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在本文中,我们将详细阐述一种基于DS-CDMA系统的Turbo码编码的迭代多用户接收机。这种接收机包括一个改进了的去相关反馈判决检测器(MDDFD)和K个单用户Turbo码解码器,其中K代表DS-CDMA系统中的用户数。MDDFD是在最大似然算法的理论基础上获得的,并且它能利用不同用户的Turbo码解码器输出的相关信息。另外,MDDFD也能把通常当作相互干扰的噪声而忽略的软信息传递给Turbo码解码器。同时,转移矩阵的计算也要做相应的修改。性能分析和计算机仿真都表明:不同用户的Turbo码解码器输出的相关软信息能提高MDDFD的多用户检测的容量。计算机仿真也反应出:本文提出的迭代多用户接收机若以比特错误概率来衡量,它的性能要优于传统的基于DDFD的多用户接收机。
In this paper, we describe in detail an iterative multi-user receiver based on the Turbo code of the DS-CDMA system. The receiver includes an improved decorrelation feedback decision detector (MDDFD) and K single-user Turbo code decoders, where K represents the number of users in the DS-CDMA system. MDDFD is obtained on the basis of the maximum likelihood algorithm, and it can make use of the information output from Turbo code decoders of different users. In addition, MDDFD can also pass soft information that is usually ignored as noise of mutual interference to the Turbo code decoder. At the same time, the calculation of transfer matrix must also be modified accordingly. Both performance analysis and computer simulation show that the soft information output by Turbo codecs from different users improves the MDDFD’s multi-user detection capabilities. Computer simulation also reflects that the iterative multiuser receiver proposed in this paper is better than the traditional multiuser receiver based on DDFD if it is measured by the bit error probability.