MSK调制解调系统的设计
[摘要] 最小频移键控（MSK）是恒定包络调制技术，它具有相位连续、频带利用率高的特点，是在无线通信
领域中很有吸引力的数字调制方式，目前在短波、微波和卫星通信中均被采用。本文研究了最小频移键控系统调制与解调的工作原理，并给出了基于MATLAB软件环境下的程序仿真及simulink下系统的模块搭建实现两种方式的实现。运用m语言进行仿真，主要是依照MSK系统的工作原理绘制出流程图，最后写出程序进行仿真，并给出每一步骤的仿真结果图形。运用simulink进行系统的模块搭建，是将系统分为调制与解调两个子模块，再将这两个子模块连接成整体的MSK系统模块进行仿真。最后给出全系统的仿真运行结果及其分析研究结果。
[关键字]MSK； Matlab；Simulink；调制解调
Simulation of MSK Modulation and Demodulation System
[Abstract] Minimum Shift Keying (MSK) is a constant envelope modulation techniques, it has a continuous phase,
high bandwidth efficiency characteristics, is very attractive in the field of wireless communications, digital modulation, shortwave, microwave and satellite communicationsmedium were used. In this paper, the working principle of minimum shift keying modulation and demodulation, and gives the realization of program simulation and simulink system module in the MATLAB software environment to build in two ways. M language simulation, the main draw a flow chart in accordance with the MSK system works, and finally write the program simulation, and gives each step of the simulation results graphics. Use simulink module of the system construction, the two sub-modules of the system is divided into modulation and demodulation, and then two sub-modules connected into the overall MSK system module for simulation. Finally, the simulation run of the system-wide results and their analysis results.
[Key words]MSK; Matlab ;Simulink; Modulation and Demodulation
目录
引言 ·················································································· 1 1 方案的论证与选择 ····························································· 3
1.1 基于SystemView的设计 ······················································· 3 1.2 基于Matlab的设计 ····························································· 3 1.3 基于FPGA的设计 ································································ 3 1.4 方案选择 ·········································································· 4
2 MSK信号调制解调原理 ························································ 5
2.1 MSK的特点 ········································································ 5 2.2 MSK的调制原理 ·································································· 5 2.3 MSK的解调原理 ································································ 10 2.4 MSK的性能分析 ································································· 11
3 基于Matlab的MSK调制解调系统的设计 ······························· 13
