1、,8 Communication systems,8.1 Complex Exponential and Sinusoidal Amplitude Modulation,Modulating system model:,8. Communication Systems,x(t) - modulating signal c(t) - Carrier signal,8 Communication systems,8.1.1 Amplitude Modulation with Complex Exponential Carrier,Exponential carrier:,For convenien
2、ce, let c=0, so,Output signal(modulated signal):,(1) Modulation Theory,8 Communication systems,8 Communication systems,(1) Implementation,8 Communication systems,8.1.2 Amplitude Modulation with Sinusoidal signal,For convenience, choose c=0, so,8 Communication systems,8 Communication systems,8 Commun
3、ication systems,8.2 Demodulation for Sinusoidal AM,8.2.1 Synchronous demodulation,(1) Demodulation process,8 Communication systems,In frequency domain:,In time domain:,Expected signal:,8 Communication systems,8 Communication systems,(2) Synchronous problem,8 Communication systems,Time domain:,The output of lowpass filter:,Ideal output: x(t),When , it is referred to as synchronous demodulation.,8 Communication systems,8.2.2 Asynchronous demodulation,Amplitude-modulated signal:,8 Communication systems,8 Communication systems,Problem: 8.1 8.3 8.22 8.28,
