摘 要直接扩频序列调制是用速率很高的伪噪声码序列与信息码序列模二相加后(波形相乘）得带复合码序列，用复合码序列去制载波相位，从而获得直接扩频序列信号的。直接扩频通信具有低截获概率、抗干扰能力强以及易于实现码分多址等优点,在抗干扰通信及民用移动通信中都得到了广泛的应用。先阐述了扩频通信的基本原理、主要性能指标及其工作特点，然后根据香农定理在抗下扰理论，借助工具箱和仿真算法，建立了直接序列扩频通信系统仿真模型.通过分析无干扰时的误码率仿真曲线与理论计算值，证明了所建仿真模型的正确性。在 MATLAB 程序仿真部分，主要分为 6 大部分，分别为主函数，发送模块，接收模块，AWNG信道，Walsh 函数和差错计数器。通过主函数对各个子函数的调用，实现 4 个用户的随机数据的发送和接收,同时生成前 4 个用户在整个传输过程中的各种波形变化图,并对系统信噪比与误码率关系进行分析。扩频通信是通信的一个重要分支和信道通信系统的进展方向。扩频技术具有抗干扰能力强，保密性好,易于实现多址通信等优点，因此该技术越来越受到人们的重视,这也是选择本次课题讨论的原因所在。关键词：直接序列扩频信号，通信,MATLABABSTRACTDirect—sequence spread spectrum transmitters (DS—SS) use a periodical pseudo—random sequence （PN sequence) to modulate the baseband signal，and exploit the modulated signal to control the phase of carrier wave. Because DS signals show many advantages such as anti-jamming capability。 low probability of interception. multiple access capability and so on. direct sequence spread spectrum signals have been widely applied for secure communications and mobile communications known as Code Division Multiple Access System。This thesis expounds the basic principles of spread spectrum communication ， and then article mainly acts according to the Shannon theorem 。 with the aid of matlab toolbox. it has established the direct sequence spread spectrum communications system simulation model which does not have when the disturbance through the analysis corror rate simulation curve and theory...
