Distributed RIS-assisted mmWave multi-user MIMO beamspace system

We are considering a novel distributed reconfigurable intelligent surfaces assisted (RIS-assisted) millimeter -wave (mmWave) multi-user multi-input multi-output (MIMO) beamspace system. Beamspace systems offer a low-scattering communication to users through beams. To enrich the propagation environment, multiple reconfigurable intelligent surfaces are installed on top of the surrounding buildings to provide an additional communication link, between the base station and users, by introducing phase shifts in the incoming signal arriving at it. Such systems allow the selection of two distinct beams for each user. The first beam is directly steered towards the user and the second beam is steered to the user via RIS. The selection of desirable beams is required to reduce the number of radio frequency (RF) chains at the transmitter. In this paper, we propose a beam selection algorithm that can assign two distinct and unshared beams to each user after optimally adjusting the phases of each RIS. Additionally, we propose a max-min fairness power allocation scheme to obtain a minimum achievable rate for each user. Simulation results compare the sum-rate performance with the existing beam selection algorithms.