In response to the dearth of radio frequency (RF) equivalents, there has been a recent surge in interest in optical wireless communication in underwater environments. To ensure a strong line-of-sight (LOS) connection, the intelligent reflecting surface (IRS) is installed to create a virtual LOS. Then, the first part of this study looks into the security of underwater optical wireless communication (UOWC) in relation to a number of real-world phenomena, including oceanic propagation loss, oceanic turbulence, and IRS-induced geometric loss. Then, a wiretap channel with three authorized users - a reputable broadcaster named Alice (the submarine), a law-abiding user named Bob, and an eavesdropper named Eve - is examined over turbulent channels that exhibit the Log-normal distribution. Furthermore, our study derives the closed-form formulas for the secrecy performance measures, secrecy outage probability, and secrecy throughput. Finally, the numerical results show how the impact of oceanic turbulence-induced fading and distance between Bob’s and Eve’s positions on the secrecy system performance.
In response to the dearth of radio frequency (RF) equivalents, there has been a recent surge in interest in optical wireless communication in underwater environments. To ensure a strong line-of-sight (LOS) connection, the intelligent reflecting surface (IRS) is installed to create a virtual LOS. Then, the first part of this study looks into the security of underwater optical wireless communication (UOWC) in relation to a number of real-world phenomena, including oceanic propagation loss, oceanic turbulence, and IRS-induced geometric loss. Then, a wiretap channel with three authorized users - a reputable broadcaster named Alice (the submarine), a law-abiding user named Bob, and an eavesdropper named Eve - is examined over turbulent channels that exhibit the Log-normal distribution. Furthermore, our study derives the closed-form formulas for the secrecy performance measures, secrecy outage probability, and secrecy throughput. Finally, the numerical results show how the impact of oceanic turbulence-induced fading and distance between Bob’s and Eve’s positions on the secrecy system performance.
The advantages of physical layer security (PLS) have led researchers to apply this in various communication scenarios, such as radio frequency (RF) communication, free space optical (FSO) communication, and underwater optical wireless communication (UOWC). This paper analyzes the PLS, specifically the effective secrecy throughput (EST) over the mixture exponential generalized gamma (mEGG) UOWC channel link in the presence of a passive eavesdropper. To achieve this goal, firstly the closed-form expression of the secure outage probability (SOP) of the system is derived, and using that SOP expression, the final EST expression is found considering the underwater turbulence (air bubble and temperature gradient) as well as two different detection scenarios (heterodyne detection (HDD) & intensity modulation/direct detection(IM/DD)) in terms of Meijer-G functions. Moreover, the average secrecy capacity (ASC) of such a scenario is also exploited in this work. Finally, the expressions are verified through Monte-Carlo simulation.
To cope with the scarcity of radio frequency (RF) counterparts, free-space optics (FSO) based on satellite communications technologies have recently gained a lot of interest. Firstly, this investigates the security of space-to-ground intensity modulation/direct detection FSO satellite communications in various effects from the physical world, such as propagation loss, beam misalignment, cloud attenuation, and fading caused by atmospheric turbulence. Next, A wiretap channel composed of a genuine broadcaster Alice (i.e., the satellite), a legitimate user Bob, and an eavesdropper Eve is considered over turbulent channels characterized by the Fisher-Snedecor F distribution. In addition, the closed-form expressions of the secrecy performance metrics, including average secrecy capacity, secrecy outage probability, and strictly positive secrecy capacity, are derived in our study. Finally, the numerical findings indicate that the satellite altitude of 600 km should be used to achieve a secrecy outage of roughly 50% for the whole turbulence regime. In addition, high levels of cloud liquid water content (CLWC) could improve the secrecy performance as it is shown that, the average secrecy capacity increases by about 12% when the CLWC increases from 1mg/m3 to 2mg/m3.
