In this letter, we investigate the signal-to-interference-plus-noise-ratio (SINR) maximization problem in a multi-user massive multiple-input-multiple-output (massive MIMO) system enabled with multiple reconfigurable intelligent surfaces (RISs). We examine two zero-forcing (ZF) beamforming approaches for interference management namely BS-UE-ZF and BS-RIS-ZF that enforce the interference to zero at the users (UEs) and the RISs, respectively.Then, for each case, we resolve the SINR maximization problem to find the optimal phase shifts of the elements of the RISs. Also, we evaluate the asymptotic expressions for the optimal phase shifts and the maximum SINRs when the number of the base station (BS) antennas tends to infinity. We show that if the channels of the RIS elements are independent and the number of the BS antennas tends to infinity, random phase shifts achieve the maximum SINR using the BS-UE-ZF beamforming approach. The simulation results illustrate that by employing the BS-RIS-ZF beamforming approach, the asymptotic expressions of the phase shifts and maximum SINRs achieve the rate obtained by the optimal phase shifts even for a small number of the BS antennas.

翻译：本文研究了在多可重构智能表面（RIS）辅助的多用户大规模多输入多输出（massive MIMO）系统中，信干噪比（SINR）最大化问题。针对干扰管理，我们考察了两种迫零（ZF）波束成形方法，即BS-UE-ZF和BS-RIS-ZF，它们分别将用户（UE）和RIS处的干扰置零。随后，针对每种情况，我们求解SINR最大化问题以确定RIS各单元的最优相移。此外，我们评估了当基站（BS）天线数趋于无穷时，最优相移与最大SINR的渐近表达式。研究结果表明：若RIS单元信道独立且BS天线数趋于无穷，采用BS-UE-ZF波束成形方法时，随机相移即可实现最大SINR。仿真结果进一步显示，即使BS天线数较少，采用BS-RIS-ZF波束成形方法所得的相移渐近表达式与最大SINR渐近表达式依然能够达到由最优相移所获得的速率性能。