Diversity combining in FSO systems in presence of non-Gaussian noise

Free-space optics (FSO) communication has received much attention in recent years as a cost-effective, license-free, and wide-bandwidth access technique for high data rate applications. The performance of FSO communication, however, severely suffers from turbulence caused by atmospheric conditions. Multiple photodetectors can be placed at the receiver to mitigate the turbulence and exploit the advantages of spatial diversity combining. In this paper, we analyze the bit error rate (BER) performance of an FSO communication system employing binary phase-shift keying with additive non-Gaussian noise over negative exponential distributed atmospheric turbulence and spatial diversity at the receiver. The Laplace distribution is used to model the non-Gaussian impulsive noise. We consider the case when perfect channel state information is available at the receiver for implementation of coherent detection. Analytical expressions for the BER of a single channel receiver as well as that of a diversity combining receiver using selection combining, dual-diversity equal-gain combining, and maximal-ratio combining are derived. The derived analytical expressions are verified by simulation results.