Mixed FSO/IRS-Aided NOMA Network with Heterogeneous Channels

This study analyzes the performance of a two-hop communication system that integrates free-space optical (FSO) transmission with intelligent reflecting surface (IRS)-aided radio frequency (RF) transmission. This analysis focuses on the transmission within a non-orthogonal multiple access (NOMA) system over heterogeneous channels: the source-to-relay FSO channel follows a Fisher-Snedecor <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$F$</tex> distribution, the relay-to-users RF channels are modeled as Rayleigh distributions, the relay-to-IRS and IRS-to-users RF channels are characterized by Rician distributions. A closed-form expression for the outage probability has been derived and approximated as a Gamma distribution using the moment-generating function under imperfect successive interference cancellation. Notably, the outage probability expressions and their approximation closely align with our simulation results, thus validating the accuracy of our findings. Additionally, an asymptotic expression for the outage probability has been derived, particularly in the FSO transmit SNR regime, and the corresponding diversity order is evaluated. The impact of various system parameters, such as turbulence, on the rate of decay of the outage probability is explained through the diversity order.