Free-space optical communications using all-optical relays over weak turbulence channels with pointing errors

In this paper, the outage performance of a free-space optical (FSO) communication system with parallel all-optical relays is investigated by employing the photon counting methodology. Initially, a composite channel model is considered which includes atmospheric loss, pointing error and weak atmospheric turbulence. To show the impacts of the channel state information (CSI) on system performance, either full CSI or semi-blind CSI at the relay nodes is considered. Based on the channel model, the approximate expressions of the outage probability for both full CSI relaying and semi-blind CSI relaying are derived, respectively. Numerical results substantiate that the derived expressions can provide sufficient precision for evaluating the outage performance of FSO communication systems. Moreover, for the scenario we considered, semi-blind CSI relaying can provide nearly identical performance to its full CSI counterpart.