This paper investigates the performance of vehicleto-vehicle (V2V) communications assisted by a reconfigurable intelligent surface (RIS) and a simultaneous transmitting and reflecting intelligent omni-surface (STAR-IOS) under nonorthogonal multiple access (NOMA) and orthogonal multiple access (OMA) schemes. In particular, we consider that the RIS is close to the transmitter vehicle while the STAR-IOS is near the receiver vehicles. In addition, we assume that the STAR-IOS exploits the energy-splitting (ES) protocol for communication and the fading channels between the RIS and STAR-IOS follow composite Fisher-Snedecor F distribution. Under such assumptions, we first use the central limit theorem (CLT) to derive the PDF and the CDF of equivalent channels at receiver vehicles, and then, we derive the closed-form expression of outage probability (OP) under NOMA/OMA scenarios. Additionally, by exploiting Jensen's inequality, we propose an upper bound of the ergodic capacity (EC), and then, we derive an analytical expression of the energy efficiency (EE) for both NOMA and OMA cases. Further, our analytical results, which are double-checked with the Monte-Carlo simulation, reveal that applying RIS/STAR-RIS in V2V communications can significantly improve the performance of intelligent transportation systems (ITS). Besides, the results indicate that considering the NOMA scheme provides better performance in terms of the OP, EC, and EE as compared with the OMA case for the considered V2V communication.

翻译：本文研究了在非正交多址接入（NOMA）和正交多址接入（OMA）方案下，由可重构智能表面（RIS）和同步传输反射智能全向表面（STAR-IOS）辅助的车对车（V2V）通信性能。特别地，我们考虑了RIS靠近发射车辆而STAR-IOS靠近接收车辆的场景。此外，我们假设STAR-IOS采用能量分裂（ES）协议进行通信，且RIS与STAR-IOS之间的衰落信道服从复合Fisher-Snedecor F分布。基于这些假设，我们首先利用中心极限定理（CLT）推导了接收车辆处等效信道的概率密度函数（PDF）和累积分布函数（CDF），随后推导了NOMA/OMA场景下中断概率（OP）的闭式表达式。进一步地，通过利用Jensen不等式，我们提出了遍历容量（EC）的上界，并推导了NOMA和OMA情况下能量效率（EE）的解析表达式。此外，经蒙特卡洛仿真双重验证的分析结果表明，在V2V通信中应用RIS/STAR-RIS可以显著提升智能交通系统（ITS）的性能。同时，结果表明，在所考虑的V2V通信中，相较于OMA方案，采用NOMA方案在中断概率、遍历容量和能量效率方面均能提供更优的性能。