In this paper, we analyze the performance of a reconfigurable intelligent surface (RIS)-assisted multi-hop transmission by employing multiple RIS units to enable favorable communication for a mixed free-space optical (FSO) and radio-frequency (RF) system. We consider a single-element RIS since it is hard to realize phase compensation for multiple-element RIS in the multi-hop scenario. We develop statistical results for the product of the signal-to-noise ratio (SNR) of the cascaded multiple RIS-equipped wireless communication. We use decode-and-forward (DF) and fixed-gain (FG) relaying protocols to mix multi-RIS transmissions over RF and FSO technologies and derive probability density and distribution functions for both the relaying schemes by considering independent and nonidentical double generalized gamma (dGG) distribution models for RF transmissions with line-of-sight (LOS) and inverse-Gamma shadowing effect and atmospheric turbulence for FSO system combined with pointing errors. We analyze the outage probability, and average bit-error rate (BER) performance of the considered system. We also present an asymptotic analysis of the outage probability using gamma functions to provide insight into the considered system in the high SNR regime. We use computer simulations to validate the derived analytical expressions and demonstrate the performance for different system parameters on the RIS-assisted multi-hop transmissions for a vehicular communication system.

翻译：本文分析了可重构智能表面（RIS）辅助的多跳传输性能，通过部署多个RIS单元为混合自由空间光（FSO）与射频（RF）系统实现有利通信。由于在多跳场景中难以实现多元素RIS的相位补偿，我们采用单元素RIS。我们推导了级联多RIS无线通信信噪比乘积的统计结果。采用解码转发（DF）和固定增益（FG）中继协议实现RF与FSO技术上的多RIS传输混合，并考虑RF传输中具有视距（LOS）和逆伽马阴影效应的独立非恒等双广义伽马（dGG）分布模型，以及FSO系统中结合指向误差的大气湍流效应，推导了两种中继方案的概率密度函数与分布函数。分析了所考虑系统的中断概率和平均误码率（BER）性能。同时利用伽马函数对中断概率进行渐近分析，以揭示高信噪比下系统的性能特性。通过计算机仿真验证了理论表达式的准确性，并展示了不同系统参数下RIS辅助多跳传输在车载通信系统中的性能表现。