chapter5-modulation.ppt

munications
Chapter 5: Modulation Techniques for Mobile Radio
Block Diagram of munication Systems
Format
X
M
T
R
C
V
Source
encode
Encrypt
Channel
encode
Multi-
plex
Pulse
modulate
Bandpass
modulate
Frequency
spread
Multiple
access
Format
Source
decode
decrypt
Channel
decode
Demulti-
plex
detect
Demod-
Ulate
&sample
Frequency
spread
Multiple
access
optional
Essential
To other destinations
Channel symbols
Message symbols
information sink
information source
Message symbols
Channel symbols
From other sources
C
H
A
N
N
E
L
Channel impulse response
Digital bandpass waveform
Digital baseband waveform
Synch-
ronization
Bit
stream
Digital input
Digital output
1,0,…
gi(t)
基本术语
二进制序列(binary sequence): sequence of {1, 0} to describe information source
位(Bit) 符号(symbol): a symbol represents k bits (M=2k)
符号集(Symbol alphabet): s0,s1,…,sM-1 (alphabet size M)
符号流(symbol stream): sequence of symbols selected from the alphabet
数据率(Data rate )
Bit rate Rb in bits/sec (bps).
Symbol rate Rs in symbols/sec (sps)
Bit interval Tb: duration of a bit (sec/bit)
Symbol interval Ts: duration of a symbol (sec/symbol)
重要的关系
Example: a binary sequence is obtained by sampling a voice signal with 8-bit A/D and sampling rate of 8kHz.
What are bit rate and bit interval?
If QPSK is used for transmission (each symbol represent two bits), what are M, k? What are symbol rate and symbol interval?
Illustration and example
调制的概念
调制的定义
将信源编码转变成“适合”“传输”的形式;
目标
尽可能好的质量,占用尽可能少的带宽;
调制分类
按照波形
模拟调制
数字调制
按照频率
基带调制(baseband)
带通调制(bandpass)
带通调制作用(不仅仅用在无线系统)
天线:low-frequency to high frequency;
频分复用: FD;
模拟基带“调制”
模拟信号 to municating a signal in its original form for a given medium )
Eg. POT
数字基带调制(line coding)
二进制数字 to 波形{ Communicating a signal ponents down to DC (or almost DC)}
PCM waveform: rectangular wave without pulse shaping
Baseband waveform: smooth wave with limited bandwidth after pulse shaping
主要类型
NRZ(不归零波形)
RZ(归零波形)
相位编码
多电平二进制
其他类型的调制
PAM
PCM
PWM
基带调制