Multiuser beamforming is considered for partially-connected millimeter wave massive MIMO systems. Based on perfect channel state information (CSI), a low-complexity hybrid beamforming scheme that decouples the analog beamformer and the digital beamformer is proposed to maximize the sum-rate. The analog beamformer design is modeled as a phase alignment problem to harvest the array gain. Given the analog beamformer, the digital beamformer is designed by solving a weighted minimum mean squared error problem. Then based on imperfect CSI, an analog-only beamformer design scheme is proposed, where the design problem aims at maximizing the desired signal power on the current user and minimizing the power on the other users to mitigate the multiuser interference. The original problem is then transformed into a series of independent beam nulling subproblems, where an efficient iterative algorithm using the majorization-minimization framework is proposed to solve the subproblems. Simulation results show that, under perfect CSI, the proposed scheme achieves almost the same sum-rate performance as the existing schemes but with lower computational complexity; and under imperfect CSI, the proposed analog-only beamforming design scheme can effectively mitigate the multiuser interference.

翻译：针对部分连接的毫米波大规模MIMO系统，研究了多用户波束赋形问题。基于完美信道状态信息（CSI），提出了一种低复杂度的混合波束赋形方案，该方案通过解耦模拟波束赋形器和数字波束赋形器以最大化总速率。模拟波束赋形器设计被建模为相位对齐问题以获取阵列增益。在给定模拟波束赋形器的情况下，通过求解加权最小均方误差问题设计数字波束赋形器。进而，基于非完美CSI提出了一种纯模拟波束赋形设计方案，该设计问题旨在最大化当前用户期望信号功率并最小化其他用户功率以抑制多用户干扰。将原问题转化为一系列独立的波束零陷子问题，并基于优化最小化框架提出了一种高效迭代算法求解这些子问题。仿真结果表明：在完美CSI条件下，所提方案能以更低计算复杂度实现与现有方案几乎相同的总速率性能；在非完美CSI条件下，所提纯模拟波束赋形设计方案能有效抑制多用户干扰。