A future millimeter-wave (mmWave) massive multiple-input and multiple-output (MIMO) system may serve hundreds or thousands of users at the same time; thus, research on multiple access technology is particularly important.Moreover, due to the short-wavelength nature of a mmWave, large-scale arrays are easier to implement than microwaves, while their directivity and sparseness make the physical beamforming effect of precoding more prominent.In consideration of the mmWave angle division multiple access (ADMA) system based on precoding, this paper investigates the influence of the angle distribution on system performance, which is denoted as the angular multiplexing gain.Furthermore, inspired by the above research, we transform the ADMA user grouping problem to maximize the system sum-rate into the inter-user angular spacing equalization problem.Then, the form of the optimal solution for the approximate problem is derived, and the corresponding grouping algorithm is proposed.The simulation results demonstrate that the proposed algorithm performs better than the comparison methods.Finally, a complexity analysis also shows that the proposed algorithm has extremely low complexity.

翻译：未来毫米波（mmWave）大规模多输入多输出（MIMO）系统可能同时服务于数百甚至数千个用户；因此，多址接入技术的研究尤为重要。此外，由于毫米波的短波长特性，大规模阵列比微波更易实现，而其方向性和稀疏性使得预编码的物理波束赋形效果更加突出。考虑基于预编码的毫米波角度分多址（ADMA）系统，本文研究了角度分布对系统性能的影响，并将其定义为角复用增益。进一步地，受上述研究的启发，我们将最大化系统总速率的ADMA用户分组问题转化为用户间角度间隔均衡问题。随后，推导了近似问题最优解的形式，并提出了相应的分组算法。仿真结果表明，所提算法性能优于对比方法。最后，复杂度分析也表明所提算法具有极低的复杂度。