On the Performance of Reconfigurable Intelligent Surface in Cooperative Decode-and-Forward Relaying for Hybrid RF/FSO Systems

Reconfigurable intelligent surface (RIS) has been suggested as a promising solution to prevent wireless communication systems from transmission blockage. In this paper, the performance of reconfigurable intelligent surface in cooperative decode-and-forward relaying for hybrid radio frequency (RF)/free space optical (FSO) system is evaluated where parallel transmission of information occurs on the system downlink. In this network, the RF links in the system are assumed to follow Nakagami-m distributions while the FSO link is subjected to Gamma-Gamma distribution. Thus, the exact closed-form expressions of the system outage probability and average bit error rate are obtained to quantify the system performance. The accuracy of these expressions is justified by Monte-Carlo simulations. Also, to get more physical insight from the derived outage probability expression, the asymptotic outage probability under the condition of higher signal-to-noise ratio (SNR) is provided. In addition, the results illustrate that the system and channel parameters significantly affect the performance of the concerned system. Furthermore, the results show that RIS-hybrid downlink system offers better performance than hybrid downlink system without RIS. Under the RIS system, the results demonstrate that RIS-hybrid downlink system outperforms RIS-FSO downlink system.