AmplitudeModulation(partfour)EE202DepartmentofElectronicsandElectricalEngineeringXi’anJiaotong–LiverpoolUniversity
LecturefiveVestigialSideBand(VSB)BasebandrepresentationofModulatedWavesandBand-passfilters
VSBSSBworksokforaninformation-bearingsignalwithanenergygapcenteredaroundzerofrequency.Howeverthespectraofwidebandsignals(e.g.videosignal)containsignificantlowfrequency.DSB-AMfIdealhighpassfilterLeakssomeofthelowersidebandInsteadofcompleteremovingasideband,avestigeofthatsidebandistransmitted,thusresultsinthebandwidthofaVSBmodulatedsignalisBT=fv+WWherefvisthevestigebandwidth.
VSBmodulatorH(f)isthetransferfunctionoftheoftheVSBshapingfilter,whichsatisfiesH(f+fc)+H(f-fc)=1(-wfw)
VSB:coherentdetection
ClassactivityDrillproblemVerifytheoutputsfromthereceiverareasindicatedinthefigure,assumingperfectsynchronizationbetweenthetransmitterandthereceiver.
VestigialSideBand(VSB)VSBismainlyusedinanalogueTVbroadcastingfortheirvideotransmissions.TVsignalconsistsofAudiosignal–transmittedbyFMVideosignal–transmittedbyVSBAvideosignalconsistsarangeoffrequencyandfmax=4.5MHz.IfittransmittedusingconventionalAM,therequiredBWis9MHz(BW=2fm).Butaccordingtothestandard,TVsignalislimitedto7MHzonlySo,toreducetheBW,apartoftheLSBofpicturesignalisnotfullytransmitted.
VestigialSideBand(VSB)ThefrequencyspectrumfortheTVsignal/VSB:LowerVideoBandsUpperVideoBandsTotalTVsignalbandwidth=7MHzVideoCarrierAudioCarrier4.5MHzUpperAudioBandsLowerAudioBands1.25Mhz5.75Mhzf(MHz)
Base-bandrepresentationofmodulatedsignals
ExamplegivenbySSB-AM
ClassActivityProvethefollowingrelationcanbeobtainedfortheschematicbelow:
Tips: