Chapter 14

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Chapter14MODULATIONINTRODUCTIONAswehaves eeninpreviousthreechapters, ,thesourceinformationisimpresseduponacar rier-wave(essentiallyasinusoidofacertain frequency) ( ,audio,voltagepulsetraincarryingdigitali nformation) forexample,therepresentationofsampledsig nalsbytheamplitude, (2,6,9)thatwecanwritethissinusoidalcarri ersignalas:c(t)=Acos(2 fct+ )( )Here,Aiscalledtheamplitudeand ,dataareusedtomodulateorchangeitsamplitu de,frequency, , (digitalmodulation) ,wealsodescribeaspecialcaseofdigitalmodu lationthatisveryimportantfortransmission ofinformationusingmodems quadratureamplitudemodulation(QAM) atechniquecalled675676ThePhysicalLayerof CommunicationsSystemsorthogonalfrequency divisionmultiplexing(OFDM).

The two common forms of analog modulation are amplitude modulation (AM) and frequency modulation (FM) which is specific form of more general angle ... amplitude and phase mapping is called quadrature amplitude modulation (QAM). In analog modulation we were interested in the SNR, but recall from Chapter 10 ...

  Modulation, Amplitude, Quadrature, Quadrature amplitude modulation, Amplitude modulation