3.1 Matlab中的m语言和Simulink简介 ····································· 13 3.2 运用m语言设计MSK调制解调系统 ······································· 14 3.2.1运用m语言设计的流程图 ·············································· 14 3.2.2测试结果及分析 ·························································· 15 3.3 运用Simulink设计MSK调制解调系统 ··································· 18 3.3.1 Simulink MSK调制模块设计 ·········································· 18 3.3.2 Simulink MSK解调模块设计 ·········································· 19 3.3.3 测试波形分析 ····························································· 21
结束语 ············································································· 25 致谢 ················································································ 26 参考文献 ·········································································· 27 附录A 英文文献原文 ·························································· 28
附录B 英文文献译文 ·························································· 38 附录C m程序 ···································································· 49
引言
随着经济的发展，人们对通信系统的需求越来越来高。通信系统也由原来的单一对点传输。逐渐发展成大容量高速的网络通信体制。通信系统的增多，通信的频率资源就显得相对紧张，如何能在现有的频率资源的条件下实现大容量的通信是现在通信考虑的主要问题。根据通信系统的基点，人们在实践中相继研发出很多种通信的调制方式，主要有：振幅键控(ASK)、移频键控(FSK)、移相键控(PSK)等。从频谱的利用率上人们又研究出MSK、GMSK等频谱利用率较高的调制方式。 在数字通信、网络、视频和图像处理领域，MSK已经成为高性能数字信号处理系统的关键元件。MSK是一种在无线移动通信中很有吸引力的数字调制方式，它具有以下两种主要的特点：
1．信号能量的99.5%被限制在数据传输速率的1.5倍的带宽内。谱密度随频率（远离信号带宽中心）倒数的四次幂而下降，而通常的离散相位FSK信号的谱密度却随频率倒数的平方下降。因此，MSK信号在带外产生的干扰非常小。这正是限带工作情况下所希望有的宝贵特点。
2．信号包络是恒定的，系统可以使用廉价高效的非线性器件。 无线通信技术的迅猛发展对数据传输速率、传输效率和频带利用率提出了更高的要求。选择高效可行的调制解调手段,对提高信号的有效性和可靠性起着至关重要的作用。因此具有频带利用率高,在相同误比特率下所需的信噪比比较低,电路结构比较简的MSK技术已经广泛应用到现代通信领域。
调制是移动通信系统中提高通信质量的一项关键技术，调制是为了使信号特性与信道特性相匹配。现代移动通信系统大多数使用的是数字调制技术，这主要是由于数字通信网建网灵活，并且数字加密技术便于集成化。因此，通信系统都在由模拟方式向数字方式转换，这也是移动通信的发展趋势。但是，一般的数字调制技术，如振幅键控（ASK）、频移键控（FSK）和相移键控（PSK）等都无法满足移动通信的要求。因此，寻找性能优越的高效调制方式以适应现代移动通信的要求，一直是重要的研究课题。MSK调制的出现，是为了获取更好的通信质量。
当信道中存在非线性的问题和带宽限制时，幅度变化的数字信号通过信道会使己滤除的带外频率分量恢复，发生频谱扩展现象，同时还要满足频率资源限制的要求。因此，对己调信号有两点要求，一是要求包络恒定；二是具有最小功率谱占用率。因此，现代数字调制技术的发展方向是最小功率谱占有率的恒包络数字调制技术。现代数字调制技术的关键在于相位变化的连续性，从而减少频率占用。近年来新发展起来的技术主要分两大类：一是连续相位调制技术（CPFSK），在码元转换期间无相位突变，如MSK，GMSK等；二是相关相移键控技术（COR－PSK），利用部分响应技术，对传输数据先进行相位编码，再进行调相（或调频）。 MSK是Doelz和Heald在他们的一项专利中提出的一种信号的调制方式。1972年，DeBuda认为MSK就是一种特殊的CPFSK调制方式，经过一段时间的发展，MSK被认为是正弦加权的OQPSK的形式。1977年，Amoroso and Kivett通过一系列的变化把MSK简化成了SMSK。目前，MSK在实际的通信系统中已经得到了广泛的应用。例如，SMSK已应用在美国航空和宇宙航行局的高级通信卫星上，GMSK已经应用于欧洲GSM通信系统中。对MSK的功率谱进行仿真,从结果看,MSK调制方式并不适用于数字移动通信,需对其进行改进.由此,产生了高斯最小频移键控(GMSK)调制方式,从仿真结果来看,其性能大大改善.目前,GMSK调制方式广泛用于GSM,对不同参数的GMSK调制的功率谱进行仿真,可得到一种较好的GMSK调制方式,对GMSK在实际中的应用进行了有益的理论指导。
最小移频键控(MSK)是移频键控(FSK)的一种改进型。在FSK方式中，相邻码元的频率不变或者跳变一个固定值。 在两个相邻的频率跳变的码元之间，其相位通常是不连续的。MSK是对FSK信号作某种改进，使其相位始终保持连续不变的一种调制信号。MSK调制指数为0．5，包络恒定、相位连续、频带利用率高、功率谱紧凑，且频谱滚降快，产生带外干扰小．抗干扰性能好，因此在军用和民用通信领域中均获得了广泛的应用。用数字基带信号去控制可变分频器的分频比来改变输出载波频率，使输出信号频率发生变化的同时，相位保持连续，从而实现MSK调制。
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