多种正交幅度调制QAM误码率仿真及星座图的优化

文档编号:TX364  文档字数:10967,页数:43

摘要

 在通信技术日益发达的今天，各种各样的信息传输技术也相继出现，如脉冲幅度调制（PAM）、脉冲编码调制（PCM）、相移键控（PSK）、差分相移键控（DPSK）、频移键控（FSK）、幅移键控（ASK）、正交幅度调制（QAM）等调制解调技术。各种技术都有它的优缺点和适合它的工作环境。由于每种技术都并不完美，总有改进的空间，所以对一些技术进行适当的改善，增加传输准确率，抑或提高传输效率，又或者降低传输成本等等，都是值得我们去研究和讨论的。
 QAM依靠其高效的带宽效率成为一种被广泛使用的调制解调技术。另一方面，它的误差性能比二相相移键控（BPSK）和四相相移键控（QPSK）更糟。QAM的每个星座有一种最佳的星座图分布和最低的误符号率。常用的QAM，如QPSK、矩形16QAM，并不是最佳星座图，但易于硬件的实现。
 本文介绍了QAM的概念、产生、优点和缺点，以及在高斯白噪声中的误符号率性能。我们通过MATLAB仿真获得不同的16QAM误符号率性能，并且找到最佳的16QAM星座图。常规的格雷编码不适合最佳星座图，因此，我们可以再一次用MATLAB仿真获得和比较不同映射的误比特率性能。
 本文的另一个贡献是，一个标准化的仿真程序可以输入任意的16QAM星座图来对误符号率进行仿真。同时，我们也建立了一个友好的MATLAB图形用户界面（GUI），从而使之容易输入星座图测试坐标，并且方便地比较不同星座图的仿真结果。

关键词：16QAM，MATLAB，误符号率，误比特率，最佳星座图

ABSTRACT

 In today's increasingly advancing communication technologies, a variety of modulation techniques have been used, such as Pulse Amplitude Modulation(PAM), Pulse Code Modulation(PCM), Phase-Shift Keying(PSK), Differential Phase-Shift Keying(DPSK), Frequency-Shift Keying(FSK), Amplitude-Shift Keying(ASK), Quadrature Amplitude Modulation (QAM). Each modulation technique has its advantages and disadvantages and its designed working environment. As each technique is not perfect, there is always room to improve for every technology, for example, to improve error performance, or increase bandwidth efficiency, or reduce the transmission cost.
 QAM is a widely used modulation and demodulation technique due to its high bandwidth efficiency. On the other hand, its error performance is worse than binary PSK (BPSK) and quadrature PSK (QPSK). Each constellation size has an optimal constellation design with the lowest symbol error rate (SER).  QAM constellations often used in practice, e.g. QPSK, 16 square QAM, are usually not optimal, due to implementation complications. 
 This thesis introduces the concept of QAM, system diagram, its advantages and disadvantages, and SER performance analysis over additive white Gaussian channels (AWGN). We obtain SER performance of various 16QAM constellations via MATLAB simulation and find the optimal one. Conventional Gray coding is not possible for the optimal constellation. Therefore, we again used MATLAB simulation to obtain and compare bit error rate (BER) of various mappings.
 Another contribution of this thesis is that we standardized the simulation program such that an arbitrary constellation of 16QAM can be inputted for SER/BER performance simulation. We also constructed a user-friendly MATLAB graphics user interface (GUI) that allows for easy input of trial constellation coordinates, and convenient comparison of simulation results.
Keywords: 16QAM，MATLAB，SER，BER，Optimal constellation.
目录

摘要 I
ABSTRACT II
第1章 引言 1
 1.1 背景 1
 1.2 研究内容 2
第2章 正交幅度调制QAM 3
 2.1 QAM的定义 3
 2.2 QAM的调制 4
 2.3 QAM的解调与检测 5
 2.4 AWGN信道中的QAM差错概率 7
 2.5 QAM的优缺点 9
 2.6 AWGN信道 9
第3章 最佳16QAM星座图 10
 3.1 渐近表达式的错误率 10
 3.2 最佳信号星座的菱形变换 11
 3.3 16QAM最佳星座图 12
 3.4 16QAM最佳星座图的误比特率的编码优化 14
第4章 16QAM的MATLAB误码率仿真 16
 4.1 矩形16QAM的误码率和误比特率仿真 16
 4.2 不同星座图的16QAM误码率比较 19
 4.3 最佳16QAM星座图误比特率的编码比较 20
 4.4 图形用户界面(GUI)设计 22
致谢 24
参考文献 25
附录 源代码 26

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