Joint active and passive beamforming optimization for multigroup multicast system aided by intelligent reflecting surface

Abstract An intelligent‐reflecting‐surface aided multigroup multicast communication system is investigated in this paper. We develop energy‐efficient designs for both the precoding matrix at the base station and passive reflecting beamforming at intelligent‐reflecting‐surface, subject to the minimum signal‐to‐interference‐plus‐noise ratio constraint of each user and the unit‐modulus constraint imposed by passive intelligent‐reflecting‐surface. This leads to a complex non‐convex problem for which to tackle we propose two novel algorithms based on alternating optimization techniques. Specifically, one algorithm employs semi‐definite relaxation to obtain the suboptimal reflection coefficient vector and suboptimal precoding vector for each group. In order to reduce the computational complexity, the second algorithm transforms this non‐convex problem into two second‐order cone programming problems. Numerical results show that intelligent‐reflecting‐surface can significantly reduce the power consumption of the base station.