Performance Analysis of RIS-Assisted RF/FSO System for Hybrid Satellite-Terrestrial Relay Network with Decode-and-Forward Protocol

Reconfigurable intelligent surface (RIS) is an emerging signal improvement technique, which can enhance the performance of various communication technologies. Inspired by RIS technology, this paper proposes an RIS-assisted radio frequency/free space optical (RF/FSO) communication system for the hybrid satellite-terrestrial network (HSTRN). An RF source is set up on the ground to transmit electrical signals to the RIS, which further reflects the signals via an RF link to the relay satellite. The square generalized K distribution model is adopted for the RF link and the EG distribution, which is a weighted sum of the exponential and Gamma distributions, is adopted for the FSO link. The exact closed-form expressions of outage probability and average bit error rate (ABER) are derived. Furthermore, the asymptotic expressions of outage probability and ABER at high signal-to-noise ratio (SNR) are derived for engineering applications. Finally, the simulation results show that the RIS technique can significantly improve the performance of the RF/FSO communication system for HSTRN, and the performance improvement is more obvious with more reflectors.