Equal-gain combining reception over Gamma-Gamma turbulence channels with pointing errors

In this study, we investigate the performance of free-space optical communication system employing equal-gain combining receiver and operating over Gamma-Gamma turbulence channel with pointing errors. We derive the Bealieu series for the cumulative distribution function (CDF) and the probability density function (PDF) of the output signal-to-noise ratio (SNR), which is a function of the sum of the received irradiance of the individual receiver branches. We derive exact closed-form expressions for the coefficients of the Bealieu series, which makes it possible to compute the CDF and the PDF of the output SNR for different channel conditions and for arbitrary values of diversity order. To give an example of the application of the derived analytical results, the outage performance of the considered system is investigated and the effects of the pointing error are studied. Numerically evaluated and computer simulation results are given that verify the accuracy of the proposed mathematical framework.