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This work deals with the secrecy performance analysis of a dual-hop RF-FSO DF relaying network composed of a source, a relay, a destination, and an eavesdropper. We assume the eavesdropper is located close to the destination and overhears the relay’s transmitted optical signal. The RF and FSO links undergo ( $\alpha -\kappa -\mu $ )-shadowed fading and unified Málaga turbulence with pointing error. The secrecy performance of the mixed system is studied by deriving closed-form analytical expressions of secure outage probability (SOP), strictly positive secrecy capacity (SPSC), and intercept probability (IP). Besides, we also derive the asymptotic SOP, SPSC, and IP upon utilizing the unfolding of Meijer’s $G$ function where the electrical SNR of the FSO link tends to infinity. Finally, the Monte-Carlo simulation is performed to corroborate the analytical expressions. Our results illustrate that fading, shadowing, detection techniques (i.e. heterodyne detection (HD) and intensity modulation and direct detection (IM/DD)), atmospheric turbulence, and pointing error significantly affect the secrecy performance. In addition, better performance is obtained exploiting the HD technique at the destination relative to IM/DD technique.

In this paper, we analyze a combined terrestrial-underwater optical communication link for providing high-speed optical connectivity between onshore and submerge systems. For this purpose, different transmission signaling schemes were employed to obtain performance results in terms of average bit error rate (ABER). In this sense, from the starting point of a known conditional bit-errorrate (CBER) in the absence of turbulence, the behavior of the entire system is obtained by applying an amplify-and-forward (AF) based dual-hop system: The first link is a terrestrial free-space optical (FSO) system assuming a Málaga distributed turbulence and, the second one, is an underwater FSO system with a Weibull channel model. To obtain performance results, a semi-analytical simulation procedure is applied, using a hyper-exponential fitting technique previously proposed by the authors and leading to BER closed-form expressions and high-accuracy numerical results. This research was funded by Junta de Andalucía (research group “Communications Engineering (TIC-0102)”). : The authors want to thank to the Spanish Ministerio de Ciencia, Innovación y Universidades (proyect PID2019-107792GB-I00) for supporting this work. Partial funding for open access charge: Universidad de Málaga

Performance analysis is presented for a decode-and-forward protocol based mixed radio-frequency (RF) and free-space optical (FSO) dual-hop transmission system with digital coherent detection. The RF path is modeled by Beaulieu-Xie fading, while the FSO hop is characterised by the Malaga ( $\mathcal {M}$ ) distributed turbulence with pointing errors. We first derive novel and exact analytical expressions for the cumulative distribution function (CDF), the probability density function and the moment generating function (MGF) of the overall signal-to-noise ratio by means of Meijer’s G function, followed by the accurate infinite series expressions of the performance criterions, such as the outage probability, the average bit-error rate (BER) and the ergodic capacity (average channel capacity). Asymptotic analysis for the CDF, the MGF, the outage probability, the average BER, and the ergodic capacity is also provided. Monte Carlo simulations are performed to verify these derived expressions.