On the ergodic capacity of MIMO correlated gamma-gamma fading channels

This paper studies the ergodic capacity of multiple-input multiple-output (MIMO) correlated Gamma-Gamma (G-G) fading channels, particularly for free-space optical communications (FSO). Based on the atmospheric fading correlation analysis and by employing an approximation method for the sum of correlated (G-G) random variables (RVs), closed-form expressions for the capacity are derived for both equal gain combining (EGC) and maximal ratio combining (MRC) techniques. Numerical results confirm that channel correlation considerably degrades the performance of MIMO systems. Under a constraint of receiving area, we find that an optimal number of receiver aperture exists to achieve the best performance considering the negative impact of channel correlation. Monte-Carlo (M-C) simulations are also performed to validate the analytical results.

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