Approximation to the Sum of Two Correlated Gamma-Gamma Variates and its Applications in Free-Space Optical Communications

The Gamma-Gamma (ΓΓ) distribution is popularly accepted for modeling the received intensity fluctuations in the near-ground free-space optical (FSO) communication. We consider in this letter the case of dual space diversity FSO systems when the fading coefficients corresponding to the two sub-channels are correlated. In order to evaluate the receiver performance analytically, we propose to approximate the sum of correlated ΓΓ random variables by an α-μ distribution. We show that there is a good match between the performance obtained by simulated data based on the ΓΓ channel model and that obtained from analytical calculation based on the approximate α-μ model.