Resource Management in RIS-Assisted Rate Splitting Multiple Access for Next Generation (xG) Wireless Communications: Models, State-of-the-Art, and Future Directions

Next Generation (xG) wireless networks require more stringent performance levels. New technologies such as Reconfigurable Intelligent Surfaces (RISs) and Rate Splitting Multiple Access (RSMA) are candidates for meeting some of the performance requirements, including higher user rates at reduced costs. RSMA provides a new way of mixing the messages of multiple users, and the RIS provides a controllable wireless environment. This paper provides a comprehensive survey on the various aspects of the synergy between RISs and RSMA for xG wireless communications systems. In particular, the paper studies more than 60 articles considering over 20 different system models where the RIS-aided RSMA system shows performance advantage (in terms of sum-rate or outage probability) over traditional RSMA models. These models include reflective RIS, Simultaneously Transmitting and Reflecting (STAR)-RIS, as well as transmissive surfaces. The state-of-the-art resource management methods for RIS-assisted RSMA communications employ traditional optimization techniques and/or machine learning techniques. We outline major research challenges and multiple future research directions.