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PCM(脉冲编码调制)介绍及PCM编码的原理---PCM量化13折线.pdf
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PCM(脉冲编码调制)介绍及PCM编码的原理---PCM量化13折线.pdf
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I
PCM(脉冲编码调制)介绍及 PCM编码的原理
摘 要
在数字通信信道中传输的信号是数字信号, 数字传输随着微电子技术和计
算机技术的发展,其优越性日益明显,优点是抗干扰强、失真小、传输特性稳
定、远距离中继噪声不积累、还可以有效编码、译码和保密编码来提高通信系
统的有效性,可靠性和保密性。另外,还可以存储,时间标度变换,复杂计算
处理等。
而模拟信号数字化属信源编码范围, 当然信源编码还包括并 / 串转换、加密
和数据压缩。这里重点讨论模拟信号数字化的基本方法——脉冲编码调制,而
模拟信号数字化的过程(得到数字信号)一般分三步:抽样、量化和编码。
本文讲述了 PCM(脉冲编码调制)的简单介绍,以及 PCM编码的原理,并分
别对 PCM的各个过程, 如基带抽样、 带通抽样、 13 折线量化、 PCM编码以及 PCM
译码进行了详细的论述, 并对各过程在 MATLAB7.0上进行仿真, 通过仿真结果,
对语音信号的均匀量化以及非均匀量化进行比较,我们得出非均匀量化教均匀
量化更加有优势。
关键词:脉冲编码调制 抽样 非均匀量化 编码 译码
II
Abstract
In the digital communication channel signal is digital signal transmission, digital
transmission with the microelectronics and computer technology, its advantages
become increasingly evident, the advantage of strong anti-interference, distortion,
transmission characteristics of stable, long-distance relay is not the accumulation of
noise Can also be effective encoding, decoding and security codes to improve the
effectiveness of communications systems, reliability and confidentiality.
Digitized analog signal range of source coding is, of course, also include the
source code and / serial conversion, encryption and data compression. This focus on
the simulation of the basic methods of digital signals - pulse code modulation, while
the analog signal the digital process (to get digital signals) generally three steps:
sampling, quantization and coding.
This paper describes the PCM (pulse code modulation) in a brief introduction, and
the PCM coding theory, and were all on the PCM process, such as baseband
sampling, bandpass sampling, 13 line quantization, PCM encoding and decoding
PCM a detailed Are discussed and the process is simulated on MATLAB7.0, the
simulation results, the uniformity of the speech signal quantification and comparison
of non-uniform quantization, we have come to teach non-uniform quantization
advantage of more than uniform quantization
Keywords : Pulse Code Modulation Sampling Non-uniform quantization
Coding Decoding
III
目录
1 前 言 ······················································································································1
2 PCM原理 ·················································································································2
2.1 引言 ···············································································································2
2.2 抽样 (Sampling) ···························································································3
2.2.1. 低通模拟信号的抽样定理 ······························································3
2.2.2 抽样定理 ······························································································4
2.2.3. 带通模拟信号的抽样定理 ·································································7
2.3 量化( Quantizing ) ···················································································8
2.3.1 量化原理 ······························································································8
2.3.2 均匀量化 ·····························································································10
2.3.3 非均匀量化 ························································································ 11
2.4 编码( Coding) ·························································································18
2.5 译码 ·············································································································24
2.6 PCM 处理过程的其他步骤 ········································································26
2.7 PCM 系统中噪声的影响 ············································································27
3 算例分析 ··············································································································29
3.1 无噪声干扰时 PCM编码 ·············································································30
3.2 噪声干扰下的 PCM编码 ·············································································36
结论 ····························································································································42
致谢 ····························································································································43
参考文献 ····················································································································44
附录 ····························································································································45
1
1 前 言
数字通信系统中信道中传输的是数字信号,数字传输随着微电子技术和计
算机技术的发展,其优越性日益明显,优点是抗干扰强、失真小、传输特性稳
定、远距离中继噪声不积累、还可以有效编码、译码和保密编码来提高通信系
统的有效性,可靠性和保密性。另外,还可以存储,时间标度变换,复杂计算
处理等。
但自然界中,有些信源是以模拟形式出现的,如话音、图像等。因此在进
行数字通信往往需先对信号(模拟的)数字化。模拟信号数字化属信源编码范
围,当然信源编码还包括并 / 串转换、 加密和数据压缩。 这里重点讨论模拟信号
数字化的基本方法——脉冲编码调制,而模拟信号数字化的过程(得到数字信
号)一般分三步:抽样、量化和编码。但是这三个步骤是怎样的完成的呢?我
们知道电话语音信号是用脉冲编码体制技术进行编码传输,但是究竟每一步怎
样语音信号都有怎样的改变呢?本文将进行详细讲述
本论文主要对模拟信号数字化传输过程进行分析仿真, 包括脉码调制(Pulse
Code Modulation)的原理过程,算例分析等,经过信号调制原理的分析,并在
MATLAB7.0 编译环境下编写相应程序平台,便于实验的直观分析和数据分析,
最后我们得出在相同量化电平级数 M 下,非均匀量化输出信噪比较均匀量化要
小,对于语音信号来说,小信号的出现概率大于大信号的出现概率,非均匀量
化的优势将更加明显的结论。通过对脉冲编码调制的分析加深了对语音信号经
脉冲编码调制处理过程的理解,锻炼了学生科研与写作能力,为通信原理课程
建设提供素材,并为教学提供仿真平台。
由于时间的仓促以及本人的水平有限,文中难免有不足之处,恳请各位老
师指正,在此不慎感激。
2
2 PCM 原理
2.1 引言
现在的数字传输系统都是采用脉码调制( Pulse Code Modulation ) 体制。
将模拟语音信号变换为数字信号的编码方式, 特别是对于音频信号。 PCM 对信
号每秒钟取样 8000 次;每次取样为 8 个位,总共 64kbps,取样等级的编码
有二种标准。 PCM 有两个标准即 E1 和 T1。我国采用的是欧洲的 E1 标准。 T1
的速率是 1.544Mbit/s,E1 的速率是 2.048Mbit/s。
脉冲编码调制主要经过 3 个过程:抽样、量化和编码。抽样过程将连续
时间模拟信号变为离散时间、连续幅度的抽样信号,量化过程将抽样信号变为
离散时间、离散幅度的数字信号,编码过程将量化后的信号编码成为一个二进
制码组输出。下面将 PCM 脉冲编码调制原理作着重介绍,对这里不再赘述。
所谓脉冲编码调制,就是将模拟信号抽样量化,然后将已量化值变换成代
码。下面将用一个 PCM 系统的原理框图简要介绍,原理框图如图 2.1 所示。
图 2.1 PCM 原理方框图
抽 样
保 持
量化器 编码器
信
道
译码器
低 通
滤 波 器
PCM 信号
输出
干扰
PCM信号
输入
模 拟 信 号
输出
冲激脉冲
模拟信号
输入
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