Ergodic Capacity of Hard-Switching in Hybrid FSO/IRS-Assisted RF Transmission

This paper presents an ergodic capacity analysis of a hybrid free-space optical (FSO)/Radio-Frequency (RF) communication system with hard-switching scheme. The RF transmission is assisted by an intelligent reflecting surface (IRS). The larger bandwidth FSO link is considered as the primary communication link and the RF link having lower bandwidth is considered as the secondary communication link. When the signal-to-noise ratio (SNR) of the FSO link drops below an acceptable level, the communication link switches from the primary FSO link to the secondary RF link, and the RF transmission is assisted by an IRS. The ergodic capacity of the mixed IRS-aided RF/FSO system is derived and validated via Monte Carlo simulations. The influence of IRS element count on ergodic capacity has been elucidated, particularly at the lower SNR of the FSO link for both moderate and strong turbulences. The variation of ergodic capacity with source-destination link distance is also presented.