With the rapid evolution of communication technologies, high-speed optical wireless applications under the water surface as a replacement or complementary to the conventional radio frequency (RF) and acoustic technologies are attracting significant attention from the researchers. Since underwater turbulence (UWT) is an inevitable impediment for a long distance underwater optical wireless communication (UOWC) link, mixed RF-UOWC is being considered as a more feasible solution by the research community. This article deals with the secrecy performance of a variable gain relay-based mixed dual-hop RF-UOWC framework under the intercepting attempt of a potential eavesdropper. The RF link undergoes Generalized Gamma (GG) fading distribution, whereas the UOWC link is subjected to mixture Exponential Generalized Gamma (mEGG) distribution. The eavesdropper is capable of wiretapping via a RF link that also experiences the GG fading. The secrecy analysis incorporates the derivations of closed-form expressions for strictly positive secrecy capacity, average secrecy capacity, and exact as well as lower bound of secrecy outage probability in terms of univariate and bivariate Meijer's G and Fox's H functions. Based on these expressions, impacts of heterodyne and intensity modulation/direct detection techniques along with weak, moderate, and severe UWT conditions due to air bubbles, temperature, and salinity gradients are quantified. To the best of authors' knowledge, the proposed model is the first of its kind that addresses the secrecy analysis of a temperature gradient RF-UOWC system along with air bubbles, as opposed to the existing models that considered thermally uniform scenarios only. Finally, the derived expressions are verified via Monte-Carlo simulations.
Underwater wireless optical communication (UWOC) has emerged as a promising solution for short-range high-speed underwater data transmission in recent years. For what is believed to be the first time, this work presents a comprehensive secrecy performance analysis of a downlink non-orthogonal multiple access (NOMA)-UWOC system over the composite vertically stratified Weibull-generalized gamma (WGG) oceanic fading channel, in which the impacts of path loss, underwater turbulence, pointing errors, and angle-of-arrival fluctuations are considered. Specifically, the closed-form expressions for the probability density function (PDF) and cumulative distribution function (CDF) of the vertically stratified WGG fading channel coefficient are derived analytically. Then, on the basis of these derivations, analytical frameworks for the key secrecy performance metrics, including secrecy outage probability, strictly positive secrecy capacity, and effective secrecy throughput, are obtained, taking into account the residual interference from successive interference cancellation (SIC), which are validated through Monte Carlo simulations. Finally, the effects of the number of layers, the thermohaline gradient and air bubbles, the residual power factor of imperfect SIC, the transceiver misalignment, and the angle-of-arrival deviation are investigated on this UWOC system. The presented results give valuable insights into the practical aspects of deployment of UWOC networks.
The analysis of physical layer security aspects in underwater optical wireless communication (UOWC) systems has attracted considerable attention in recent years due to the increasing need to transmit large and secure amounts of data. This article, therefore, performs a careful investigation of the secrecy outage probability (SOP) of UOWC systems over Weibull oceanic turbulence channels with angular misalignment errors that are affected by absorption and scattering. The SOP performance is then evaluated under the intercepting attempt of underwater eavesdroppers or unauthorized drones that search for an opportunity to capture radiated power with the goal of decreasing the channel capacity of the main channel or increasing the probability of an unsecured communication. In this way, novel approximate closed-form solutions are derived for the SOP, which are corroborated by Monte Carlo simulations in different real scenarios such as clear ocean and coastal waters that are modeled by a determined chlorophyll-a concentration. The results show that the effect of scattering plays a crucial role in determining which kind of water is more secure in terms of SOP performance for different severity of pointing errors.
Although underwater wireless optical communication (UWOC) receives much interest lately, security issues associated with it get little attention. In this work, it is the first attempt to investigate the physical layer security (PLS) performance of the vertical UWOC system with perfect and imperfect channel state information (CSI). Specifically speaking, the communication between two legitimate peers in the presence of an external eavesdropper is studied from the information-theoretic security perspective. Assuming that turbulence-induced fading over the vertical UWOC links is respectively subject to cascaded lognormal (LN) and Gamma-Gamma (GG) distributions for weak and moderate/strong turbulence conditions, and the angular pointing error is randomized by the Beckmann distribution, the composite cascaded statistical fading models are derived with the comprehensive effects of path loss, underwater turbulence, angular pointing errors, and channel estimation error. On the basis of these models, analysis frameworks of the probability of strictly positive secrecy capacity (SPSC), secrecy outage probability (SOP), and average secrecy capacity (ASC) are further obtained for this UWOC system, which are confirmed by Monte Carlo (MC) simulations. Furthermore, the effects including the number of layers, the level of channel estimation error, the link distance, the location of the eavesdropper, the quality of the main and eavesdropping channels on this system are analyzed for different water conditions. The presented results give valuable insights into the practical aspects of deployment of UWOC networks.