RIS-Assisted Hybrid OMA-NOMA Systems with Imperfect Phase Compensation

For next-generation wireless communication systems, reconfigurable intelligent surfaces (RIS) and non-orthogonal multiple access (NOMA) are key technology enhancements. However, RIS experiences hardware impairments leading to imperfect phase compensation. In NOMA, user pairing and power allocation are critical for enhancing spectral efficiency. In this paper, we investigate the performance of RIS-assisted NOMA systems with imperfect phase compensation at the RIS. We derive bounds on the power allocation factor to ensure that the achievable data rate for each user surpasses that of a orthogonal multiple access (OMA) system. Based on these bounds, we propose various power allocation algorithms. Furthermore, we introduce a user pairing algorithm designed for hybrid OMANOMA systems, which defaults to OMA to reduce complexity if the achievable sum rate (ASR) gain falls below a specified threshold. Extensive simulations demonstrate that our algorithm outperforms state-of-the-art algorithms.