Sum Rate Maximization With Discrete Phase Shift for Reconfigurable Intelligent Surface Aided Broadcast Channel

This work considers two-user broadcast channel aided by reconfigurable intelligent surface (RIS) with discrete phase shift. The sum rate is maximized where the precoding vectors and the RIS matrix are jointly optimized. The nonconvex problem is approximated through maximum ratio transmission, optimal power allocation and Courant penalty techniques. Two algorithms are proposed for the approximated combinatorial problem based on the alternating direction method of multipliers and the proximal gradient ideas, respectively. Simulations show that the proposed algorithms achieve higher sum rate with much lower computational cost than the state of the art models.