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首页> 外文期刊>IEEE Transactions on Vehicular Technology >A Low-Complexity SISO Multiuser Detector for Iterative Decoding of Asynchronous CDMA Systems With Convolutional Codes
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A Low-Complexity SISO Multiuser Detector for Iterative Decoding of Asynchronous CDMA Systems With Convolutional Codes

机译：具有卷积码的异步CDMA系统迭代解码的低复杂度SISO多用户检测器

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摘要

The optimal decoding scheme for asynchronous code-division multiple-access (CDMA) systems that employ convolu-tional codes results in a prohibitive computational complexity. To reduce the computational complexity, an iterative receiver structure was proposed for decoding multiuser data in a convolutional coded CDMA system. At each iteration, extrinsic information is exchanged between a soft-input soft-output (SISO) multiuser detector and a bank of single-user SISO channel decoders. A direct implementation of the optimal SISO multiuser detector, however, has exponential computational complexity in terms of the number of users which is still prohibitive for channels with a medium to large number of users. This paper presents a low-complexity SISO multiuser detector using the decision-feedback scheme, of which tentative hard decisions are made and fed back to the SISO multiuser from the previous decoding output. In the proposed scheme, the log-likelihood ratios (LLR) as well as the tentative hard decisions of code bits are fed back from the SISO decoders. The hard decisions are used to constrain the trellis of the SISO multiuser detector and the LLRs are used to provide a priori information on the code bits. The detector provides good performance/complexity tradeoffs. The computational complexity of the detector can be set to be as low as linear in the number of users. Simulations show that the performance of the low-complexity SISO multiuser detector approaches that of the single-user system for moderate to high signal-to-noise ratios even for a large number of users.
机译：使用卷积码的异步码分多址（CDMA）系统的最佳解码方案导致计算复杂性过高。为了降低计算复杂度，提出了一种迭代接收器结构，用于在卷积编码CDMA系统中解码多用户数据。在每次迭代中，外部信息在软输入软输出（SISO）多用户检测器和一组单用户SISO通道解码器之间交换。然而，就用户数量而言，最佳SISO多用户检测器的直接实现具有指数计算复杂性，这对于中到大量用户的信道仍然是禁止的。本文提出了一种使用决策反馈方案的低复杂度SISO多用户检测器，该算法将做出初步的硬性决策，并从先前的解码输出反馈给SISO多用户。在提出的方案中，从SISO解码器反馈对数似然比（LLR）以及代码位的暂定硬决策。硬性决定用于约束SISO多用户检测器的网格，而LLR用于提供有关代码位的先验信息。该检测器提供了良好的性能/复杂度折衷。可以将检测器的计算复杂度设置为与用户数量一样低。仿真表明，即使对于大量用户，对于中等到高的信噪比，低复杂度SISO多用户检测器的性能也接近单用户系统。

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