Channel capacity enhancement of RIS-assisted FSO communication system for high-speed trains access connectivity

Abstract

The rising utilization and technological progress of high-speed train (HST) systems, combined with the requirement for uninterrupted and dependable internet connectivity, have made it essential to provide broadband internet services onboard HSTs. Free space optics communication (FSOC) is a promising technology for providing broadband Internet access to HSTs. Technological innovations such as reconfigurable intelligent surfaces (RISs) are being explored to enhance the performance of FSOC systems. This study proposes an Optimal Rate Adaptation (ORA)-based RIS-assisted FSOC system. We investigated the statistical properties of RIS-assisted and direct FSO channels under moderate to strong turbulence conditions with and without pointing errors. Considering the aforementioned fading conditions, we subsequently formulated the average signal-to-noise ratio and the average channel capacity of the system using the ORA technique. The results show that the proposed RIS-assisted FSOC system achieves an average spectral efficiency (ASE) of 4 bits/sec/Hz at 24 dB average SNR for a 500 m link length. © 2025 Elsevier B.V.