Performance of STAR-RIS-aided cooperative NOMA networks under Nakagami-m fading

In this work, we investigate the performance of the cooperative non-orthogonal multiple access (CNOMA) downlink wireless communication system assisted by the newly emerged technology of simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RISs) over Nakagami-m fading channels. Specifically, outage probability (OP), spectral efficiency (SE), and energy efficiency (EE) are used as the performance metrics. The near user's mathematically intractable probability density and cumulative distribution functions were approximated through the Gamma moment-matching technique. This was followed by the derivation of the users’ closed-form OP and ergodic rates expressions, where the latter was used to determine the SE and EE of the system. Further, extensive Monte-Carlo simulations confirmed the correctness of the obtained analytical findings. In addition, to inspect the usefulness of CNOMA in the proposed communication system, the comparison with its NOMA counterpart was incorporated into the numerical results. Finally, it was found that the cooperative link can further enhance the SE and EE of the STAR-RIS-based NOMA network.