通讯工程英文版.ppt

ECE4371 Fall 2014IntroductiontoTelecommunicationEngineering TelecommunicationLaboratory ZhuHanDepartmentofElectricalandComputerEngineeringClass4Sep 8th 2014 Overview Homework4 2 1 4 2 3 4 2 5 4 2 7 4 2 94 3 3 4 3 84 4 2 4 4 44 5 24 8 1Due9 22 14Phase lockedloopFMbasics CarrierRecoverError DSB e t 2m t cos wct cos wc w t e t m t cos w t Phaseerror iffixed attenuation Ifnot shortwaveradioFrequencyerror catastrophicbeatingeffectSSB onlyfrequencychanges f 30Hz DonaldDuckEffectCrystaloscillator atomsoscillator GPS Pilot asignal usuallyasinglefrequency transmittedoveracommunicationssystemforsupervisory control equalization continuity synchronization orreferencepurposes Phase LockedLoop Canbeawholecourse Themostimportantpartofreceiver Definition aclosed loopfeedbackcontrolsystemthatgeneratesandoutputsasignalinrelationtothefrequencyandphaseofaninput reference signalAphase lockedloopcircuitrespondsbothtothefrequencyandphaseoftheinputsignals automaticallyraisingorloweringthefrequencyofacontrolledoscillatoruntilitismatchedtothereferenceinbothfrequencyandphase VoltageControlledOscillator VCO W t wc ce0 t wherewcisthefree runningfrequencyExample IdealModel ModelSi Acos wct 1 t Sv Avcos wct c t Sp 0 5AAv sin 2wct 1 c sin 1 c So 0 5AAvsin 1 c AAv 1 c CaptureRangeandLockRange LPF VCO CarrierAcquisitioninDSB SC SignalSquaringmethodCostasLoopSSB SCnotworking Costasreceiver PLLApplications Clockrecovery nopilotDeskewing circuitdesignClockgeneration DirectDigitalSynthesisSpreadspectrum JitterNoiseReductionClockdistribution FMBasics VHF 30M 300M high fidelitybroadcastWidebandFM FMTV narrowbandFM two wayradio 1933FMandanglemodulationproposedbyArmstrong butsuccessby1949 Digital FrequencyShiftKey FSK PhaseShiftKey BPSK QPSK 8PSK AM FM Transversewave Longitudinalwave AngleModulationvs AM Summarize propertiesofamplitudemodulationAmplitudemodulationislinearjustmovetonewfrequencyband spectrumshapedoesnotchange Nonewfrequenciesgenerated Spectrum S f isatranslatedversionofM f Bandwidth 2WPropertiesofanglemodulationTheyarenonlinearspectrumshapedoeschange newfrequenciesgenerated S f isnotjustatranslatedversionofM f Bandwidthisusuallymuchlargerthan2W AngleModulationPro ConApplication Whyneedanglemodulation BetternoisereductionImprovedsystemfidelityDisadvantagesLowbandwidthefficiencyCompleximplementationsApplicationsFMradiobroadcastTVsoundsignalTwo waymobileradioCellularradioMicrowaveandsatellitecommunications InstantaneousFrequency Anglemodulationhastwoforms Frequencymodulation FM messageisrepresentedasthevariationoftheinstantaneousfrequencyofacarrier Phasemodulation PM messageisrepresentedasthevariationoftheinstantaneousphaseofacarrier PhaseModulation PM phasemodulation signal FrequencyModulation FM frequencymodulation signal Assumezeroinitialphase FMCharacteristics CharacteristicsofFMsignalsZero crossingsarenotregularEnvelopeisconstantFMandPMsignalsaresimilar RelationsbetweenFMandPM FM PMExample Time FM PMExample Frequency fc 1000 Ac 1 carrierfrequency Hz andmagnitudefm 250 Am 0 1 messagefrequency Hz andmagnitudek 4 modulationparameter generagesingletonemessagesignalt 0 1 10000 0 02 timewithsamplingat10KHzmt Am cos 2 pi fm t messagesignal Phasemodulationsp Ac cos 2 pi fc t 2 pi k mt Frequencymodulationdmt Am sin 2 pi fm t integrationsf Ac cos 2 pi fc t 2 pi k dmt PM Plotthesignalsubplot 311 plot t mt b grid title messagem t subplot 312 plot t sf r grid ylabel FMs t subplot 313 plot t sp m grid ylabel PMs t Matlab spectrumw 0 length t 1 length t 0 5 10000 Pm abs fftshift fft mt spectrumofmessagePp abs fftshift fft sp spectrumofPMsignalPf abs fftshift fft sf spectrumofFMsignal plotthespectrumsfigure 2 subplot 311 plot w Pm b axis 30003000min Pm max Pm grid title messagespectrumM f subplot 312 plot w Pf r axis 30003000min Pf max Pf grid ylabel FMS f subplot 313 plot w Pp m axis 30003000min Pp max Pp grid ylabel PMS f Matlab FrequencyModulation FM frequencymodulation signal Assumezeroinitialphase Example m t 0T2T Considerm t asquarewave asshown TheFMwaveforthism t isshownbelow FrequencyDeviation Frequencydeviation fdifferencebetweenthemaximuminstantaneousandcarrierfrequencyDefinition RelationshipwithinstantaneousfrequencyQuestion Isbandwidthofs t just2 f No instantaneousfrequencyisnotequivalenttospectrumfrequency withnon zeropower S t has spectrumfrequency withnon zeropower ModulationIndex Indicatebyhowmuchthemodulatedvariable instantaneousfrequency variesarounditsunmodulatedlevel messagefrequency Bandwidth A NarrowBandAngleModulation Definition Equation ComparisonwithAMOnlyphasedifferenceofPi 2Frequency similarTime AM frequencyconstantFM amplitudeconstantConclusion NBFMsignalissimilartoAMsignalNBFMhasalsobandwidth2W twicemessagesignalbandwidth Example BlockdiagramofamethodforgeneratinganarrowbandFMsignal AphasorcomparisonofnarrowbandFMandAMwavesforsinusoidalmodulation a NarrowbandFMwave b AMwave WideBandFM WidebandFMsignalFourierseriesrepresentation Example BesselFunctionofFirstKind SpectrumofWBFM Chapter5 2 Spectrumwhenm t issingle toneExample2 2 SpectrumProperties BandwidthofFM FactsFMhassidefrequenciesextendingtoinfinitefrequency theoreticallyinfinitebandwidthButsidefrequenciesbecomenegligiblysmallbeyondapoint practicallyfinitebandwidthFMsignalbandw