Chapter 14

← Back to document page

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). , , (smallerwavelengths) , , ,thistimetoanintermediatefrequency(IF) (multiplexing).

Chapter 14 MODULATION INTRODUCTION ... for transmission act as filters that attenuate different frequencies by different values. So it is beneficial to move the spectrum of a signal to a frequency that is less susceptible to attenuation over a …

  Introduction, Chapter, Transmissions