Free space optics (FSO) technology has demonstrated an increasingly scientific and commercial interest over the past few years. However, due to signal propagation in the atmosphere, the operation depends strongly on the atmospheric conditions and some random impairments, including turbulence and pointing error (PE) effects. In the present study, a single-input multiple-output FSO system with wavelength, spatial, or time diversity over the turbulence and non-zero boresight PE effects is thoroughly investigated. A versatile mixture composite model which accurately describes both impairments is employed for the performance evaluation. Novel mathematical expressions of the outage probability and the average bit-error rate assuming intensity modulation/direct detection and optimal combining at the reception are provided.

Over the past few years, terrestrial free space optical (FSO) communication systems have demonstrated increasing research and commercial interest. However, due the signal’s propagation path, the operation of FSO links depends strongly on atmospheric conditions and related phenomena. One such significant phenomenon is the scintillation caused by atmospheric turbulence effects; in order to address the significant performance degradation that this causes, several statistical models have been proposed. Here, turbulence-induced fading of the received optical signal is investigated through the recently presented mixture Gamma distribution, which accurately describes the irradiance fluctuations at the receiver’s input of the FSO link. Additionally, at the same time, it significantly reduces the mathematical complexity of the expressions used for the description of composite channels with turbulence along with nonzero boresight pointing error-induced fading. In order to counterbalance the performance mitigation due to these effects, serial decode-and-forward relays are employed, and the performance of the system is estimated through derived mathematical expressions.

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The performance of free-space optics links strongly depends on scintillation effects caused by the atmospheric turbulence appearance. A widely adopted way to counterbalance the expected deterioration due to scintillation is to employ cooperative and multi-hop arrangements. However, the use of multiple relays increases significantly the complexity of the mathematical models used to describe the overall performance of the system. Taking the latter into account, we approximate a generic multiple relay-assisted free-space optical configuration with a dual-hop link in order to simplify the performance analysis. To this end, we provide new mathematical derivations for the evaluation of the outage probability and the average bit error rate by assuming typical turbulence models. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.