無線通信與網(wǎng)絡(luò)chap6課件_第1頁
無線通信與網(wǎng)絡(luò)chap6課件_第2頁
無線通信與網(wǎng)絡(luò)chap6課件_第3頁
無線通信與網(wǎng)絡(luò)chap6課件_第4頁
無線通信與網(wǎng)絡(luò)chap6課件_第5頁
已閱讀5頁，還剩81頁未讀， 繼續(xù)免費閱讀

下載本文檔

版權(quán)說明：本文檔由用戶提供并上傳，收益歸屬內(nèi)容提供方，若內(nèi)容存在侵權(quán)，請進行舉報或認領(lǐng)

文檔簡介

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

溫馨提示

  • 1. 本站所有資源如無特殊說明，都需要本地電腦安裝OFFICE2007和PDF閱讀器。圖紙軟件為CAD,CAXA,PROE,UG,SolidWorks等.壓縮文件請下載最新的WinRAR軟件解壓。
  • 2. 本站的文檔不包含任何第三方提供的附件圖紙等，如果需要附件，請聯(lián)系上傳者。文件的所有權(quán)益歸上傳用戶所有。
  • 3. 本站RAR壓縮包中若帶圖紙，網(wǎng)頁內(nèi)容里面會有圖紙預(yù)覽，若沒有圖紙預(yù)覽就沒有圖紙。
  • 4. 未經(jīng)權(quán)益所有人同意不得將文件中的內(nèi)容挪作商業(yè)或盈利用途。
  • 5. 人人文庫網(wǎng)僅提供信息存儲空間，僅對用戶上傳內(nèi)容的表現(xiàn)方式做保護處理，對用戶上傳分享的文檔內(nèi)容本身不做任何修改或編輯，并不能對任何下載內(nèi)容負責。
  • 6. 下載文件中如有侵權(quán)或不適當內(nèi)容，請與我們聯(lián)系，我們立即糾正。
  • 7. 本站不保證下載資源的準確性、安全性和完整性, 同時也不承擔用戶因使用這些下載資源對自己和他人造成任何形式的傷害或損失。

評論

0/150

提交評論