现代通信原理课件ChapterOne(1)

1现代通信原理课件ChapterOne2IntroductionChapterOneWhy?InformationAgeInformationSuperhighway3Applicationmilitaryapplication;commonapplication;ChapterOne4Whatisacommunicationsystem?Communicationsystemsisusedtotransmitinformation.1.1Introduction5Keyconceptionsorwords(1)Information;(2)Message;(3)Signal;(4)Waveforms1.1Introduction61JimesC.Maxwell（1864）2HeinrichHertz（1887）3ClaudeE.Shannon(1948)4.Winner1.1Introduction7PerspectiveofcommunicationWireoptic-fiberandnetworkswireless1G-2G-3G-B3GWLAN;MIMOandMIMO-OFDM,UWB,optic–wirelesscommunication1.1Introduction8Whatmustbeconsideredwhenyoudesignacommunicationsystem?1.Selectionoftheinformation-bearingwaveform2.Bandwidthandpowerofthewaveform3.Effectofsystemnoiseonthereceivedinformation4.Costofthesystem1.1Introduction91.2DigitalandAnalogsourceandsystem•ThegenerationofcommunicationsystemTransmitterInformationinputm(t)SignalprocessingchannelSignalprocessingCarriercircuitsReceivernoiseCarriercircuitsInformationoutput101)signalprocessorInanalogsystemitmaybeananaloglow-passfilter;Inhybridone,itmaybeanalog-to-digitalconverter(ADC)2)Functionofsignal-processingblockinhybridoneSourcecodingChannelcoding(addingparityandothers)3)FunctionofCarrierCircuitsmodulationFunctionoftransmitter111）Classification:wireandwirelessWirechannelincludingtwisted-pairtelephoneline/Coaxialcables,waveguidesandfiber-opticcablesWirelesschannelhavingair,vacuumandseawater2)Note:Thegeneralprinciplesofdigitalandanalogmodulationapplytoalltypesofchannels,althoughchannelcharacteristicsmayimposeconstraintsthatfavoraparticulartypeofsignalingChannel12Thereceivertakesthecorruptedsignalatthechanneloutputandconvertsittoabasebandsignalthatcanbehandledbythereceiverbasebandprocessor,andthenthereceiverbasebandprocessorestimatethesourceinformationandoutputtheestimationresultReceiver13Thegoalistodesigncommunicationsystemthattransmitinformationtothereceiverwithaslittledeteriorationaspossiblewhilesatisfyingdesignconstrainssuchasallowabletransmittedenergy,allowablesignalbandwidthandcost.Indigitalsystemmeasureofdeteriorationistakentobebiterrorrate(BER),whileinanalogsystemtheperformancemeasureisusuallytakentobethesignal-to-noiseratio(SNR)atthereceiveroutput.Summary141.2DigitalandAnalogsourceandsystem•ModelofanalogcommunicationsystemTransmittingendInformationsourcemodulatorchannelDemodu-latorSinkOr(acceptant)Receivingendnoise151.2DigitalandAnalogsourceandsystem(modelofdigitalcommunicationsystem)161）Relativelyinexpensivedigitalcircuitsmaybeused2）Privacyispreservedbyusingdataencryption3）Greaterdynamicrangeispossible4）Datafromdifferentsourcesmybetransmittedoveracommondigitaltransmissionsystem2theadvantageofdigitalsystem1.2DigitalandAnalogsourceandsystem175）Noisedoesnotaccumulateinlong-distancesystemsbyrepeater6）Errorindetecteddatamaybesmall,eveninlargeamountofnoiseonthereceivedsignal7）Errormayoftenbecorrectedbytheuseofcoding2theadvantageofdigitalsystem1.2DigitalandAnalogsourceandsystem181)Morebandwidthisrequiredgenerally2)Sychronizationisrequired3.DisadvantagesofDigitalcommunication1.2DigitalandAnalogsourceandsystem191.2DigitalandAnalogsourceandsystem(classificationofcommunicationsystem)accordingtophysicalpropertiesofinformation:Telephone/data/imageandsoonaccordingtofrequency:basebandtransmitting/bandpasstransmittingsystemaccordingtotransmittingmedium:wire/wirelessaccordingtomultiplexingpatterm:Frequencydivisionmultiplexingaccess(FDMA)Timedivisionmultiplexingaccess(TDMS)Codedivisionmultiplexingaccess(CDMA)201.2DigitalandAnalogsourceandsystem•Classificationofcommunicationpatterm•Peertopeercommunication:simplex;halfduplex;duplex•Paralleltransmittingcommunication•Seriestransmittingcommunication211.KeyconceptionDigitalinformationsourceproducesafinitesetofpossiblemessages.SuchastypewriterandkeyboardAnaloginformationsourceproducesmessagesthataredefinedoncontinuum.Digitalcommunicationsystemtransfersinformationfromadigitalsourcetotheintendedreceiver(sink)Analogcommunicationsystemtransfersinformationfromaanalogsourcetotheintendedreceiver(sink)1.2DigitalandAnalogsourceandsystem221)DeterministicwaveformItcanbemodeledasacompletelyspecifiedfunctionoftime2)Randomwaveform(stochasticwaveform)Itcannotbecompletelyspecifiedasafunctionoftimeandmustbemodeledprobabilistically1)Example:1.3DeterministicandRandomwaveforms)cos()(00tAt231)Propertyofthebooka.fromeasinesstodifficultyb.fromconcepttoperformanceanalysis2)Methodsoflearningita.readingitagainandagainb.graspingtheimportantconceptc.understandingthebasiccommunicationsystembyderivingsomekeyformulad.simulationusingMatlab1.4Thepropertyofthebookandmethodsoflearningit241.InformationContentIftheprobabiltiyoftransmittingjthmessageisPj，theinformationcontentsentfromadigitalsourcewhenitwastransmittedisgivenby:1.9InformationMeasurebitPPIjjj)(log)1(log22251.9InformationMeasureFromthedefinition,wehavethefollowingresults:1)Themessagethatarelesslikelytooccurprovidemoreinformation2)Informationcontentdependsononlythelikehoodofsendingthemessageanddoesnotdependonpossibleinterpretationofthecontentastowhetherornotitmakesse