现代通信原理课件ChapterOne.ppt

1 现代通信原理课件ChapterOne 2 Introduction ChapterOne Why InformationAgeInformationSuperhighway 3 Applicationmilitaryapplication commonapplication ChapterOne 4 Whatisacommunicationsystem Communicationsystemsisusedtotransmitinformation 1 1Introduction 5 Keyconceptionsorwords 1 Information 2 Message 3 Signal 4 Waveforms 1 1Introduction 6 1JimesC Maxwell 1864 2HeinrichHertz 1887 ClaudeE Shannon 1948 4 Winner 1 1Introduction 7 PerspectiveofcommunicationWireoptic fiberandnetworkswireless1G 2G 3G B3GWLAN MIMOandMIMO OFDM UWB optic wirelesscommunication 1 1Introduction 8 Whatmustbeconsideredwhenyoudesignacommunicationsystem 1 Selectionoftheinformation bearingwaveform2 Bandwidthandpowerofthewaveform3 Effectofsystemnoiseonthereceivedinformation4 Costofthesystem 1 1Introduction 9 1 2DigitalandAnalogsourceandsystem Thegenerationofcommunicationsystem 10 signalprocessorInanalogsystemitmaybeananaloglow passfilter Inhybridone itmaybeanalog to digitalconverter ADC 2 Functionofsignal processingblockinhybridoneSourcecodingChannelcoding addingparityandothers 3 FunctionofCarrierCircuitsmodulation Functionoftransmitter 11 1 Classification wireandwirelessWirechannelincludingtwisted pairtelephoneline Coaxialcables waveguidesandfiber opticcablesWirelesschannelhavingair vacuumandseawater2 Note Thegeneralprinciplesofdigitalandanalogmodulationapplytoalltypesofchannels althoughchannelcharacteristicsmayimposeconstraintsthatfavoraparticulartypeofsignaling Channel 12 Thereceivertakesthecorruptedsignalatthechanneloutputandconvertsittoabasebandsignalthatcanbehandledbythereceiverbasebandprocessor andthenthereceiverbasebandprocessorestimatethesourceinformationandoutputtheestimationresult Receiver 13 Thegoalistodesigncommunicationsystemthattransmitinformationtothereceiverwithaslittledeteriorationaspossiblewhilesatisfyingdesignconstrainssuchasallowabletransmittedenergy allowablesignalbandwidthandcost Indigitalsystemmeasureofdeteriorationistakentobebiterrorrate BER whileinanalogsystemtheperformancemeasureisusuallytakentobethesignal to noiseratio SNR atthereceiveroutput Summary 14 1 2DigitalandAnalogsourceandsystem Modelofanalogcommunicationsystem 15 1 2DigitalandAnalogsourceandsystem modelofdigitalcommunicationsystem 16 1 Relativelyinexpensivedigitalcircuitsmaybeused2 Privacyispreservedbyusingdataencryption3 Greaterdynamicrangeispossible4 Datafromdifferentsourcesmybetransmittedoveracommondigitaltransmissionsystem 2theadvantageofdigitalsystem 1 2DigitalandAnalogsourceandsystem 17 5 Noisedoesnotaccumulateinlong distancesystemsbyrepeater6 Errorindetecteddatamaybesmall eveninlargeamountofnoiseonthereceivedsignal7 Errormayoftenbecorrectedbytheuseofcoding 2theadvantageofdigitalsystem 1 2DigitalandAnalogsourceandsystem 18 1 Morebandwidthisrequiredgenerally2 Sychronizationisrequired 3 DisadvantagesofDigitalcommunication 1 2DigitalandAnalogsourceandsystem 19 1 2DigitalandAnalogsourceandsystem classificationofcommunicationsystem accordingtophysicalpropertiesofinformation Telephone data imageandsoon accordingtofrequency basebandtransmitting bandpasstransmittingsystem accordingtotransmittingmedium wire wireless accordingtomultiplexingpatterm Frequencydivisionmultiplexingaccess FDMA Timedivisionmultiplexingaccess