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1、ModulationTechniquesMicrowaveandRFDesignofWirelessSystemsChapter9Dr.ZhangYonghongComparingwithtransmittingbasebandsignaldirectly,totransmitdatabymodulatingahigherfrequencycarrierwavehastheeffecton:①controllingtheradiatedfrequencyspectrum.②moreefficientuseoftheallocatedRFbandwidth.③flex
2、ibilityinaccommodatingdifferentbasebandsignalformats.AmplitudeFrequencyPhaseAMFMPMAnalogmodulation(varycontinuously)Digitalmodulation(changeindiscretesteps)①moreefficientuseoftheradiospectrum.②usuallyrequireslesspower.CDMA③overafadingcommunicationschannel.④morecompatiblewiththeuseoferr
3、orcorrectingcodes.Incontrasttoanalogmodulation,digitalmodulationhas:§9.1AnalogModulation§9.2BinaryDigitalModulation§9.3ErrorProbabilitiesforBinaryModulation§9.4EffectofRayleighFadingonBitErrorRats§9.5M-aryDigitalModulation§9.1AnalogModulationBasicanalogmodulation:AM(SSB,DSB),FM,PMPPM(P
4、ulsePositionModulation)isusedinUWB(ultrawideband)system.1.Signal-SidebandModulation2.DSB-SCModulation3.DSB-LCModulation4.EnvelopeDetectionofDSB-LCModulation5.FrequencyModulation(FM)1.Signal-SidebandModulationm(t):bandlimitedmodulatingwaveformfM:themaximumfrequencyofm(t)n0/2:two-sidedpo
5、werspectraldensityofGaussianwhitenoise.Contributedbythetransmitterchannelandnoisegeneratedbytheinputstagesofthereceiver.ThedemodulatorLOisidenticalinfrequencyandphasewiththemodulatorLO-synchronousorcoherentdemodulator.Inputsignalpower:Outputsignalpower:Inputnarrowbandnoisepower:Outputn
6、oisepower:TheoutputSNR:Conclusion:SSBdemodulatordoesnotdegradetheinputSNR.2.DSB-SCModulationDouble-sidebandsuppressedcarrier(DSB-SC)Conclusion:theDSB-SCdemodulatorimprovestheinputsignal-to-noiseratiobyafactoroftwo.FSSB=2FDSBButConclusion:ThecoherentSSBandDSB-SCdemodulatorshavethesameSN
7、Rperformance.3.DSB-LCModulationAdvantage:thecarriersignalcanbeusedasareferencesignaltophase-lookthelocaloscillatortosynchronizationwiththeincomingsignal.Double-SidebandLarge-Carrier(DSB-LC)Disadvantage:thecarrierpowerincreasesthetotalinputpowerbutdoesnotcontainanymodulationinformatio