Energy Efficient Rate Splitting Multiple Access with Active Reconfigurable Intelligent Surface

Rate Splitting Multiple Access (RSMA) has been considered as a innovative multiple access technique capable of efficiently managing inter-user interference and enhancing the robustness of wireless communication systems. However, the performance of RSMA remains constrained by the weakest user channel gain, which can significantly limit achievable data rates. Reconfigurable intelligent surface (RIS), as a promising technology for enhancing wireless transmission performance by precisely creating favorable propagation environment, has been considered as a beneficial integration into RSMA-aided wireless systems. The RIS assisted RSMA system has attracted substantial research interest, though most existing studies focus on passive RIS and RSMA, ignoring the severe power attenuation from the multiplicative effects of RIS incidence and reflection path loss. In this paper, we investigate an active RIS-assisted RSMA downlink system and formulate an energy efficiency maximization problem that jointly optimizes the base station beamforming matrix, rate allocation vector, and RIS reflection coefficients matrix. Simulation results demonstrate that the proposed active RIS-aided RSMA scheme achieves improved energy efficiency (EE) than active RIS-aided SDMA and passive RIS-aided RSMA scheme.