Enhancing RIS-Aided Two-Way Full-Duplex Communication With Nonorthogonal Multiple Access

This article proposes a reconfigurable intelligent surface (RIS)-aided two-way full-duplex communication with nonorthogonal multiple access transmission schemes to improve spectrum utilization. Besides, the joint impact of error phase-shift quantization, imperfect successive interference cancellation (SIC), and residual loop interference on the system performance have also been investigated. Under Nakagami-
${m}$
fading channels, approximate closed-form expressions for the outage performance and the ergodic rate are derived. Through asymptotic analyses, some insights are achieved, including the diversity order, the coding gain, and the ergodic slope. Moreover, three adaptive power allocation (PA) optimization problems are formulated aiming to: 1) minimize outage probability; 2) achieve max–min rate fairness; and 3) maximize the user’s sum rate subject to the Quality-of-Service constraint. Simulation results not only validate the theoretical analyses and the optimal/suboptimal solutions but also reveal three following observations. First, the considered system outperforms the orthogonal multiple access baseline. Second, increasing the number of control bits for the error phase-shift quantization and/or the number of RIS’s elements can significantly reduce the impact of imperfect SICs. Third, employing one of three adaptive PA solutions improves the system’s performance significantly.