Optimal Combiners in Pre-Amplified Optical Wireless Systems under Medium-to-Strong Atmospheric Turbulence

Abstract In this work we analytically investigate optimal combiners for pre-amplified diversity receivers that operate under medium-to-strong atmospheric turbulence. We first demonstrate that the combiner performance is strongly affected by the existence of a signal-amplified spontaneous emission beat noise at the output of the photodetector. Due to the signal-dependent nature of noise, the optimal combiner can be classified as a hybrid one, of which performance is between the well-known equal-gain and maximal-ratio combiner architectures. Having established the optimal design, we further assess the proposed combiner performance over gamma-gamma and negative-exponential fading environments.