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

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.

BEP/SEP and Outage Performance Analysis of -Branch Maximal-Ratio Combiner for Fading

Maximal-ratio combiner (MRC) performances in fading channels have been of interest for a long time, which can be seen by a number of papers concerning this topic. In this paper we treat bit error probability (BEP), symbol error probability (SEP) and outage probability of MRC in presence of fading. We will present fading model, probability density function (PDF), and cumulative distribution function (CDF). We will also present PDF, CDF, and outage probability of theL-branch MRC output. BEP/SEP will be evaluated for broad class of modulation types and for coherent and noncoherent types of detection. BEP/SEP and outage performances of the MRC will be evaluated for different number of branches via Monte Carlo simulations and theoretical expressions.