Deterministic Spreading Sequences for the Reverse Link of DS-CDMA With Noncoherent $M$-ary Orthogonal Modulation: Impact and Optimization
Deterministic Spreading Sequences for the Reverse Link of DS-CDMA With Noncoherent $M$-ary Orthogonal Modulation: Impact and Optimization
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DOI：
10.1109/tvt.2007.904516
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发表时间：
2008
影响因子：
6.8
通讯作者：
Q. Shi;Keith Q. T. Zhang
中科院分区：
文献类型：
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作者：
Q. Shi;Keith Q. T. Zhang
具有非相干检测的正交调制是直接序列码分多址（DS-CDMA）反向链路的一种有吸引力的方案。本文对具有随机扩频序列的DS-CDMA系统的性能进行了深入的研究。然而，对于具有确定性扩频序列的系统，尽管从减少多址干扰的角度来看它们很重要，但令人满意的工作还很少。为了填补这一空白，本文考虑了确定性扩展序列。本文首先对加性高斯白噪声（AWGN）和多径瑞利衰落信道下正交调制的DS-CDMA反向链路进行了详细的误差性能分析。然后，我们将DS-CDMA系统的扩频序列设计表述为一个非线性离散优化问题。序列优化主要分为两个步骤：(1)对单个二进制码矩阵进行排列，并在候选码矩阵上施加Kronecker积结构，生成较大的码空间；(2)采用进化算法高效地进行优化。数值算例表明，优化后的序列显著提高了系统性能，特别是在用户数量相对较少或考虑AWGN信道的情况下。此外，我们提出的方法可以在代码性能和搜索复杂性之间进行很好的权衡。
M-ary orthogonal modulation with noncoherent detection is an attractive scheme for the reverse link of direct-sequence code-division multiple access (DS-CDMA). The performance analysis of such DS-CDMA systems with random spreading sequences has been thoroughly studied. However, little satisfactory work has been done for systems with deterministic spreading sequences, regardless of their importance from the viewpoint of multiple-access interference reduction. To fill this void, we consider deterministic spreading sequences in this paper. We first present a detailed error performance analysis for the reverse link of DS-CDMA with -ary orthogonal modulation on both additive white Gaussian noise (AWGN) and multipath Rayleigh-fading channels. Then, we formulate the design of spreading sequences for the DS-CDMA system as a nonlinear discrete optimization problem. Two steps are taken to complete the task of sequence optimization: (1) A large code space is generated by permutating a single binary code matrix and imposing a Kronecker product structure on candidate code matrices, and (2) an evolutionary algorithm is applied to efficiently perform optimization. Numerical examples show that the optimized sequences considerably improve the system performance, especially when the number of users is relatively small or an AWGN channel is considered. In addition, our proposed approach can make a good tradeoff between code performance and search complexity.