Chapter 8 Communication Systems
1 Chapter 8 Communication Systems
Chapter 8 Communication Systems Communication Channel 信道 日日日 ■■ Source Modulator Modulated Signals 1调制器 Signals Be best suited for transmitting 2
2 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 Demodulation: Extracting the information-bearing signal. Amplitude Modulation (AM) Modulation Frequency modulation (FM) Phase Modulation(PM) Modulating Modulated Signal x y()=x()x() Signal Carrier C Signal Amplitude modulation
3 Chapter 8 Communication Systems Modulation : The general process of embedding an information -bearing signal into a second signal. Demodulation : Extracting the information-bearing signal. Modulation : Amplitude Modulation (AM) Frequency Modulation (FM) Phase Modulation (PM) Modulating Signal Carrier Signal Modulated Signal x(t) y(t) = x(t)c(t) c(t) Amplitude Modulation
Chapter 8 Communication Systems 58.1 Complex Exponential and Sinusoidal Amplitude Modulation 1. c(o=el 2. c(t)=cos@ t t Envelope 4
4 Chapter 8 Communication Systems §8.1 Complex Exponential and Sinusoidal Amplitude Modulation 1. ( ) c j t c t e = 2. cos ( ) c c t t = t x(t) t y(t) Envelope
Chapter 8 Communication Systems 58.2. 1 Synchronous Demodulation O Complex Exponential Carrier ∞→·y() Communication( LPF x channel (a2+b) e (n+) Transmitter Receiver Modulation Synchronous Demodulation 1. Suppose the modulator and demodulator are not synchronized in phase. 2. Suppose the modulator and demodulator are not synchronized in frequency. 5
5 Chapter 8 Communication Systems 1. Suppose the modulator and demodulator are not synchronized in phase. ① Complex Exponential Carrier §8.2.1 Synchronous Demodulation j t ( c c ) e + x(t) y(t) Communication Channel Transmitter Modulation Receiver Synchronous Demodulation LPF x(t) w(t) j t ( d ) e − + 2. Suppose the modulator and demodulator are not synchronized in frequency
Chapter 8 Communication Systems ② Sinusoidal carrier Communication LPF Channel oslo t+0 bos(o,t+0 Transmitter Receiver Modulation Synchronous Demodulation 1. Suppose the modulator and demodulator are not synchronized in phase. 2. Suppose the modulator and demodulator are not synchronized in frequency. 6
6 Chapter 8 Communication Systems ② Sinusoidal Carrier ( ) c c cos t + x(t) y(t) Communication Channel Transmitter Modulation Receiver Synchronous Demodulation LPF x(t) w(t) cos( d t + ) 1. Suppose the modulator and demodulator are not synchronized in phase. 2. Suppose the modulator and demodulator are not synchronized in frequency
Chapter 8 Communication Systems 583 frequency- Division multiplexing(频分复用) X1() I coSopt x1 y BPF 00 COS O2L O X2(o) V2 BPF M O M cOS a,t o x, go BPF TOM O yGj ● 0 7
7 §8.3 Frequency-Division Multiplexing（频分复用） Chapter 8 Communication Systems t 1 cos x (t) 1 t 2 cos x (t) 2 y (t) 1 BPF 1 y (t) 2 BPF 2 t n cos x (t) n y (t) n BPF y(t) n X (j) 1 − M 0 M − M 0 M X (j) 2 − M 0 M X ( j) n −2 −1 0 1 2 Y(j) −n n
Chapter 8 Communication Systems Quadrature Multiplexing(正交多路复用) coso t cos o t X y LPF r()communication Channel LPF f sin o t sin o t y()=x() y2(=x2() 8
8 Chapter 8 Communication Systems Quadrature Multiplexing（正交多路复用） t c cos x (t) 1 t c sin x (t) 2 r(t) t c sin t c cos LPF LPF y (t) 1 y (t) 2 M M Communication Channel r(t) w (t) 1 w (t) 2 y (t) x (t) 1 = 1 y (t) x (t) 2 = 2
Chapter 8 Communication Systems 58.4 Single-Sideband Sinusoidal Amplitude Modulation (单边带) Xlo x coso t 0 M Yo Upper Lower Del sideband sideband sideband 0 20 2 M M Double sideband Modulation ( DsB
9 Chapter 8 Communication Systems §8.4 Single-Sideband Sinusoidal Amplitude Modulation （单边带） − M 0 X(j) M t c cos x(t) y(t) −c 0 Y(j) c 2 M 2 M Upper sideband Upper sideband Lower sideband Double Sideband Modulation (DSB)
Chapter 8 Communication Systems Retain the upper sideband pper pper sideband sideband 0 M Retain the lower sideband Lower sideband 0 M Single sideband Modulation(SSB)
10 Chapter 8 Communication Systems Retain the upper sideband −c 0 c M Upper sideband Upper sideband M −c 0 c Lower sideband M M Retain the lower sideband Single Sideband Modulation (SSB)