)作于2023年2月Line-of-SightPropagationTransmittingandreceivingantennasmustbewithinlineofsightSatellitecommunication–signalabove30MHznotreflectedbyionosphereGroundcommunication–antennaswithineffectivelineofsiteduetorefractionRefraction–bendingofmicrowavesbytheatmosphereVelocityofelectromagneticwaveisafunctionofthedensityofthemediumWhenwavechangesmedium,speedchangesWavebendsattheboundarybetweenmediums第13頁，課件共36頁，創(chuàng)作于2023年2月Line-of-SightEquationsOpticallineofsightEffective,orradio,lineofsightd=distancebetweenantennaandhorizon(km)h=antennaheight(m)K=adjustmentfactortoaccountforrefraction,ruleofthumbK=4/3第14頁，課件共36頁，創(chuàng)作于2023年2月Line-of-SightEquationsMaximumdistancebetweentwoantennasforLOSpropagation:h1=heightofantennaoneh2=heightofantennatwo第15頁，課件共36頁，創(chuàng)作于2023年2月LOSWirelessTransmissionImpairmentsAttenuationandattenuationdistortionFreespacelossNoiseAtmosphericabsorptionMultipathRefractionThermalnoise第16頁，課件共36頁，創(chuàng)作于2023年2月AttenuationStrengthofsignalfallsoffwithdistanceovertransmissionmediumAttenuationfactorsforunguidedmedia:ReceivedsignalmusthavesufficientstrengthsothatcircuitryinthereceivercaninterpretthesignalSignalmustmaintainalevelsufficientlyhigherthannoisetobereceivedwithouterrorAttenuationisgreaterathigherfrequencies,causingdistortion第17頁，課件共36頁，創(chuàng)作于2023年2月FreeSpaceLossFreespaceloss,idealisotropicantennaPt=signalpowerattransmittingantennaPr=signalpoweratreceivingantenna=carrierwavelengthd=propagationdistancebetweenantennasc=speedoflight(?3′108m/s)wheredandareinthesameunits(e.g.,meters)第18頁，課件共36頁，創(chuàng)作于2023年2月FreeSpaceLossFreespacelossequationcanberecast:第19頁，課件共36頁，創(chuàng)作于2023年2月FreeSpaceLossFreespacelossaccountingforgainofotherantennasGt=gainoftransmittingantennaGr=gainofreceivingantennaAt=effectiveareaoftransmittingantennaAr=effectiveareaofreceivingantenna第20頁，課件共36頁，創(chuàng)作于2023年2月FreeSpaceLossFreespacelossaccountingforgainofotherantennascanberecastas第21頁，課件共36頁，創(chuàng)作于2023年2月CategoriesofNoiseThermalNoiseIntermodulationnoiseCrosstalkImpulseNoise第22頁，課件共36頁，創(chuàng)作于2023年2月ThermalNoiseThermalnoiseduetoagitationofelectronsPresentinallelectronicdevicesandtransmissionmediaCannotbeeliminatedFunctionoftemperatureParticularlysignificantforsatellitecommunication第23頁，課件共36頁，創(chuàng)作于2023年2月ThermalNoiseAmountofthermalnoisetobefoundinabandwidthof1Hzinanydeviceorconductoris:N0=noisepowerdensityinwattsper1Hzofbandwidthk=Boltzmann'sconstant=1.3803′10-23J/KT=temperature,inkelvins(absolutetemperature)第24頁，課件共36頁，創(chuàng)作于2023年2月ThermalNoiseNoiseisassumedtobeindependentoffrequencyThermalnoisepresentinabandwidthofBHertz(inwatts):or,indecibel-watts第25頁，課件共36頁，創(chuàng)作于2023年2月NoiseTerminologyIntermodulationnoise–occursifsignalswithdifferentfrequenciessharethesamemediumInterferencecausedbyasignalproducedatafrequencythatisthesumordifferenceoforiginalfrequenciesCrosstalk–unwantedcouplingbetweensignalpathsImpulsenoise–irregularpulsesornoisespikesShortdurationandofrelativelyhighamplitudeCausedbyexternalelectromagneticdisturbances,orfaultsandflawsinthecommunicationssystem第26頁，課件共36頁，創(chuàng)作于2023年2月ExpressionEb/N0RatioofsignalenergyperbittonoisepowerdensityperHertzThebiterrorratefordigitaldataisafunctionofEb/N0GivenavalueforEb/N0toachieveadesirederrorrate,parametersofthisformulacanbeselectedAsbitrateRincreases,transmittedsignalpowermustincreasetomaintainrequiredEb/N0第27頁，課件共36頁，創(chuàng)作于2023年2月OtherImpairmentsAtmosphericabsorption–watervaporandoxygencontributetoattenuationMultipath–obstaclesreflectsignalssothatmultiplecopieswithvaryingdelaysarereceivedRefraction–bendingofradiowavesastheypropagatethroughtheatmosphere第28頁，課件共36頁，創(chuàng)作于2023年2月MultipathPropagation第29頁，課件共36頁，創(chuàng)作于2023年2月MultipathPropagationReflection-occurswhensignalencountersasurfacethatislargerelativetothewavelengthofthesignalDiffraction-occursattheedgeofanimpenetrablebodythatislargecomparedtowavelengthofradiowaveScattering–occurswhenincomingsignalhitsanobjectwhosesizeintheorderofthewavelengthofthesignalorless第30頁，課件共36頁，創(chuàng)作于2023年2月TheEffectsofMultipathPropagationMultiplecopiesofasignalmayarriveatdifferentphasesIfphasesadddestructively,thesignallevelrelativetonoisedeclines,makingdetectionmoredifficultIntersymbolinterference(ISI)Oneormoredelayedcopiesofapulsemayarriveatthesametimeastheprimarypulseforasubsequentbit第31頁，課件共36頁，創(chuàng)作于2023年2月TypesofFadingFastfadingSlowfadingFlatfadingSelectivefadingRayleighfadingRicianfading第32頁，課件共36頁，創(chuàng)作于2023年2月ErrorCompensationMechanismsForwarderrorcorrectionAdaptiveequalizationDiversitytechniques第33頁，課件共36頁，創(chuàng)作于2023年2月ForwardErrorCorrectionTransmitteraddserror-correctingcodetodatablockCodeisafunctionofthedatabitsReceivercalculateserror-correctingcodefromincomingdatabitsIfcalculatedcodematchesincomingcode,noerroroccurredIferror-correctingcodesdon’tmatch,receiverattemptstodeterminebitsi