Transcription of Chapter 14
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Chapter 14
Chapter14 MODULATIONINTRODUCTIONA swehaveseeninpreviousthreechapters, ,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) atechniquecalled675676 ThePhysicalLayerofCommunicationsSystemso rthogonalfrequencydivisionmultiplexing(O FDM). , , (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 …
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