[工学]通信原理5章复习.ppt

signal processing carrier circuits Transmission Medium (channel) carrier circuits signal processing output input Modulating signal Modulated signal Baseband signal Bandpass signal Baseband signal Bandpass signal Chapter5 AM,FM,and Digital Modulation System Date1 modulated bandpass signal: The spectrum of : and the PSD is: Date2 u 要求： 关于模拟调制 1. 掌握 AM、DSB-SC、SSB调制原理和解调方法，会计 算各种已调信号的调制效率、AM信号的调制百分比、平 均功率、峰值包络功率、功率谱、带宽。了解AM、 DSB -SC信号的波形特点； 2. 了解FM、PM的各种基本概念，了解FM、PM两种调 制之间的关系，会估算FM、PM信号的带宽（掌握卡森公 式）。 3. 了解频分复用的基本概念。 Date3 关于数字调制 1. 掌握 2ASK、2PSK、2FSK的调制原理和解调方法 ，会计算各种已调信号的功率谱、带宽（包括无ISI 系统）。会画2ASK、2PSK、2FSK信号波形； 2. 了解 MQAM、QPSK、 MPSK的调制原理和解调方 法，了解 OQPSK 、/4QPSK、MSK 的调制原理，会 计算各种已调信号(MQAM、QPSK、 MPSK、 OQPSK、/4QPSK)的功率谱、带宽（包括无ISI系统 ）。了解各种调制的星座图。会画 Type I MSK、 Type MSK 同相路和正交路基带波形 x(t) 、y(t) 。 Date4 5.1 Amplitude Modulation Upper sideband Lower sideband Date5 一般： Complete amplitude modulation an envelope detector can be used to demodulating the modulated signal Date6 The percentage of modulation on an AM * the percentage of positive modulation * the overall modulation percentage * the percentage of negative modulation 调制百分比影响功 率分配 Date7 The power allocation of AM signal and modulation efficiency The power allocation of AM signal The normalized average power of the AM signal: Often: Date8 Modulation efficiency The normalized PEP of the AM signal: Date9 Characteristic of AM signal: l Envelope detector is used to detecting the AM signal. l The power efficiency of the AM signal is lower. l The bandwidth of the AM signal is two times that of m(t). Date10 5.3 Double-Sideband Suppressed Carrier (DSB-SC) The percentage of modulation: It is infinite because of no carrier. The modulation efficiency of DSB-SC is Date11 spctrum Date12 载波反相点 waveform: Date13 Modulation Demodulation The transmitter and receiver LPF Date14 l The percentage of modulation: It is infinite because of no carrier. Characteristic of DSB signal: Date15 5.5 Asymmetric Sideband Signals 1.Single sideband signal (SSB) (1) Representation The complex envelope of a SSB is: The single sideband signal: Date16 Date17 The normalized PEP (2) The power The normalized average power Date18 (3) The receiver a product detector: LPF Date19 Date20 （1）Phase Modulation (PM) 相位偏移正比于调制信号 5.6 Phase modulation and Frequency modulation Date21 （2）Frequency Modulation (FM) 相位偏移正比于调制信号 的积分。 Instantaneous frequency deviation: 频率偏移正比于调制信号 。 Date22 (a) PM:(b) FM: Date23 （3）Bandwidth of the angle-modulated signal B - the bandwidth of For PM: , for FM: Carsons rule Date24 （4）The spectral of PM or FM with Sinuoidal Modulation 正频 Date25 角调信号的离散载波功率： 角调信号的各次边频功率： Summary: 不同时，载波功率和各边频功率的分配关系也发生变化 。 已调后： ，载波功率 ，转变为各边频 功率，而总功率不变。 角调信号的总功率： Date26 Generation of PM using a FM modulator （5）The convert between FM and PM Generation of FM using a PM modulator Date27 Date28 5.7 Frequency-Division Multiplexing(FDM) 1.Definition FDM is a technique for transmitting multiple messages simultaneously over a wideband channel. Date29 on-off keying (OOK) Binary phase- shift keying (BPSK) Frequency- shift keying (FSK). 5.9 Binary Modulated Bandpass Signaling Date30 1. 