Bilingual Course Network Communications 网络通信 ( For Master Students in the Department of Electronic Engineering) Chapter 5 Signal Encoding Instructor: Dr Tianshuang Qiu School of the Electronic and Information Engineering Fall of 2004
1 Bilingual Course Network Communications 网络通信 (For Master Students in the Department of Electronic Engineering) Chapter 5 Signal Encoding Instructor: Dr. Tianshuang Qiu School of the Electronic and Information Engineering Fall of 2004
Data Encoding Digital data, digital signal: In general, the equipment for encoding digital data into a digital signal is less complex and less expensive than digital-to-analog modulation equipment Analog data, digital signal: conversion of analog data to digital form permits the use of modern digital transmission and switching equipment. The advantages of the digital approach were outlined in Section 3. 2 Digital data, analog signal: Some transmission media, such as optical fiber and unguided media, will only propagate analog signals Analog data, digital signal: Analog data in electric form can be transmitted as baseband signals easily and cheaply. This is done with voice transmission over voice-grade lines. One common use of modulation is to shift the bandwidth of a baseband signal to another portion of the spectrum. In this way multiple signals each at a different position on the spectrum, can share the same transmission medium. This is know as frequency-division multiplexing 2
2 Data Encoding Digital data, digital signal: In general, the equipment for encoding digital data into a digital signal is less complex and less expensive than digital-to-analog modulation equipment. Analog data, digital signal: conversion of analog data to digital form permits the use of modern digital transmission and switching equipment. The advantages of the digital approach were outlined in Section 3.2. Digital data, analog signal: Some transmission media, such as optical fiber and unguided media,will only propagate analog signals. Analog data, digital signal: Analog data in electric form can be transmitted as baseband signals easily and cheaply. This is done with voice transmission over voice-grade lines. One common use of modulation is to shift the bandwidth of a baseband signal to another portion of the spectrum. In this way multiple signals, each at a different position on the spectrum, can share the same transmission medium. This is know as frequency-division multiplexing
85-1 Digital Data, Digital Signal 0:1:0:01:1:0:0:0:1:1 NRZ-L NRZI Bipolar-AMI Pseudoternary Manchester lUyuN Differential Manchester Figure 5.2 Digital Signal Encoding Formats 3
3 §5-1 Digital Data, Digital Signal
1.几种编码形式 (1) Non Return to Zero(nrz 最简单; 在一个bit周期内电平横定 正负跳变,不回0 0一由高电平表示,1—由低电平表示 优点:易于实现,有效利用带宽; 缺点:有直流成分,缺乏同步能力(若一串1或一串0,则无法同 步)
4 1. 几种编码形式 （1）Non Return to Zero (NRZ) • 最简单； • 在一个bit周期内电平横定； • 正负跳变，不回0； • 0—由高电平表示，1—由低电平表示； • 优点：易于实现，有效利用带宽； • 缺点：有直流成分，缺乏同步能力（若一串1或一串0，则无法同 步）
(2) Nonreturn to Zero inverted(NRZⅠ不归零1制 0—在间隔的起始位置无跳变 1—在间隔的起始位置有跳变 (其他特点同NR (3) Bipolar AMI( Alternate mark inversion,交替信号反转) 0一没有信号 1—正/负电平 优点:很长的串1,不会失去同步; 信号1在正负电平之间跳变,无直流分量; 信号的带宽比较窄 脉冲交替,有利于差错检测 (4) Pseudoternary(伪三进制) ·0—正电平或负电平; 1—没有信号
5 （2）Nonreturn to Zero Inverted (NRZI, 不归零1制) • 0—在间隔的起始位置无跳变 • 1—在间隔的起始位置有跳变 （其他特点同NRZ） （3）Bipolar AMI (Alternate mark inversion, 交替信号反转) • 0—没有信号； • 1—正/负电平 • 优点：很长的串1，不会失去同步； 信号1在正负电平之间跳变，无直流分量； 信号的带宽比较窄； 脉冲交替，有利于差错检测 （4）Pseudoternary（伪三进制） • 0—正电平或负电平； • 1—没有信号