# Mixed RF/FSO Relaying Systems with Hardware Impairments

## TL;DR

This paper analyzes a dual-hop RF/FSO relaying system with hardware impairments, proposing a partial relay selection protocol and deriving closed-form expressions for key performance metrics.

## Contribution

It introduces a novel impairment model and a unified FSO channel model, providing new analytical expressions for system performance under realistic conditions.

## Key findings

- Outage probability and bit error rate are derived in closed-form.
- Hardware impairments significantly affect system performance.
- The proposed models are validated through Monte Carlo simulations.

## Abstract

In this work, we provide a detailed analysis of a dual-hop fixed gain (FG) amplify-and-forward relaying system, consisting of a hybrid radio frequency (RF) and free-space optical (FSO) channels. We introduce an impairment model which is the soft envelope limiter (SEL). Additionally, we propose the partial relay selection (PRS) protocol with outdated channel state information (CSI) based on the knowledge of the RF channels in order to select one relay for the communication. Moreover, the RF channels of the first hop experience Rayleigh fading while we propose a unified fading model for the FSO channels, called the unified Gamma Gamma (GG), taking into account the atmospheric turbulence, the path loss and the misalignment between the transmitter and the receiver aperture also called the pointing error. Novel closed-forms of the outage probability (OP), the bit error probability (BEP) and the average ergodic capacity (EC) are derived in terms of Meijer-G and Fox-H functions. Capitalizing on these metrics, we also derive the asymptotical high signal-to-noise ratio (SNR) in order to get engineering insights into the impacts of the hardware impairments and the system parameters as well. Finally, using Monte Carlo simulations, we validate numerically the derived mathematical formulations.