码分多址(CDMA)技术是第三代移动通信系统的核心技术之一。由于多址干扰的存在 不仅使系统性能受到严重影响，而且限制了系统容量提高。多用户检测是一种从接 收端设计入手的干扰抑制方法，不但可以抗多址干扰，还可以抗远近效应和多径干 扰，因此成为CDMA系统的关键技术之一。 本文分别对多用户检测技术和Turbo编译码技术进行理论研究和仿真分析。在此基础 上重点研究基于Turbo译码思想的多用户检测理论和实现方法。针对Turbo多用户检 测技术中多次内外迭代所造成的系统延时问题，借鉴已有的简化算法，提出一种将 滑动窗技术和改进的Log-MAP算法（门限法）相结合的算法，称为滑动窗-门限-Log -MAP算法。该算法在Turbo译码时，将数据分成二块分别按照门限法简化Log-MAP算 法中涉及到的指数运算。同时，考虑到一个门限值带来的计算误差，提出在滑动窗- 门限-Log-MAP译码算法中，通过对相关函数 的取值设置两个门限，即函数取值区间 划分成三段，以进一步减小误差。 仿真结果表明，一个门限值的滑动窗-门限-Log-MAP译码算法性能虽然不及标准Log -MAP算法，但系统延时约为后者的1/2。两个门限值的滑动窗-门限-Log-MAP译码算 法的性能优于只有一个门限值的滑动窗-门限-Log-MAP译码算法，接近于标准Log- MAP译码算法。

CDMA has become one of the key techniques of 3G mobile communication system. However, multiple access interference (MAI) affects not only the system performance, but also the increasing of its capacity. Multi-user detection (MUD) is the way to cancel MAI from receiver. It is also good for eliminating near-far effect and multipath interference. In this paper, some techniques of MUD and Turbo code/decode are studied, and some simulations were done. Turbo MUD theories and some methods based on the idea of Turbo decoding were emphasized. To solve the problem of system delay which caused by the iterative in turbo MUD, a new algorithm named SW-Threshold-Log-MAP, combining the sliding window method with Threshold-Log-MAP, was proposed. Follow the rule of this algorithm, the received signal sequences was divided into two blocks for reducing the system delay, the threshold was set for simplifying the complexity of exponent operation in decoding. At the same time, considering that one threshold may produce more errors, another SW-Threshold-Log-MAP with two thresholds was presented. In this algorithm, the value domain of correlation function was divided into three regions. Simulation results show that the bit error rate of SW-Threshold-Log-MAP with one threshold is higher than standard Log-MAP algorithm, but the system delay is reduced to half of the standard Log-MAP algorithm. The performance of SW-Threshold-Log-MAP with two thresholds is better than the one with one threshold, and its performance is more approached to standard Log-MAP algorithm.