On the Effects of Correlation on Outage Performance of FSO-Unbalanced Multibranch SC Receiver

In this letter, we study the outage performance of unbalanced multibranch selection combining receiver operating over free-space optical gamma-gamma turbulence link. The analysis is performed in the case when the position of closely placed photodiodes corresponds to the constant correlation model. Novel analytical expressions for the probability density function and cumulative distribution function of receiver signal-to-noise ratio (SNR) are derived in the infinite series form whose convergence is numerically determined. Based on these analytical results, we examine the simultaneous effects of the spatial correlation, diversity order, photodiode's diameter, and turbulence strength on outage performance. The results illustrate that spatial correlation has a strong effect on SNR gain decreasing, especially for the higher values of diversity order.