2ASK signal (2 Amplitude shift keying) (1) Modulation Unipolar NRZ The complex envelope: Date31 The PSD and bandwidth of the OOK complex envelope: By Eq. (3.39b),we get: The PSD of g(t) is The PSD of s(t) is Date32 Date33 When we make no ISI filtering (如 作升余弦谱滤波） Spectral Efficiency: Date34 (2) Demodulation Envelope Detector Envelope Sample And judge Coherent Detector LPF Sample And judge Optimum receiver-Matched Filter receiver Date35 2. BPSK (2PSK) (Phase-Shift Keying) (1) Modulation method 1th Modulator: Modulator Polar NRZ Date36 信号矢量图 （星座图）： 参考相位（未调载波初相） Date37 (2) Modulation method 2th 星座图： 调制： Polar NRZ Date38 Demodulator: Date39 (3).The PSD of the BPSK The PSD of s(t) is The PSD of g(t) is By Eq. (3.39b),we get: Date40 Date41 When we make no ISI filtering (如 作升余弦谱滤波 ） Date42 4、2FSK (Frequency-Shift Keying) (1) Discontinuous-phase FSK Producer of FSK Oscillator f1 Oscillator f2 gate gate Inverse Unipolar NRZ + FSK Discontinuous-phase FSK Continuous-phase FSK Classify: Date43 Date44 So FSK signal can be represented as: 可以看成是两个不同载频 的 ASK 之和。 Frequency field Where: B - bandwidth of m(t) Date45 When m(t) is rectangular: Date46 When we make no ISI filtering (如 作升余弦谱滤波） 峰峰频偏 Date47 (2) Continuous-phase FSK Producer of FSK Frequency Modulator fc Date48 The representation The continuous phase Date49 B - bandwidth of baseband signal m(t) The frequency field Carsons rule: When m(t) is square-wave: Date50 u在描述FSK信号特性时，常用到两个参数：载波频率fc和 数字调制指数h。 Date51 (3) Demodulation for FSK noncoherent detection a. 适合于频差较大的场合 code BPF(f1) BPF(f2) 整流 整流 LPF LPF 抽样判决 Envelope detector Envelope detector Date52 b. Frequency detector Date53 coherent detection BPF BPF LPF LPF 抽样判决 频差较大时适合 频差较小时，若 正交，则 LPF换成积分器可实现最佳接收。 Date54 (4)波形相关系数 Discuss: the relation of two carrier of FSK 波形相关系数: Date55 时 , 称 在0,Tb内正交 Date56 (1) For continuous-phase FSK Date57 (2) For discontinuous-phase FSK To satisfy the (3): 是满足正交的最小值。 所以，相位不连续时，FSK带宽略大。 Date58 5.10 Multilevel Modulated Bandpass Signaling These multilevel modulated bandpass signalings are usually used in practice. QAM、QPSK、OQPSK、/4QPSK 、MSK、GMSK 2/M converter Modulator Binary signal M=2l level Modulated signal Date59 1.MPSK and QPSK (1) MPSK Date60 信号星座图： Date61 (2) QPSK (4PSK ) 最大相位跳变为 QPSK modulator 2bit 串/并变换 binary 单/双极性 单/双极性 可引入无ISI滤波器 Date62 QPSK demodulator LPF LPF Decider Decider sampling sampling binary 并/串 可引入无ISI滤波器 Date63 2. QAM 对于MASK，矢量端点在一条轴上分布； 对于MPSK，矢量端点在一个圆周上分布 ；对于QAM，矢量端点在整个信号平面上 分布； Date64 QAM modulator 2bit 串/并变换 binary 2/L电平变换 2/L电平变换 可引入无ISI滤波器 Date65 10000111 10 00 01 11 01111111 00111011 Date66 The general QAM signal is its complex envelope is h1(t) - the pulse shape used for each symbol Date67 QAM demodulator LPF LPF Decider (L-1)个门限 sampling sampling binary 并/串 可引入无ISI滤波器 Decider (L-1)个门限 Date68 When M=4 , 4QAM=QPSK offset QAM (OQAM) The timing between the x(t) and y(t) components is offset by Ts/2, that is: Date69 3.OQPSK and /4QPSK (1).OQPSK (Offset QPSK) OQPSK is identical to offset QAM when M=4. 最大相位调变为 Date70 (2) /4QPSK It is generated by alternating between two QPSK constellations that are rotated by /4 with respect to each other. 如： 01 11 00 10 最大相位调变为 Date71 Example: 10 01 10 10 01 11 10 11 01 01 10 10 Date72 q Relationship between QPSK ,/4 QPSKand OQPSK 4QAMQPSK Delay Alternating 注：若基带用矩形波传时，它们是恒包络调制，但已调信 号谱太宽； Date73 若基带用升余弦谱波限带时，已调信号会有AM分量。经分 析：相位跳变越大，则AM分量越大。这使得限带后的信号 不能用效率高的非线性C类放大器放大，只能用A、B类线性 放大器。 Type of modulation Maximum phase shift AM big smallsmallest Date74 Date75 4. The PSD of MQAM、QPSK、OQPSK、/4QPSK （1） The PSD of MQAM 2bit 串/并变换 binary 2/L电平变换 2/L电平变换 当M4时，L2 MPSK与MQAM信号在相同信号点数时功率谱相同 ，带宽均为基带信号带宽的两倍。 Date76 若正交路、同相路基带信号用矩形波（polar NRZ)， 则 基带信号带宽为： Date77 若正交路、同相路基带信号用升余弦谱波 Date78 （2） The PSD of 4QAM（QPSK）、OQPSK、 /4QPSK 若正交路、同相路基带信号用矩形波（polar NRZ)， 则 基带信号带宽为： Date79 Date80 若正交路、同相路基带信号用升余弦谱波 Date81 5.11 MSK ( Minimum-Shift Keying ) Properties of MSK * continuous -phase 2FSK * constant envelope * modulation index being