Average capacity of MIMO/FSO systems with equal gain combining over log-normal channels

Atmospheric turbulence is one of the major challenges in free-space optical (FSO) systems. The use of multiple receivers and multiple transmitters provides an effective approach to mitigate the fading effect caused by the atmospheric turbulence. In this paper we extract the closed form expression for the average capacity of the multiple-input multiple-output (MIMO) FSO channel. Equal gain combining spatial diversity technique in the log-normal turbulence regime is considered. Our analytical derivations are constructed based on the Wilkilson approximation to the sum of log-normal random variables. The derived capacity expressions quantify the advantages of spatial diversity techniques.