現(xiàn)代通信原理課件

現(xiàn)代通信原理課件ChapterOne第一頁，共三十六頁。1IntroductionChapterOneWhy?InformationAgeInformationSuperhighway第二頁，共三十六頁。2Applicationmilitaryapplication;commonapplication;

ChapterOne第三頁，共三十六頁。3Whatisacommunicationsystem?Communicationsystemsisusedtotransmitinformation.1.1Introduction第四頁，共三十六頁。4Keyconceptionsorwords(1)Information;(2)Message;(3)Signal;(4)Waveforms1.1Introduction第五頁，共三十六頁。51JimesC.Maxwell（1864）2HeinrichHertz（1887）ClaudeE.Shannon(1948)4.Winner1.1Introduction第六頁，共三十六頁。6PerspectiveofcommunicationWireoptic-fiberandnetworkswireless1G->2G->3G->B3GWLAN;MIMOandMIMO-OFDM,UWB,optic–wirelesscommunication1.1Introduction第七頁，共三十六頁。7Whatmustbeconsideredwhenyoudesignacommunicationsystem?1.Selectionoftheinformation-bearingwaveform2.Bandwidthandpowerofthewaveform3.Effectofsystemnoiseonthereceivedinformation4.Costofthesystem1.1Introduction第八頁，共三十六頁。81.2DigitalandAnalogsourceandsystemThegenerationofcommunicationsystem第九頁，共三十六頁。9signalprocessorInanalogsystemitmaybeananaloglow-passfilter;Inhybridone,itmaybeanalog-to-digitalconverter(ADC)2)Functionofsignal-processingblockinhybridoneSourcecodingChannelcoding(addingparityandothers)3)FunctionofCarrierCircuitsmodulationFunctionoftransmitter第十頁，共三十六頁。101）

Classification:wireandwirelessWirechannelincludingtwisted-pairtelephoneline/Coaxialcables,waveguidesandfiber-opticcables

Wirelesschannelhavingair,vacuumandseawater2)Note:Thegeneralprinciplesofdigitalandanalogmodulationapplytoalltypesofchannels,althoughchannelcharacteristicsmayimposeconstraintsthatfavoraparticulartypeofsignalingChannel第十一頁，共三十六頁。11Thereceivertakesthecorruptedsignalatthechanneloutputandconvertsittoabasebandsignalthatcanbehandledbythereceiverbasebandprocessor,andthenthereceiverbasebandprocessorestimatethesourceinformationandoutputtheestimationresultReceiver第十二頁，共三十六頁。12Thegoalistodesigncommunicationsystemthattransmitinformationtothereceiverwithaslittledeteriorationaspossiblewhilesatisfyingdesignconstrainssuchasallowabletransmittedenergy,allowablesignalbandwidthandcost.Indigitalsystemmeasureofdeteriorationistakentobebiterrorrate(BER),whileinanalogsystemtheperformancemeasureisusuallytakentobethesignal-to-noiseratio(SNR)atthereceiveroutput.Summary第十三頁，共三十六頁。131.2DigitalandAnalogsourceandsystemModelofanalogcommunicationsystem第十四頁，共三十六頁。141.2DigitalandAnalogsourceandsystem

(modelofdigitalcommunicationsystem)第十五頁，共三十六頁。151）Relativelyinexpensivedigitalcircuitsmaybeused2）Privacyispreservedbyusingdataencryption3）Greaterdynamicrangeispossible4）Datafromdifferentsourcesmybetransmittedoveracommondigitaltransmissionsystem2theadvantageofdigitalsystem1.2DigitalandAnalogsourceandsystem第十六頁，共三十六頁。165）Noisedoesnotaccumulateinlong-distancesystemsbyrepeater6）Errorindetecteddatamaybesmall,eveninlargeamountofnoiseonthereceivedsignal7）Errormayoftenbecorrectedbytheuseofcoding2theadvantageofdigitalsystem1.2DigitalandAnalogsourceandsystem第十七頁，共三十六頁。171)Morebandwidthisrequiredgenerally2)Sychronizationisrequired3.DisadvantagesofDigitalcommunication1.2DigitalandAnalogsourceandsystem第十八頁，共三十六頁。181.2DigitalandAnalogsourceandsystem

(classificationofcommunicationsystem)accordingtophysicalpropertiesofinformation:Telephone/data/imageandsoon

accordingtofrequency:basebandtransmitting/bandpasstransmittingsystem

accordingtotransmittingmedium:wire/wireless

accordingtomultiplexingpatterm:Frequencydivisionmultiplexingaccess(FDMA)Timedivisionmultiplexingaccess(TDMS)Codedivisionmultiplexingaccess(CDMA)第十九頁，共三十六頁。191.2DigitalandAnalogsourceandsystemClassificationofcommunicationpattermPeertopeercommunication:simplex;halfduplex;duplexParalleltransmittingcommunicationSeriestransmittingcommunication第二十頁，共三十六頁。20Keyconception

Digitalinformationsourceproducesafinitesetofpossiblemessages.Suchastypewriterandkeyboard

Analoginformationsourceproducesmessagesthataredefinedoncontinuum.

