Ergodic Performance Analysis of Reconfigurable Intelligent Surface Enabled Bidirectional NOMA

This paper proposes and investigates a reconfigurable intelligent surface (RIS) enabled bidirectional non-orthogonal multiple access (NOMA) network termed as NOMA-RIS. Here, RIS allows multiple NOMA users in one group to communicate with or share information with multiple NOMA users in another group. Specifically, the two NOMA user groups send the data intended for exchange to the RIS. RIS reflects the NOMA signals allowing bidirectional communication between two NOMA user groups. In particular, under the Rician fading environment, we pay close attention to how well RIS-enabled bidirectional NOMA networks operate. Analytical expressions for tight upper bounds for the ergodic capacity are mathematically derived and verified with the simulation results. Comprehensive performance comparisons are presented, showing that our proposed bidirectional NOMA-RIS system can achieve enhanced capacity gains than RIS-enabled traditional orthogonal multiple access schemes. These comparisons also offer practical insights into the impact of various system parameters on the overall network performance.