无线通信与网络chap6课件

SignalEncodingTechniquesChapter6SignalEncodingTechniquesChap1ReasonsforChoosingEncodingTechniquesDigitaldata,digitalsignalEquipmentlesscomplexandexpensivethandigital-to-analogmodulationequipmentAnalogdata,digitalsignalPermitsuseofmoderndigitaltransmissionandswitchingequipmentReasonsforChoosingEncodingReasonsforChoosingEncodingTechniquesDigitaldata,analogsignalSometransmissionmediawillonlypropagateanalogsignalsE.g.,opticalfiberandunguidedmediaAnalogdata,analogsignalAnalogdatainelectricalformcanbetransmittedeasilyandcheaplyDonewithvoicetransmissionovervoice-gradelinesReasonsforChoosingEncodingSignalEncodingCriteriaWhatdetermineshowsuccessfulareceiverwillbeininterpretinganincomingsignal?Signal-to-noiseratioDatarateBandwidthAnincreaseindatarateincreasesbiterrorrateAnincreaseinSNRdecreasesbiterrorrateAnincreaseinbandwidthallowsanincreaseindatarateSignalEncodingCriteriaWhatdFactorsUsedtoCompare

EncodingSchemesSignalspectrumWithlackofhigh-frequencycomponents,lessbandwidthrequiredWithnodccomponent,accouplingviatransformerpossibleTransferfunctionofachannelisworsenearbandedgesClockingEaseofdeterminingbeginningandendofeachbitpositionFactorsUsedtoCompare

EncodiFactorsUsedtoCompare

EncodingSchemesSignalinterferenceandnoiseimmunityPerformanceinthepresenceofnoiseCostandcomplexityThehigherthesignalratetoachieveagivendatarate,thegreaterthecostFactorsUsedtoCompare

EncodiBasicEncodingTechniquesDigitaldatatoanalogsignalAmplitude-shiftkeying(ASK)AmplitudedifferenceofcarrierfrequencyFrequency-shiftkeying(FSK)FrequencydifferencenearcarrierfrequencyPhase-shiftkeying(PSK)PhaseofcarriersignalshiftedBasicEncodingTechniquesDigitBasicEncodingTechniquesBasicEncodingTechniquesAmplitude-ShiftKeyingOnebinarydigitrepresentedbypresenceofcarrier,atconstantamplitudeOtherbinarydigitrepresentedbyabsenceofcarrierwherethecarriersignalisAcos(2πfct) Amplitude-ShiftKeyingOnebinaAmplitude-ShiftKeyingSusceptibletosuddengainchangesInefficientmodulationtechniqueOnvoice-gradelines,usedupto1200bpsUsedtotransmitdigitaldataoveropticalfiberAmplitude-ShiftKeyingSusceptiBinaryFrequency-ShiftKeying(BFSK)Twobinarydigitsrepresentedbytwodifferentfrequenciesnearthecarrierfrequencywheref1andf2areoffsetfromcarrierfrequencyfcbyequalbutoppositeamountsBinaryFrequency-ShiftKeyingBinaryFrequency-ShiftKeying(BFSK)LesssusceptibletoerrorthanASKOnvoice-gradelines,usedupto1200bpsUsedforhigh-frequency(3to30MHz)radiotransmissionCanbeusedathigherfrequenciesonLANsthatusecoaxialcableBinaryFrequency-ShiftKeyingMultipleFrequency-ShiftKeying(MFSK)MorethantwofrequenciesareusedMorebandwidthefficientbutmoresusceptibletoerrorfi

=fc

+(2i–1–M)fdfc

=thecarrierfrequencyfd

=thedifferencefrequencyM=numberofdifferentsignalelements=2LL=numberofbitspersignalelementMultipleFrequency-ShiftKeyinMultipleFrequency-ShiftKeying(MFSK)Tomatchdatarateofinputbitstream,eachoutputsignalelementisheldfor:Ts=LTsecondswhereTisthebitperiod(datarate=1/T)So,onesignalelementencodesLbitsMultipleFrequency-ShiftKeyinMultipleFrequency-ShiftKeying(MFSK)Totalbandwidthrequired2MfdMinimumfrequencyseparationrequired2fd=1/TsTherefore,modulatorrequiresabandwidthofWd=2L/LT=M/TsMultipleFrequency-ShiftKeyinMultipleFrequency-ShiftKeying(MFSK)MultipleFrequency-ShiftKeyinPhase-ShiftKeying(PSK)Two-levelPSK(BPSK)UsestwophasestorepresentbinarydigitsPhase-ShiftKeying(PSK)Two-lePhase-ShiftKeying(PSK)DifferentialPSK(DPSK)PhaseshiftwithreferencetopreviousbitBinary0–signalburstofsamephaseasprevioussignalburstBinary1–signalburstofoppositephasetoprevioussignalburstPhase-ShiftKeying(PSK)DifferPhase-ShiftKeying(PSK)Four-levelPSK(QPSK)EachelementrepresentsmorethanonebitPhase-ShiftKeying(PSK)Four-lPhase-ShiftKeying(PSK)MultilevelPSKUsingmultiplephaseangleswitheachanglehavingmorethanoneamplitude,multiplesignalselementscanbeachievedD=modulationrate,baudR=datarate,bpsM=numberofdifferentsignalelements=2LL=numberofbitspersignalelementPhase-ShiftKeying(PSK)MultilPerformanceBandwidthofmodulatedsignal(BT)ASK,PSK BT=(1+r)RFSK BT=2DF+(1+r)RR=bitrate0<r<1;relatedtohowsignalisfiltered

