Max-min fair RIS-aided rate-splitting multiple access for multigroup multicast communications

Rate-splitting multiple access (RSMA) can cope with a wide range of propagation conditions in multigroup multicast communications through rate splitting optimization. To breakthrough the group-rate limited bottleneck, reconfigurable intelligent surface (RIS) technique can be introduced to assist wireless communications through enhancing the channel quality. In RIS-aided RSMA multigroup multicasting, how to provide fair and high-quality multiuser service under power and spectrum constraints is essential. In this paper, we propose a max-min fair RIS-aided rate-splitting multiple access (MMF-RIS-RSMA) scheme for multigroup multicast communications, where the rate fairness is obtained by maximizing the minimum group-rate. In doing so, we jointly optimize the beamformers, the rate splitting vector at the transmitter, as well as the phase shifts at RIS. To solve it, we divide the original optimization problem into two subproblems and alternately optimize the variables. The beamforming and rate splitting optimization subproblem is solved by using the successive convex approximation technique. The phase shift optimization subproblem is solved through the penalty function method to achieve a rank-one locally optimal solution. Simulations demonstrate that the proposed MMF-RIS-RSMA scheme can obtain significant performance gain in terms of the minimum group-rate.