Performance Analysis of RIS-Aided FSO/RF Hybrid Satellite-Terrestrial Network With Imperfect CSI

This study proposes an uplink reconfigurable intelligent surface (RIS)-aided free-space optical (FSO) and radio frequency (RF) hybrid satellite-terrestrial network (HSTN). We consider the impact of imperfect channel state information (CSI) on the RIS system under fixed-gain amplify-and-forward (AF) and decode-and-forward (DF) relay conditions. We derive closed-form expressions for various performance metrics of the end-to-end signal-to-noise ratio (SNR). We model the FSO link using the Málaga ($\mathcal {M}$) distribution with two detection schemes and use an RIS-aided Rayleigh fading model for the RF link, both of which consider the satellite-terrestrial loss. At high SNRs, we determine the relevant asymptotic expressions and validate the analytical results through Monte Carlo simulations. Additionally, we evaluate the impacts of key system parameters, such as RIS configuration parameters and imperfect CSI, on the end-to-end performance.

I. Introduction

Satellite communications (SatComs), offering wider coverage and higher transmission rates, have become increasingly integrated into the Internet of Things (IoT) domain, driving their applications across various fields [1]. These include media broadcasting and backhaul communications [2]. Geostationary earth orbit (GEO) satellites are widely utilized in satellite communication systems, which provide extensive coverage and are continuously visible from a fixed position on the earth for 24 hours, with minimal doppler shift. As a result, the ground-based receivers required are less complex [3], [4]. In recent years, SatComs have become essential for providing uninterrupted global connectivity, particularly in remote areas where terrestrial networks are either absent or impractical to deploy [5], [6]. Despite their numerous advantages, satellite systems typically face huge challenges, such as deep shadowing caused by obstacles between the transmitter and receiver. Moreover, the multipath effect caused by scattering in the vicinity of terrestrial receptors additionally induces many non-line-of-sight (non-LoS) signals. These issues create a masking effect that disrupts LoS communications [7], [8]. Consequently, the performance of the satellite-terrestrial link can be severely degraded and even interrupted. To mitigate these issues, hybrid satellite-terrestrial networks (HSTNs) have become a viable solution, delivering high throughput across broad coverage areas. By combining satellite communications with terrestrial networks, HSTNs provide critical services in broadcasting, navigation, and emergency communications in natural disasters. Despite the support from terrestrial communication infrastructure, HSTNs are more or less affected by the masking effect caused by shadowing and physical obstructions, which occasionally could still disrupt LoS communications between satellites and ground transmitters. To further mitigate this issue, terrestrial relays are utilized within HSTNs to enhance communication quality and ensure widespread coverage [9].