DF=f2-fc=fc-f1PerformanceBandwidthofmodulaPerformanceBandwidthofmodulatedsignal(BT)MPSKMFSKL=numberofbitsencodedpersignalelementM=numberofdifferentsignalelementsPerformanceBandwidthofmodulaQuadratureAmplitudeModulationQAMisacombinationofASKandPSKTwodifferentsignalssentsimultaneouslyonthesamecarrierfrequencyQuadratureAmplitudeModulatioQuadratureAmplitudeModulationQuadratureAmplitudeModulatioReasonsforAnalogModulationModulationofdigitalsignalsWhenonlyanalogtransmissionfacilitiesareavailable,digitaltoanalogconversionrequiredModulationofanalogsignalsAhigherfrequencymaybeneededforeffectivetransmissionModulationpermitsfrequencydivisionmultiplexingReasonsforAnalogModulationMBasicEncodingTechniquesAnalogdatatoanalogsignalAmplitudemodulation(AM)AnglemodulationFrequencymodulation(FM)Phasemodulation(PM)BasicEncodingTechniquesAnaloAmplitudeModulationAmplitudeModulationcos2fct=carrierx(t)=inputsignalna=modulationindexRatioofamplitudeofinputsignaltocarriera.k.adoublesidebandtransmittedcarrier(DSBTC)AmplitudeModulationAmplitudeSpectrumofAMsignalSpectrumofAMsignalAmplitudeModulationTransmittedpowerPt=totaltransmittedpowerins(t)Pc=transmittedpowerincarrierAmplitudeModulationTransmitteSingleSideband(SSB)VariantofAMissinglesideband(SSB)SendsonlyonesidebandEliminatesothersidebandandcarrierAdvantagesOnlyhalfthebandwidthisrequiredLesspowerisrequiredDisadvantagesSuppressedcarriercan’tbeusedforsynchronizationpurposesSingleSideband(SSB)VariantoAngleModulationAnglemodulationPhasemodulationPhaseisproportionaltomodulatingsignalnp=phasemodulationindexAngleModulationAnglemodulatiAngleModulationFrequencymodulationDerivativeofthephaseisproportionaltomodulatingsignalnf=frequencymodulationindexAngleModulationFrequencymoduAngleModulationComparedtoAM,FMandPMresultinasignalwhosebandwidth:isalsocenteredatfcbuthasamagnitudethatismuchdifferentAnglemodulationincludescos((t))whichproducesawiderangeoffrequenciesThus,FMandPMrequiregreaterbandwidththanAMAngleModulationComparedtoAMAngleModulationCarson’srulewhereTheformulaforFMbecomesAngleModulationCarson’sruleBasicEncodingTechniquesAnalogdatatodigitalsignalPulsecodemodulation(PCM)Deltamodulation(DM)BasicEncodingTechniquesAnaloAnalogDatatoDigitalSignalOnceanalogdatahavebeenconvertedtodigitalsignals,thedigitaldata:canbetransmittedusingNRZ-LcanbeencodedasadigitalsignalusingacodeotherthanNRZ-Lcanbeconvertedtoananalogsignal,usingpreviouslydiscussedtechniquesAnalogDatatoDigitalSignalOPulseCodeModulationBasedonthesamplingtheoremEachanalogsampleisassignedabinarycodeAnalogsamplesarereferredtoaspulseamplitudemodulation(PAM)samplesThedigitalsignalconsistsofblockofnbits,whereeachn-bitnumberistheamplitudeofaPCMpulsePulseCodeModulationBasedonPulseCodeModulationPulseCodeModulationPulseCodeModulationByquantizingthePAMpulse,originalsignalisonlyapproximatedLeadstoquantizingnoiseSignal-to-noiseratioforquantizingnoiseThus,eachadditionalbitincreasesSNRby6dB,orafactorof4PulseCodeModulationByquantiDeltaModulationAnaloginputisapproximatedbystaircasefunctionMovesupordownbyonequantizationlevel()ateachsamplingintervalThebitstreamapproximatesderivativeofanalogsignal(ratherthanamplitude)1isgeneratediffunctiongoesup0otherwiseDeltaModulationAnaloginputiDeltaModulationDeltaModulationDeltaModulationTwoimportantparametersSizeofstepassignedtoeachbinarydigit()SamplingrateAccuracyimprovedbyincreasingsamplingrateHowever,thisincreasesthedatarateAdvantageofDMoverPCMisthesimplicityofitsimplementationDeltaModulationTwoimportantReasonsforGrowthofDigitalTechniquesGrowthinpopularityofdigitaltechniquesforsendinganalogdataRepeatersareusedinsteadofamplifiersNoadditivenoiseTDMisusedinsteadofFDMNointermodulationnoiseConversiontodigitalsignalingallowsuseofmoreefficientdigitalswitchingtechniquesReasonsforGrowthofDigitalSignalEncodingTechniquesChapter6SignalEncodingTechniquesChap44ReasonsforChoosingEncodingTechniquesDigitaldata,digitalsignalEquipmentlesscomplexandexpensivethandigital-to-analogmodulationequipmentAnalogdata,digitalsignalPermitsuseofmoderndigitaltransmissionandswitchingequipmentReasonsforChoosingEncodingReasonsforChoosingEncodingTechniquesDigitaldata,analogsignalSometransmissionmediawillonlypropagateanalogsignalsE.g.,opticalfiberandunguidedmediaAnalogdata,analogsignalAnalogdatainelectricalformcanbetransmittedeasilyandcheaplyDonewithvoicetransmissionovervoice-gradelinesReasonsforChoosingEncodingSignalEncodingCriteriaWhatdetermineshowsuccessfulareceiverwillbeininterpretinganincomingsignal?Signal-to-noiseratioDatarateBandwidthAnincreaseindatarateincreasesbiterrorrateAnincreaseinSNRdecreasesbiterrorrateAnincreaseinbandwidthallowsanincreaseindatarateSignalEncodingCriteriaWhatdFactorsUsedtoCompare

