Performance Analysis of a Hybrid FSO/RF/THz Relay Communication System

A dual-hop hybrid free-space optical/radio frequency (FSO/RF) relay system is considered an effective solution for increasing the capacity and coverage of wireless communication systems between last-kilometer access networks and backbone networks. However, the transmission performance of FSO links is greatly affected by atmospheric turbulence, pointing errors, fog, and snow. The RF access network has a low rate and high delay. To ensure communication quality, a hybrid FSO/RF/terahertz (THz) relay system was designed. Decode-and-forward relaying was selected and hybrid FSO/RF communication based on an adaptive-combining scheme was considered before the relay nodes. THz links were used after the relay nodes to reach the users. Using the statistical characteristics of the different obtained links, expressions for the outage probability and average bit error rate of the system were derived. The effects of different parameters on the performance of hybrid FSO/RF/THz relay systems were studied, and the first-hop adaptive-combining scheme was compared with the single-threshold switching scheme and single-link FSO system. The analysis results indicated that the hybrid FSO/RF/THz relay system provided better outage and error performance using an adaptive-combining scheme. It improved the system communication rate while considering the communication reliability.