免调度NOMA系统中扩频码优化设计

Optimized design of spread spectrum codebooks in the grant-free NOMA system

在免调度非正交多址接入(Non-Orthogonal Multiple Access, NOMA)系统中,降低不同用户扩频码本之间的相关性对于提升系统性能至关重要。针对维度为特定值的码本,基于Zadoff-Chu矩阵结合差集序列构造了扩频码本,该码本最大互相关值μ达到Welch界;针对维度取值灵活的码本,文中提出了双重迭代最小化μ值码本优化方法,该方法结合优化门限的并行取值通过双重迭代不断降低码本各列之间的相关性。仿真结果表明,与使用其他现有扩频码本相比,使用文中算法优化的扩频码本能够提高基于多测量矢量压缩感知模型的NOMA系统的信道估计和多用户检测性能。

In the grant-free non-orthogonal multiple access(NOMA) system, reducing the correlation between spread spectrum codebooks of different users is crucial to the overall performance. For the codebooks with fixed dimensions, a spread spectrum codebook based on the Zadoff-Chu matrix is constructed by using difference set sequences, and the mutual coherence of the codebooks μ reaches the Welch bound. For the codebooks with flexible dimensions, a double iterative algorithm of minimizing the value of μ is proposed. The method incorporates the parallel setting of the values of the optimal threshold and continuously reduces the coherence between the columns of the target codebook by double iteration. Simulation results show that, compared with other existing spread spectrum codebooks, the spread spectrum codebooks optimized by the proposed algorithm can improve the channel estimation and multi-user detection performance of the NOMA system based on the multiple measurement vector-compressive sensing model.