EncodingSchemesSignalspectrumWithlackofhigh-frequencycomponents,lessbandwidthrequiredWithnodccomponent,accouplingviatransformerpossibleTransferfunctionofachannelisworsenearbandedgesClockingEaseofdeterminingbeginningandendofeachbitpositionFactorsUsedtoCompare

EncodiFactorsUsedtoCompare

EncodingSchemesSignalinterferenceandnoiseimmunityPerformanceinthepresenceofnoiseCostandcomplexityThehigherthesignalratetoachieveagivendatarate,thegreaterthecostFactorsUsedtoCompare

EncodiBasicEncodingTechniquesDigitaldatatoanalogsignalAmplitude-shiftkeying(ASK)AmplitudedifferenceofcarrierfrequencyFrequency-shiftkeying(FSK)FrequencydifferencenearcarrierfrequencyPhase-shiftkeying(PSK)PhaseofcarriersignalshiftedBasicEncodingTechniquesDigitBasicEncodingTechniquesBasicEncodingTechniquesAmplitude-ShiftKeyingOnebinarydigitrepresentedbypresenceofcarrier,atconstantamplitudeOtherbinarydigitrepresentedbyabsenceofcarrierwherethecarriersignalisAcos(2πfct) Amplitude-ShiftKeyingOnebinaAmplitude-ShiftKeyingSusceptibletosuddengainchangesInefficientmodulationtechniqueOnvoice-gradelines,usedupto1200bpsUsedtotransmitdigitaldataoveropticalfiberAmplitude-ShiftKeyingSusceptiBinaryFrequency-ShiftKeying(BFSK)Twobinarydigitsrepresentedbytwodifferentfrequenciesnearthecarrierfrequencywheref1andf2areoffsetfromcarrierfrequencyfcbyequalbutoppositeamountsBinaryFrequency-ShiftKeyingBinaryFrequency-ShiftKeying(BFSK)LesssusceptibletoerrorthanASKOnvoice-gradelines,usedupto1200bpsUsedforhigh-frequency(3to30MHz)radiotransmissionCanbeusedathigherfrequenciesonLANsthatusecoaxialcableBinaryFrequency-ShiftKeyingMultipleFrequency-ShiftKeying(MFSK)MorethantwofrequenciesareusedMorebandwidthefficientbutmoresusceptibletoerrorfi

