Average capacity of MIMO free-space optical gamma-gamma fading channel

Atmospheric turbulence is one of the main impairments degrading the performance of free-space optical (FSO) systems. Similar to radio-frequency communications, the use of spatial diversity techniques in FSO can significantly mitigate the fading effect caused by atmospheric turbulence. In this paper, closed-form expressions for the average capacity of multiple-input-multiple-output FSO systems over strong atmospheric turbulence using Gamma-Gamma fading channel model are presented. Our analysis is carried out for both equal gain combining and maximal ratio combining diversity techniques. Numerical examples compare analytical and simulation results, quantitatively verifying the advantages of spatial diversity techniques.