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1、 8 Communication systems8.1 Complex Exponential and Sinusoidal Amplitude ModulationModulating system model:8. Communication Systemsx(t)c(t)y(t)=x(t)c(t)x(t) - modulating signalc(t) - Carrier signal 8 Communication systems8.1.1 Amplitude Modulation with Complex Exponential CarrierExponential carrier:
2、For convenience, let c=0, soOutput signal(modulated signal):(1) Modulation Theory 8 Communication systems 8 Communication systems(1) Implementation 8 Communication systems8.1.2 Amplitude Modulation with Sinusoidal signalFor convenience, choose c=0, so 8 Communication systems 8 Communication systems
3、8 Communication systems8.2 Demodulation for Sinusoidal AM8.2.1 Synchronous demodulation(1) Demodulation process 8 Communication systemsIn frequency domain:In time domain:Expected signal: 8 Communication systems 8 Communication systems(2) Synchronous problem 8 Communication systemsTime domain:The output of lowpass filter:Ideal output: x(t)When , it is referred to as synchronous demodulation. 8 Communication systems8.2.2 Asynchronous demodulationAmplitude-modulated signal: 8 Communication systems 8 Communication systemsProblem: 8.1 8.3 8.22 8.28
