Performance Analysis of RIS-Aided NOMA-Based CDRT Systems With Multiple Decode-and- Forward Relays Over Nakagami-m Fading Channels

This paper presents a novel wireless communication framework that integrates reconfigurable intelligent surfaces (RIS) and multiple decode-and-forward relays into a coordinated direct and relay transmission (CDRT) architecture based on non-orthogonal multiple access (NOMA). The system operates over Nakagami-m fading channels and employs discrete RIS phase-shift alignment, coupled with imperfect successive interference cancellation. The proposed architecture extends conventional CDRT systems by incorporating an RIS and a distributed network of decode-and-forward relays to enhance signal transmission between a source node and two user terminals-near and far users. Accordingly, closed-form expressions of key performance metrics, involving outage probability and ergodic capacity for the long information paradigm, and average block error rate (ABLER) for the short-packet communication paradigm, are derived to evaluate the system performance. Theoretical analyses are corroborated by Monte Carlo simulations, which highlight substantial performance gains with an increased number of RIS elements, particularly in discrete phase-shift configurations. Additionally, the deployment of multiple relays proves beneficial in scenarios with phase shift uncertainties. This advanced system provides a more resilient and efficient communication paradigm, addressing improving the CDRT systems’ performance.