Energy-Efficient Optimization Algorithm Based on Reconfigurable Intelligent Surface and Rate Splitting Multiple Access for 6G Multicell Communication System

Reconfigurable intelligent surface (RIS) is a technology that can intelligently control the signal transmission link to enhance the signal transmission quality. Rate splitting multiple access (RSMA) technology can effectively restrain the same channel interference between users and achieve better system performance by flexibly controlling the rate allocation strategy and beamforming strategy. In this article, we combine RSMA with RIS and propose an energy efficiency optimization algorithm for 6G multicell communication system. We first formulate an optimization problem which is to maximize energy efficiency of the system by jointly optimizing beamforming vectors of base stations (BSs), phase shifts matrix of RISs, and rate allocation matrix of users. Then, in order to solve this nonconvex optimization problem, we decouple the original problem into two subproblems: 1) beamforming optimization and 2) phase shifts optimization. For the former, we use the successive convex approximation (SCA) method to get the solution, and for the latter, we adopt semidefinite relaxation and exterior point methods to solve. In addition, we analyze the complexity of the proposed algorithm. Simulation result shows that compared with space division multiple access (SDMA) and nonorthogonal multiple access (NOMA), the proposed mechanism in this article can significantly improve system energy efficiency.