基于稀疏图的DS-CDMA系统设计

DS-CDMA是在扩频技术上发展起来的多址接入方式,但在用户接入数量过载时难以保证高质量的通信性能。基于此,提出了一种基于稀疏图的DS-CDMA系统。该系统以低密度二分图的形式来描述扩频码片和用户之间的关系,使得参与通信的每个用户只在少量码片上进行非零位扩频调制,最大程度地减少了用户间的相互干扰。借助图模型的相关理论,把适合于稀疏图的置信度传播算法应用于该系统,进行多用户检测,通过码片与用户之间的消息迭代来消除噪声和多址干扰带来的影响。结合计算机仿真,从不同的角度测试了系统的误码率等性能。理论分析与性能验证表明,稀疏图DS-CDMA在接入用户数量远远超过系统容量的情况下,依然具有优良的性能。

Design of DS-CDMA system based on sparse graph

DS-CDMA is a multiple access technology which is developed based on spread spectrum, but it is difficult for such system to attain satisfactory performance under overloading conditions. This paper presents a sparse DS-CDMA system. It is possible to represent the relationship between chips and users using a low density Tanner graph. By doing so, each user is only connected to limited non-zero chips, which can minimize the multiuser interference. According to graph theory, belief propagation algorithm, that is suitable to the case of low density graph, is adopted by the sparse DS-CDMA to perform multiuser detection. Thus the negative effect of channel noisy and interference can be eliminated. Computer simulation has been done. The theory analysis and simulation results show that the sparse DS-CDMA can achieve excellent performance even under serious overloading conditions.