Outage Probability Minimization in a Multi-User RIS-Assisted RSMA System

In this paper, the problem of outage probability min-imization in a Reconfigurable Intelligent Surface (RIS)-assisted Rate-Splitting Multiple Access (RSMA)-based multi-user network is investigated. The Access Point (AP) serves Near Users (NUs) and Cell Edge Users (CEUs) through a RIS, and the objective is to improve fairness by minimizing the maximum outage probability among all users. The problem is formulated as a min-max outage probability problem, which can be written as a nonlinear program but cannot be solved using conventional methods. Thus, we propose an iterative Sequential Quadratic Programming (SQP)-based search algorithm that can solve the problem efficiently. The simulation results show a similar performance of the proposed solution as compared to the Exhaustive Search (ES) method for both RSMA and Non-Orthogonal Multiple Access (NOMA). Moreover, the proposed solution achieves significant reduction in complexity order when compared to the ES solution while outperforming baseline methods.