TDMS Codedivisionmultiplexingaccess CDMA 20 1 2DigitalandAnalogsourceandsystem Classificationofcommunicationpatterm Peertopeercommunication simplex halfduplex duplex ParalleltransmittingcommunicationSeriestransmittingcommunication 21 KeyconceptionDigitalinformationsourceproducesafinitesetofpossiblemessages SuchastypewriterandkeyboardAnaloginformationsourceproducesmessagesthataredefinedoncontinuum Digitalcommunicationsystemtransfersinformationfromadigitalsourcetotheintendedreceiver sink Analogcommunicationsystemtransfersinformationfromaanalogsourcetotheintendedreceiver sink 1 2DigitalandAnalogsourceandsystem 22 DeterministicwaveformItcanbemodeledasacompletelyspecifiedfunctionoftimeRandomwaveform stochasticwaveform ItcannotbecompletelyspecifiedasafunctionoftimeandmustbemodeledprobabilisticallyExample 1 3DeterministicandRandomwaveforms 23 1 Propertyofthebooka fromeasinesstodifficultyb fromconcepttoperformanceanalysis2 Methodsoflearningita readingitagainandagainb graspingtheimportantconceptc understandingthebasiccommunicationsystembyderivingsomekeyformulad simulationusingMatlab 1 4Thepropertyofthebookandmethodsoflearningit 24 1 InformationContentIftheprobabiltiyoftransmittingjthmessageisPj theinformationcontentsentfromadigitalsourcewhenitwastransmittedisgivenby 1 9InformationMeasure 25 1 9InformationMeasure Fromthedefinition wehavethefollowingresults ThemessagethatarelesslikelytooccurprovidemoreinformationInformationcontentdependsononlythelikehoodofsendingthemessageanddoesnotdependonpossibleinterpretationofthecontentastowhetherornotitmakessense 26 2Unitofinformation 1 9InformationMeasure 1 Bits NatsandHartley 27 2Unitofinformation 1 9InformationMeasure 2 RelationshipbetweenBit NatandHartley 28 DefinitionIftherearempossibledifferentsourcemessageinadigitalsource misfinite andPjistheprobabiltiyofsendingthejthmessage theentropy alsocalledaverageinformation is 1 9InformationMeasure 3 EntropyforDigitalSource 29 4Example1 1 Inastringof12symbols whereeachsymbolconsistisofoneoffourlevels thereare412differentcombinations words sinceeachlevelsisequallylikely andallthedifferentwordsequallylikely ThusPj 1 4 12 AndIj log2 1 1 4 12 12log2 4 24bits 1 9InformationMeasure 30 5SourceRate 1 9InformationMeasure SourceRateisdefinedas Example A1 2Atelephonetouch tonekeypadhasthedigits0to9withprobabilityofsendingbeing0 099each plus and withprobabilityofsendingbeing0 005each Ifthekeysarepressedatarateof2keys putethedatarateforthissource Solution Usingdefineabove whereT 1 2 0 5s key then 31 Fordigitalsystems theoptimumsystemmightbedefinedasthesystemthatminimizestheBERatthesystemoutputsubjecttoconstraintsontransmittedenergyandchannelbandwidth Thusbiterrorrateandsignalbandwidthareofprimeimportanceinthiscourse 1 10Channelcapacity Shannongiveschannelcapacityas 32 1 10Channelcapacity WhereBisthechannelbandwidthinhertz S Nisthesignal to noisepowerratioattheinputtothedigitalreceiver AndshowedthatiftherateofinformationR bits s waslessthanC theBERwouldapproachzero 33 Inanalogsystem theoptimumsystemmightbedefinedastheonethatachievesthelargestsignal to noiseratioatthereceiveroutput subjecttodesignconstraintssuchaschannelbandwidthandtransmittedpower Nyquistshowedthatifapulserepresentsonebitofdata noninterferingpulsecould