Digitalcommunicationsystemtransfersinformationfromadigitalsourcetotheintendedreceiver(sink)

Analogcommunicationsystemtransfersinformationfromaanalogsourcetotheintendedreceiver(sink)1.2DigitalandAnalogsourceandsystem第二十一頁，共三十六頁。21DeterministicwaveformItcanbemodeledasacompletelyspecifiedfunctionoftimeRandomwaveform(stochasticwaveform)ItcannotbecompletelyspecifiedasafunctionoftimeandmustbemodeledprobabilisticallyExample:

1.3DeterministicandRandomwaveforms

第二十二頁，共三十六頁。221)Propertyofthebooka.fromeasinesstodifficultyb.fromconcepttoperformanceanalysis2)Methodsoflearningita.readingitagainandagainb.graspingtheimportantconceptc.understandingthebasiccommunicationsystembyderivingsomekeyformulad.simulationusingMatlab1.4Thepropertyofthebookandmethodsoflearningit第二十三頁，共三十六頁。231.InformationContentIftheprobabiltiyoftransmittingjthmessageisPj，

theinformationcontentsentfromadigitalsourcewhenitwastransmittedisgivenby:1.9InformationMeasure第二十四頁，共三十六頁。241.9InformationMeasureFromthedefinition,wehavethefollowingresults:ThemessagethatarelesslikelytooccurprovidemoreinformationInformationcontentdependsononlythelikehoodofsendingthemessageanddoesnotdependonpossibleinterpretationofthecontentastowhetherornotitmakessense.第二十五頁，共三十六頁。252Unitofinformation1.9InformationMeasure1)Bits,NatsandHartley第二十六頁，共三十六頁。262Unitofinformation1.9InformationMeasure2)RelationshipbetweenBit,NatandHartley第二十七頁，共三十六頁。27Definition

Iftherearempossibledifferentsourcemessageinadigitalsource(misfinite),andPjistheprobabiltiyofsendingthejthmessage,theentropy(alsocalledaverageinformation)is:1.9InformationMeasure3.EntropyforDigitalSource第二十八頁，共三十六頁。284Example1-1:Inastringof12symbols,whereeachsymbolconsistisofoneoffourlevels,thereare412differentcombinations(words),sinceeachlevelsisequallylikely,andallthedifferentwordsequallylikely.ThusPj=(1/4)12,AndIj=log2(1/(1/4)12)=12log2(4)=24bits1.9InformationMeasure第二十九頁，共三十六頁。295SourceRate

1.9InformationMeasureSourceRateisdefinedasExample:A1-2Atelephonetouch-tonekeypadhasthedigits0to9withprobabilityofsendingbeing0.099each,plus“*”and“#”withprobabilityofsendingbeing0.005each.Ifthekeysarepressedatarateof2keys/putethedatarateforthissource.Solution:

Usingdefineabove,whereT=1/2=0.5s/key,then:第三十頁，共三十六頁。30Fordigitalsystems,theoptimumsystemmightbedefinedasthesystemthatminimizestheBERatthesystemoutputsubjecttoconstraintsontransmittedenergyandchannelbandwidth.Thusbiterrorrateandsignalbandwidthareofprimeimportanceinthiscourse.1.10ChannelcapacityShannongiveschannelcapacityas第三十一頁，共三十六頁。311.10ChannelcapacityWhereBisthechannelbandwidthinhertz,S/Nisthesignal-to-noisepowerratioattheinputtothedigitalreceiver.AndshowedthatiftherateofinformationR(bits/s)waslessthanC,theBERwouldapproachzero.第三十二頁，共三十六頁。32Inanalogsystem,theoptimumsystemmightbedefinedastheonethatachievesthelargestsignal-to-noiseratioatthereceiveroutput,subjecttodesignconstraintssuchaschannelbandwidthandtransmittedpower.Nyquistshowedthatifapulserepresentsonebitofdata,noninterferingpulsecouldbesentoverachannelnofasterthan2Bpulses/s,whereBisthechannelbandwidthinhertz.Thatisnowknownasthedimensionalitytheo