=fc

+(2i–1–M)fdfc

=thecarrierfrequencyfd

=thedifferencefrequencyM=numberofdifferentsignalelements=2LL=numberofbitspersignalelementMultipleFrequency-ShiftKeyinMultipleFrequency-ShiftKeying(MFSK)Tomatchdatarateofinputbitstream,eachoutputsignalelementisheldfor:Ts=LTsecondswhereTisthebitperiod(datarate=1/T)So,onesignalelementencodesLbitsMultipleFrequency-ShiftKeyinMultipleFrequency-ShiftKeying(MFSK)Totalbandwidthrequired2MfdMinimumfrequencyseparationrequired2fd=1/TsTherefore,modulatorrequiresabandwidthofWd=2L/LT=M/TsMultipleFrequency-ShiftKeyinMultipleFrequency-ShiftKeying(MFSK)MultipleFrequency-ShiftKeyinPhase-ShiftKeying(PSK)Two-levelPSK(BPSK)UsestwophasestorepresentbinarydigitsPhase-ShiftKeying(PSK)Two-lePhase-ShiftKeying(PSK)DifferentialPSK(DPSK)PhaseshiftwithreferencetopreviousbitBinary0–signalburstofsamephaseasprevioussignalburstBinary1–signalburstofoppositephasetoprevioussignalburstPhase-ShiftKeying(PSK)DifferPhase-ShiftKeying(PSK)Four-levelPSK(QPSK)EachelementrepresentsmorethanonebitPhase-ShiftKeying(PSK)Four-lPhase-ShiftKeying(PSK)MultilevelPSKUsingmultiplephaseangleswitheachanglehavingmorethanoneamplitude,multiplesignalselementscanbeachievedD=modulationrate,baudR=datarate,bpsM=numberofdifferentsignalelements=2LL=numberofbitspersignalelementPhase-ShiftKeying(PSK)MultilPerformanceBandwidthofmodulatedsignal(BT)ASK,PSK BT=(1+r)RFSK BT=2DF+(1+r)RR=bitrate0<r<1;relatedtohowsignalisfiltered

DF=f2-fc=fc-f1PerformanceBandwidthofmodulaPerformanceBandwidthofmodulatedsignal(BT)MPSKMFSKL=numberofbitsencodedpersignalelementM=numberofdifferentsignalelementsPerformanceBandwidthofmodulaQuadratureAmplitudeModulationQAMisacombinationofASKandPSKTwodifferentsignalssentsimultaneouslyonthesamecarrierfrequencyQuadratureAmplitudeModulatioQuadratureAmplitudeModulationQuadratureAmplitudeModulatioReasonsforAnalogModulationModulationofdigitalsignalsWhenonlyanalogtransmissionfacilitiesareavailable,digitaltoanalogconversionrequiredModulationofanalogsignalsAhigherfrequencymaybeneededforeffectivetransmissionModulationpermitsfrequencydivisionmultiplexingReasonsforAnalogModulationMBasicEncodingTechniquesAnalogdatatoanalogsignalAmplitudemodulation(AM)AnglemodulationFrequencymodulation(FM)Phasemodulation(PM)BasicEncodingTechniquesAnaloAmplitudeModulationAmplitudeModulationcos2fct=carrierx(t)=inputsignalna=modulationindexRatioofamplitudeofinputsignaltocarriera.k.adoublesidebandtransmittedcarrier(DSBTC)AmplitudeModulationAmplitudeSpectrumofAMsignalSpectrumofAMsignalAmplitudeModulationTransmittedpowerPt=totaltransmittedpowerins(t)Pc=transmittedpowerincarrierAmplitudeModulationTransmitteSingleSideband(SSB)VariantofAMissinglesideband(SSB)SendsonlyonesidebandEliminatesothersidebandandcarrierAdvantagesOnlyhalfthebandwidthisrequiredLesspowerisrequiredDisadvantagesSuppressedcarriercan’tbeusedforsynchronizationpurposesSingleSideband(SSB)VariantoAngleModulationAnglemodulationPhasemodulationPhaseisproportionaltomodulatingsignalnp=phasemodulationindexAngleModulationAnglemodulatiAngleModulationFrequencymodulationDerivativeofthephaseisproportionaltomodulatingsignalnf=frequencymodulationindexAngleModulationFrequencymoduAngleModulationComparedtoAM,FMandPMresultinasignalwhosebandwidth:isalsocenteredatfcbuthasamagnitudethatismuchdifferentAnglemodulationincludescos((t))whichproducesawiderangeoffrequenciesThus,FMandPMrequiregreaterbandwidththanAMAngleModulationComparedtoAMAngleModulationCarson’srulewhereTheformulaforFMbecomesAngleModulationCarson’sruleBasicEncodingTechniquesAnalogdatatodigitalsignalPulsecodemodulation(PCM)Deltamodulation(DM)BasicEncodingTechniquesAnaloAnalogDatatoDigitalSignalO