Performance Analysis of Spatial Diversity-Based Free Space Optical Communications Systems for Various Atmospheric Turbulence Models with Pointing Errors

Abstract This paper conducts a comprehensive analysis of the performance characteristics of Free Space Optical (FSO) communications systems operating across diverse channel conditions. The mathematical procedure for performance evaluation of single-input single-output (SISO) FSO is reviewed for versatile link position and direction, which facilitate for the beginner researchers starting the study of the physical FSO communications links from one article. Furthermore, We study a receiver-diversity arrangement consisting of a central aperture surrounded by a ring of apertures. Depending on this arrangement, the multiple-input multiple-output FSO performance is elaborated under various atmospheric turbulence and pointing error channel models for coherent and subcarrier intensity modulation systems. This MIMO-FSO arrangement can be used in the future to improve the system performance and reliability. Leveraging the α-µ distribution and the proposed receiver configuration, we develop approximate analytical formulations for both the probability density function (PDF) of the instantaneous signal-to-noise ratio (SNR) and its corresponding cumulative distribution function (CDF). In the case of MIMO links with turbulence that is independent across apertures and pointing jitter common to all apertures, the outage probability and the ergodic capacity of the maximum ratio combining (MRC) and equal gain combining (EGC) are also formulated for MIMO-FSO systems in terms of the Fox-H 1 function and other simple functions. The performance gaps between different combining and modulation techniques are illustrated.