Adaptive-Combining-Based RIS-Aided Hybrid FSO/RF System: A Performance Analysis

Free space optics (FSO) communication is seen as a cost-effective way to provide higher bandwidth, higher data rates, better link security, and higher immunity to interference compared to radio frequency (RF) communication over short link distances. Despite these advantages, FSO link is severely affected by pointing errors, atmospheric turbulence, and signal loss due to the obstructions caused by buildings, trees, mountains, etc. In this paper, we propose a hybrid FSO/RF communication system model consisting of a FSO subsystem backed by a reliable RF subsystem considering adaptive-combining-based switching scheme. In addition, both the FSO and RF subsystems are assisted by reconfigurable intelligent surfaces (RIS). The main goal is to improve the system reliability compared to the existing FSO and hybrid FSO/RF systems with RIS. Specifically, we carry out the performance analysis of the adaptive-combining-based RIS-aided hybrid FSO/RF system by deriving the closed-form expressions for outage probability and average symbol error rate (SER) assuming heterodyne detection technique. The numerical results, accompanied by in-depth discussions, reveal that the proposed system outperforms both the existing RIS-aided FSO and the RIS-aided hybrid FSO/RF systems employing a hard-switching scheme.