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1、ModulationEvanEverettandMichaelWuELEC433-Spring2013QuestionsfromLab1?Modulationx(t)=Asin(ωt+φ)CarrierData10100Modulation?Goal:overlaydataontocarriersignal(sinusoid)?Sinusoidshavetwoveryaccessibleparameters?ModulateamplitudeandphaseModulation1)InterferenceavoidanceW
2、hynot?2)Highfreq→smallantennasData10100Modulation?Goal:overlaydataontocarriersignal(sinusoid)?Sinusoidshavetwoveryaccessibleparameters?ModulateamplitudeandphaseSignalRepresentation:Phasor?Polar:Amplitude&Phase?Rectangular:“In-phase”(I)&“Quadrature”(Q)π/2QAmplitudeI
3、m[x]Phaseπ0IRe[x]-π/2x(t)=Asin(ωt+φ)x(t)=Icos(ωt)+Qsin(ωt)I=Asin(φ)Q=Acos(φ)SignalRepresentation?Rectangular(I,Q)formsuggestsapracticalimplementationIQIm[x]Icos(ωt)Re[x]10100Icos(ωt)+Qsin(ωt)90?sin(ωt)Q?Modulation=mappingdatabitsto(I,Q)valuesDigitalModulation[01][1
4、0][00][11]?Mapsbitstocomplexvalues(I/Q)(focusoftheLab3)?Complexmodulatedvaluesarecalled“symbols”?Setofsymbolsiscalled“constellation”or“alphabet”?#ofsymbolsinconstellationis“modulationorder”,M?M-orderconstellationcanencode______bitspersymbolDigitalModulation[01][10]
5、[00][11]?Mapsbitstocomplexvalues(I/Q)(focusoftheLab2)?Complexmodulatedvaluesarecalled“symbols”?Setofsymbolsiscalled“constellation”or“alphabet”?#ofsymbolsinconstellationis“modulationorder”,M?M-orderconstellationcanencodelog2(M)bitspersymbolPhaseShiftKeying(PSK)?Enco
6、desinformationonlyinphaseBPSK(M=2)QPSK(M=4)8-PSK(M=8)[000][001][00][01][0][1][10][11]?Constantpowerenvelope?Pros:noneedtorecoveramplitude,noneedforlinearampli?er?Con:wastesamplitudedimensionQuadratureAmplitudeModulation(QAM)?Encodesinformationinbothamplitudeandphas
7、e√√?(I,Q)grid∈M×M4-QAM16-QAM64-QAM?Commoninwidebandsystems:802.11b802.11g/n802.11ac16-QAM64-QAM256-QAMBit-to-SymbolMapping?Confusingwithneighborismostlikelyerror?Besttominimizebit-differencebetweenneighbors?GrayCoding?Neighboringsymbolsdifferbyonlyonebit?Extraperfo
8、rmanceatzerocost(thisisrare!)Natural-coded[01][10]Gray-coded[01][11]QPSKQPSK[00][11][00][10]Tradeoff:Ratevs.ErrorProbability?Byincreasingmodulati