Performance analysis for free-space optical communications using parallel all-optical relays over composite channels

In the last 2 years, all-optical relaying techniques for free-space optical (FSO) communications have drawn considerable attention. In this study, the outage performance of an FSO communication system with parallel all-optical relays is investigated. A composite channel is established, which includes atmospheric loss, pointing error and atmospheric turbulence. To show the impact of the channel state information (CSI) on system performance, either full CSI or semi-blind CSI at the relay nodes is considered. After that, the theoretical expressions of the outage probabilities for different scenarios are derived. Numerical results show that the derived expressions are quite accurate to evaluate the system performance. Moreover, the derived results demonstrate that the systems with semi-blind CSI relaying can provide comparable performance to systems with full CSI relaying, and also indicate that the performance over strong turbulence channels with clear weather outperforms that over weak turbulence channels with light fog.