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The free-space optical communication systems attract significant research and commercial interest the last few years, due to their high performance and reliability characteristics along with their, relatively, low installation and operational cost. Moreover, due to the fact that these systems are using the atmosphere as propagation path, their performance is varying according to its characteristics. Here, we present the performance analysis of a serially relayed radio-on-free-space-optical (RoFSO) communication system which employs the orthogonal frequency division multiplexing technique, with a quadrature amplitude modulation scheme, over atmospheric turbulence channels modelled by either the Gamma-Gamma or the Gamma distribution model. For this RoFSO communication link, we derive closed-form mathematical expressions for the estimation of its average bit error rate and outage probability, taking into account the relays' number, the atmospheric turbulence and the pointing errors effect. Furthermore, for realistic parameter values, numerical results are presented using the derived mathematical expressions, which are verified through the corresponding numerical simulations.

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Radio-on-Free-Space Optical systems constitute a very attractive option for interconnecting central base stations with remote antenna units. Nonetheless, the optical signal propagation through the atmosphere is tremendously affected by turbulence-and misalignment-induced fading. In the present study, we investigate the transmission of code division multiple access signals over a free-space optical (FSO) link. The atmospheric turbulence is modeled by the M (Malaga) distribution, which acts as a unifying statistical model encompassing all the well-known distributions that have been proposed in the FSO area. In addition, nonzero boresight pointing errors (PEs) are employed, which are described by an accurate approximation of the Beckmann distribution. Novel mathematical expressions are extracted regarding the average bit error rate and the outage probability of the forward and the reverse link. Moreover, appropriate numerical results are depicted for various turbulence and PE scenarios, along with their associated corroborative outcomes.

In this paper, we carry out a performance analysis of a full-duplex (FD) relaying system consisting of parallel hybrid radio frequency (RF)/free-space optical (FSO) communication links. The RF links are hampered by the residual self-interference (RSI), due to the FD relaying operation, along with the in-phase and quadrature-phase imbalance (IQI) effect, due to imperfections at the RF nodes' front-ends. The parallel FSO links, of the dual-hop configuration, are influenced by the joint effects of atmospheric turbulence and pointing errors. The performance of the dual-hop FD system with parallel hybrid RF/FSO links, operating under a hard-switching scheme, is evaluated in terms of the outage probability. Analytical closed-form expressions are derived for both RF and FSO subsystems as well as for the overall dual-hop hybrid system. The presented numerical results show the significant performance gains obtained by the exploitation of parallel RF/FSO links in an FD relaying channel under various operating conditions. Finally, the derived analytical results are verified by Monte Carlo simulations.