Model for Outage Probability of Free-Space Optical Links with Spatial Diversity through Atmospheric Turbulence

Free-space optical (FSO) links offer an attractive alternative to the radio frequency channel for the purpose of transmitting data at very high rates. A major impairment in FSO links is the turbulence-induced scintillations of an optical wave. Spatial diversity, which involves the deployment of multiple laser transmitters/receivers, can be used over FSO links to reduce the turbulence-induced scintillations. In this paper, the channel of a multiple-transmitter-multiple-receiver FSO link considering the spatial correlation between the constituent sub-channels was mathematically modeled and then the joint distribution function of the channel gain coefficients was derived. Base on the joint distribution function, the model for the outage probability of a FSO link with spatial diversity was established. With Monte Carlo method, simulations for the outage probability were performed. The results show that spatial correlations have a significant influence on the outage probability, and the diversity-induced performance improvement reduces to zero as the spatial correlation coefficient increases to 1.