SLNR-Based Precoding for Multi-User Communications Assisted with Reconfigurable Surfaces (Invited Paper)

Wireless communications via reconfigurable intelligent surfaces (RIS) are envisioned to offer unprecedented spectral efficiency gains by smartly inducing phase shifts on the impinging electromagnetic waves at the RIS to reconfigure the underlying propagation environment. This work investigates a multi-user downlink communication system in which the access point, equipped with multiple antennas, serves its associated single-antenna users equipments (UE) with the help of RIS. The proposal is a leakage-based design in which the transmit precoding, the power allocation, and the phase shifts of the RIS, are designed to maximize the minimum signal-to-Ieakage-plus-noise power ratio (SLNR) of the UEs subject to the constraint on the power budget of the access point. The merits of the SLNR-based approach are highlighted, e.g., reduced complexity, and simulation results show that the RIS-aided design can achieve massive MIMO gains with much fewer number of active antennas in the access point as compared to conventional relaying.