Simultaneously Transmitting and Reflecting Reconfigurable Intelligent Surface Assisted NOMA Networks

TL;DR

This paper analyzes the performance of STAR-RIS assisted NOMA networks over Rician channels, deriving outage and rate expressions, and demonstrating their superiority over OMA and cooperative systems through simulations.

Contribution

It introduces new analytical expressions for outage probability and ergodic rate in STAR-RIS-NOMA networks considering imperfect SIC, and evaluates their performance enhancements.

Findings

STAR-RIS-NOMA outperforms STAR-RIS-OMA and cooperative systems in outage probability.

Increasing reflecting elements and Rician factor improves network performance.

Ergodic rates of STAR-RIS-NOMA are higher than STAR-RIS-OMA.

Abstract

Simultaneously transmitting/refracting and reflecting reconfigurable intelligent surface (STAR-RIS) has been introduced to achieve full coverage area. This paper investigate the performance of STAR-RIS assisted non-orthogonal multiple access (NOMA) networks over Rician fading channels, where the incidence signals sent by base station are reflected and transmitted to the nearby user and distant user, respectively. To evaluate the performance of STAR-RIS-NOMA networks, we derive new approximate expressions of outage probability and ergodic rate for a pair of users, in which the imperfect successive interference cancellation (ipSIC) and perfect SIC (pSIC) schemes are taken into consideration. Based on the asymptotic expressions, the diversity orders of the nearby user with ipSIC/pSIC and distant user are achieved carefully. The high signal-to-noise ratio slopes of ergodic rates for nearby user with pSIC and distant user are equal to $one$ and $zero$, respectively. In addition, the system throughput of STAR-RIS-NOMA is discussed in delay-limited and delay-tolerant modes. Simulation results are provided to verify the accuracy of the theoretical analyses and demonstrate that: 1) The outage probability of STAR-RIS-NOMA outperforms that of STAR-RIS assisted orthogonal multiple access (OMA) and conventional cooperative communication systems; 2) With the increasing of reflecting elements $K$ and Rician factor $\kappa $, the STAR-RIS-NOMA networks are capable of attaining the enhanced performance; and 3) The ergodic rates of STAR-RIS-NOMA are superior to that of STAR-RIS-OMA.