电子科大,信号与系统课件chap8.ppt

* Chapter 8 Communication Systems Chapter 8 Communication Systems Communication Channel 信道 Source Signals Modulator 调制器 Modulated Signals Be best suited for transmitting Chapter 8 Communication Systems Modulation : The general process of embedding an information -bearing signal into a second signal. Extracting the information-bearing signal. Demodulation : Modulation : Amplitude Modulation (AM) Frequency Modulation (FM) Phase Modulation (PM) Modulating Signal Carrier Signal Modulated Signal Amplitude Modulation Chapter 8 Communication Systems §8.1 Complex Exponential and Sinusoidal Amplitude Modulation §8.1.1 Amplitude Modulation with a Complex Exponential Carrier ——carrier frequency ——initial phase Modulation : Demodulation : Chapter 8 Communication Systems §8.1.2 Amplitude Modulation with a Sinusoidal Carrier Modulation : Chapter 8 Communication Systems Demodulation Synchronous Demodulation （同步解调） Asynchronous Demodulation （非同步解调） Chapter 8 Communication Systems Envelope Chapter 8 Communication Systems Communication Channel §8.2.1 Synchronous Demodulation Transmitter Modulation Receiver Synchronous Demodulation LPF same LPF Chapter 8 Communication Systems Suppose the modulator and demodulator are not synchronized in phase. Transmitter Carrier ① Complex Exponential Carrier Receiver Carrier When , Chapter 8 Communication Systems ② Sinusoidal Carrier Transmitter Carrier Receiver Carrier Modulation Demodulation The output of LPF i