Average Symbol Error Probability of RIS-assisted Mixed RF-FSO Communication System for Uplink Network

This paper investigates the average symbol error probability (ASEP) of an uplink relaying system that integrates a reconfigurable intelligent surface (RIS) with a mixed RF–FSO (radio frequency–free space optical) link, utilizing robust opportunistic user scheduling at the RF source. The proposed model is particularly suited for deployment in environments where fiber optic infrastructure is impractical, such as in military operations, maritime regions, and rugged terrains. The analysis considers Nakagami-m fading for the RF link and Gamma-Gamma fading for the FSO link, incorporating heterodyne detection for the ASEP. A closed-form expression for ASEP is derived, revealing that system performance improves as atmospheric turbulence conditions shift from strong to weak. Additionally, it is observed that higher values of the pointing error parameter contribute positively to ASEP performance. The theoretical results are corroborated through Monte Carlo simulation.