准大稀疏序列CDMA：线性复LAS检测器的单用户约束方法
Quasi-Large Sparse-Sequence CDMA: Approach to Single-User Bound by Linearly-Complex LAS Detectors
摘要：
我们提出了一种准大随机序列（QLRS）CDMA，其中K个用户通过一个频谱扩展因子为N的公共信道接入一个点。每个比特由时间扩展因子B扩展，并在时间和频率上扩展的BN码片随机序列上跳跃。每个用户复用并发送B个扩展比特，并且总信道负载为α = K/N比特/s/Hz。线性复数LAS检测器检测传输的比特。当B趋于无穷大时，如果α < 1/2 - 1/（4ln ~ 2），则每个发送比特在高SNR状态下达到BER的单比特界，就好像没有干扰比特一样。在仿真中，当比特数BK >= 500时，每个比特可以接近高达1比特/秒/赫兹的α的单比特界限。在本文中，我们进一步提出了准大稀疏序列（QLSS）CDMA，它是将QLRS-CDMA中的稠密序列替换为稀疏序列。仿真结果表明，当非零码片数仅为16时，误码率已经接近于QLRS-CDMA，而由于序列稀疏性，复杂度显著降低。
英文摘要：
We have proposed a quasi-large random-sequence (QLRS) CDMA where K users access a point through a common channel with spectral spreading factor N. Each bit is extended by a temporal spreading factor B and hopped on a BN-chip random sequence that is spread in time and frequency. Each user multiplexes and transmits B extended bits and the total channel load is alpha = K/N bits/s/Hz. The linearly-complex LAS detectors detect the transmitted bits. We have obtained that as B tends to infinity, if alpha < 1/2 - 1/(4ln2), each transmitted bit achieves the single-bit bound in BER in high SNR regime as if there was no interference bit. In simulation, when bit number BK >= 500, each bit can approach the single-bit bound for alpha as high as 1 bit/s/Hz. In this paper, we further propose the quasi-large sparse-sequence (QLSS) CDMA by replacing the dense sequence in QLRS-CDMA with sparse sequence. Simulation results show that when the nonzero chips are as few as 16, the BER is already near that of QLRS-CDMA while the complexity is significantly reduced due to sequence sparsity.
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