Max-Min Fair Beamforing Design for a RIS-Assisted System with SWIPT

This paper investigates a multiuser reconfigurable intelligent surface (RIS)-assisted simultaneous wireless information and power transfer (SWIPT) system, in which a RIS assists in establishing favorable wireless communication environment. Particularly, we study the max-min signal-to-interference-plus-noise ratio (SINR) problem of the system by joint optimizing the base station (BS) active beamforming vectors, the RIS passive beamforming vector, and the power splitting (PS) ratios while guaranteeing the BS maximum transmit power budget and the minimum harvested energy threshold. The considered max-min SINR problem is highly non-convex, which is arduous to directly solve. Hence, we present an efficient alternating optimization (AO) algorithm to decompose the max-min SINR problem into three tractable subproblems, which are solved in an alternating manner. Particularly, we apply semi-definite relaxation (SDR) technique and the bisection method to tackle the beamforming optimization subproblems, and then derive a closed-form solution to solve the PS ratios optimization subproblem. Numerical simulations verify the superiority of our proposed AO algorithm and demonstrate that deploying RIS can achieve significantly increased min-SINR value.