This study investigates the application of simultaneous transmission and reflection (STAR) enabled by reconfigurable intelligent surface (RIS) in the context of both non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA) communication systems. As an advanced technology, STAR-RIS holds significant potential to enhance the performance of NOMA networks. The primary focus of this research is to assess how STAR-RIS influences key aspects of NOMA, specifically the secrecy coverage region (SCR) and secrecy outage probability (SOP). Through a comprehensive analysis of mathematical and simulation results, valuable insights into the synergy between STAR-RIS and NOMA are derived, illuminating advancements in secure and efficient communication systems. Furthermore, by examining the impact of STAR-RIS on OMA and comparing its performance with NOMA, the study demonstrates that the integration of STAR-RIS improves NOMA’s performance, showcasing favorable outcomes compared to OM

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