This paper focuses on multi-user downlink signal transmission in a wireless system aided by multiple reconfigurable intelligent surfaces (RISs). In such a multi-RIS, multi-user, multi-antenna scenario, determining a set of RIS phase shifts to maximize the sum throughput becomes intractable. Hence, we propose a novel scheme that can substantially simplify the optimization of passive beamforming. By opportunistically selecting a user with the best channel condition as the only active transmitter in the system, it degrades to single-user passive beamforming, where two methods, i.e., joint optimization based on the semidefinite relaxation approach and alternating optimization, are applicable. The superiority of the proposed scheme is demonstrated through Monte-Carlo simulations.

翻译：本文聚焦于多智能反射面（RIS）辅助无线系统中的多用户下行信号传输。在此类多RIS、多用户、多天线的场景下，确定一组RIS相移以实现总吞吐量最大化变得难以处理。为此，我们提出一种新颖方案，能够大幅简化无源波束成形的优化过程。通过机会性地选择信道条件最佳的用户作为系统中唯一的活跃发射机，该方案退化为单用户无源波束成形问题，此时可应用两种方法：基于半定松弛方法的联合优化以及交替优化。蒙特卡洛仿真验证了所提方案的优越性。