Outage Performance Analysis of HARQ Assisted STAR-RIS-NOMA/RSMA for V2V Communications

Abstract

As a key enabling technology for sixth-generation (6G) wireless communication systems, the simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) can dynamically reconfigure its electromagnetic elements to effectively extend wireless network coverage. The deployment of STAR-RIS in vehicle-to-vehicle (V2V) communications effectively mitigates vehicle non-line-of-sight transmission issues and improves the reliability of vehicular communication. This paper investigates two typical multiple access schemes, namely non-orthogonal multiple access (NOMA) and rate splitting multiple access (RSMA). Considering both perfect and imperfect successive interference cancellation (SIC) conditions, we adopt hybrid automatic repeat request (HARQ) technology to further enhance communication reliability. We analyze the outage performance of receiving vehicles in HARQ-aided STAR-RIS-NOMA/RSMA systems and derive the closed-form expressions for outage probability. Numerical simulations validate the correctness of the theoretical derivations and reveal the following results. First, for both multiple access schemes, RSMA delivers better system performance than NOMA, and the systems under perfect SIC outperform those under imperfect SIC. Second, the introduction of HARQ can significantly boost the performance of STAR-RIS-NOMA/RSMA V2V communication systems.