DS-CDMA developed on spread spectrum is a multiple access technology,but it is difficult for such a system to attain a satisfactory performance under overloading conditions.A sparse DS-CDMA system is presented.It is possible to represent the relationship between the chips and the 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,a belief propagation algorithm,which is suitable to the case of low density graph,was adopted by the sparse DS-CDMA to perform multiuser detection.Thus the negative effect of channel noisy and interference can be eliminated.Computer simulation was done.The theory analysis and simulation results showed that the sparse DS-CDMA can achieve excellent performance even under serious overloading conditions.%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，最大限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。
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