毕业设计（论文）-CDMA系统的研究与MATLAB仿真.doc

CDMA系统的研究与MATLAB仿真
摘要
CDMA(Code Division Multiple Access)是在扩频通信的基础上发展起来的。所谓扩频,是将原信号频谱扩展到宽带中进行传输的一种技术。它主要利用相互正交(或尽可能正交)的不同随机码区分用户,实现多用户同时使用同一频率接入系统和网络。经过几种网络的实现和发展,CDMA已经逐渐成熟起来。我国的CDMA发展十分迅速,网络构架已初具规模。预计在将来,CDMA将与GSM一样,在整个通信业起到举足轻重的作用。仿真是一个系统应用于实际生活前的模拟,能有效的发现问题、纠正问题,而MATLAB是最具影响力、最有活力的软件之一,在科学运算、自动控制、通信仿真等领域有着广泛地应用。本课题利用MATLAB对DS-CDMA系统进行仿真。
在研究DS-CDMA系统理论的基础上,利用SIMULINK对其进行仿真,根据系统功能和指标要求,对信道、扩频/解扩、QPSK(Quadrature Reference Phase Shift Keying,四相相移键控)调制/解调等模块进行了设计,并设置了相对应的参数,最后给出系统仿真的整个框图。
通过波形、频谱图、相位等结果,对系统进行了性能分析,并作了进一步改进与调试。仿真结果证明了整个设计系统的正确性。由频谱特性可以看出,信源信号的频谱被大大展宽,验证了扩频的实现;由误码率分析表明,系统对加性高斯噪声等具有一定的抗干扰能力等。可以看出,MATLAB在系统动态仿真中具有较大优越性和重要作用。

关键词:直扩系统;CDMA;PN扩频;QPSK调制解调;simulink仿真
CDMA system research and simulation by MATLAB
Abstract
CDMA (Code Division Multiple Access) is a branch technology which based on the spectrum-spread of the munication. The spectrum spread is a kind of technology that expands the original signal frequency spectrum to a wide band in the transmission. It discriminates different users mainly by the different mutual orthogonal (or as far as possible orthogonal) random code. It can realize munication which multi-users utilize the same frequency to connect to the system and work. CDMA e more and more mature through the developments of works. The development of CDMA is very quick in China nowadays. work configuration of CDMA is basically self-contained. CDMA will exert important functions munication field as GSM in the future, but the amalgamation of CDMA and GSM is another direction. The simulation is the base of a system before it is used in the life, through which we can find the problems and correct them. Matlab is one of the most popular and vigorous software massively applied in science operation, automatic control, science cartography and correspondence simulation.
In my design, after studying the DS-CDMA system theory, take the Matlab to simulate it, mainly containing the PN code wide frequency design, the QPSK(Quadrature Referenc