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1、Chapter1IntroductionAcommunicationslinkorchannelconsistsofasourceofinformation,transmitterelectronicsincludingmodulators,mixers,poweramplifiers,orothercomponents,atransmittingantennaorarray,thepropagationenvironment,areceivingantennaorarrayandassociatedreceiverele
2、ctronics,andsignalprocessingtodetectanddecodeinformationfromthereceivedsignal.Thepurposeofthisbookistodeveloptheanalyticaltoolsrequiredforanend-to-endmodelofsuchacommunicationslink,includingantennaandpropagationeffectsaswellassignalprocessing.Thekeyfiguresofmeritf
3、orthecommunicationslinkarethesignaltonoiseratio(SNR)andchannelcapacity.Channelcapacityisthemaximumbitratethatcanbereliablysentfromtransmittertoreceiver.Forasinglecommunicationschannel,thecapacityisdeterminedbythebandwidthofthechannelandthesignaltonoiseratio(SNR)a
4、tthereceiveroutput,whichisinfluencedbythefollowingfactors:Transmitter:Totalradiatedpower,antennaradiationpattern,gain,andpolarization.Propagationenvironment:Distancebetweentransmitterandreceiver,multipath,blockage,loss,noise,andinterference.Receiver:Antennacharact
5、eristics,amplifiersandreceiverelectronics,andsignalprocessing.Thegoalistounderstandeachoftheseaspectsoftheelectromagneticpropagationchannelandtomodeltheoverallperformanceofacommunicationschannelintermsofthetransmittercharacteristics,propagationenvironment,andrecei
6、versystem.Inordertodevelopacompletechannelmodel,wemustconsiderantennatheoryforbothtransmittingandreceivingantennas,specificantennatypesandarrayantennas,noisetheory,propagationchannels,andcommunicationtheoryforbothsingleantennasandmulti-antennasystems.Thiswillprovi
7、dethetoolsnecessarytodeterminetheSNRattheoutputofacommunicationslink,thechannelcapacity,andthebiterrorraterealizedwiththechannelforaspecificmodulationscheme.Thesetoolswillalsoallowsynthesisofacommunicationssystemwhichmeetsadesiredperformancecriterion.1.1LinkBudget
8、AnalysisAsimpletoolforpropagationanalysisisalinkbudget,whichistherelationshipbetweenthetotaltransmittedpowerandthesignalpoweratthereceiveroutputintermsofantenn
