Error Performance of Relay-Assisted Free-Space Optical Communication Links Over Atmospheric Turbulence Channels

Free-space optical (FSO) communication has regained substantial research interests in the recent decade and is well reckoned as a viable alternative which is highly complementary/integrable with existing radio frequency (RF) solutions, such as the 5G wireless networks. Unpredictable weather conditions severely impair the link availability and performance of the FSO system. The presence of atmospheric loss and turbulence-induced optical scintillation within the communication channel causes attenuation and random fluctuation of the received optical signals, thereby limiting the link distance and impairing the error performance. Multi-hop relaying technique can be adopted in the FSO system for improving the channel gain and mitigating the turbulence-induced channel fading. In this paper, we examine the bit error rate (BER) performances of FSO systems operating in the single-input single-output (SISO) and multi-hop relay-based configurations. The BER analysis is carried out using MATLAB simulation, whereby weather-dependent parameters and turbulence strength values for different weather scenarios such as clear air, light fog, and haze are considered here. Next, the aperture-averaging phenomenon caused by the receiver aperture dimension is jointly investigated with the relay-assisted multi-hop relaying technique. From our study, it is evident that the SISO FSO configuration is vulnerable to system outage, which can be effectively mitigated with the introduction of relay terminals. Our findings conclude that the relay-assisted multi-hop FSO system with aperture averaging is a feasible approach toward reducing the BER performance with minimum power requirement.