In this Letter we propose a closed-form expression for the average bit error rate of intensity modulation/direct detection free-space optical systems employing dual-branch equal-gain combining and operating over turbulence channels. To offer a realistic error performance of the considered system we assume that both branches undergo independent but not necessarily identically distributed gamma–gamma fading. Our newly developed formula is obtained in terms of the bivariate H-Fox function, which can be readily evaluated based on its two-fold Mellin–Barnes representation. Numerically evaluated and computer simulation results are presented that verify the accuracy of the proposed mathematical analysis.
© 2013 Optical Society of America
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