In this work, the effective secrecy throughput (EST) which explicitly captures both the reliability and secrecy features of wiretap channels for an underwater wireless optical communication (UWOC) system has been optimized by considering the generalized transmit laser selection (GTLS) scheme. Specifically, the instantaneous channel state information (CSI) of the main channel and eavesdropper's channel is assumed to be unavailable at the transmitter, which is more practical for the underwater application. The fading of salinity induced oceanic turbulence channels is described by the Weibull distribution considering angular pointing error. The GTLS scheme is first introduced into the UWOC eavesdropping system to improve the quality of the main channel. Based on these models, the analytical closed-form expression of the EST with a constraint on the maximum allowed secrecy outage probability (SOP) is mathematically derived in terms of Meijer's G function and Gauss hypergeometric function. Then, an optimization problem with the objective of maximizing the constrained EST of the proposed UWOC system while ensuring wiretap code rate constraints are formulated. To solve this problem, a whale optimization algorithm (WOA) based wiretap code rates optimization method is effectively developed to acquire the maximum constrained EST, which is validated by the exhaustive search (ES) method. Simulation results suggest that the maximum constrained EST of this UWOC system can be significantly improved by the GTLS scheme. Besides, the maximum allowed SOP has a pronounced impact on the maximum constrained EST. The presented results could offer valuable insights into the physical layer security (PLS) performance enhancement of UWOC systems.
In this work, the effective secrecy throughput (EST) which explicitly captures both the reliability and secrecy features of wiretap channels for an underwater wireless optical communication (UWOC) system has been optimized by considering the generalized transmit laser selection (GTLS) scheme. Specifically, the instantaneous channel state information (CSI) of the main channel and eavesdropper's channel is assumed to be unavailable at the transmitter, which is more practical for the underwater application. The fading of salinity induced oceanic turbulence channels is described by the Weibull distribution considering angular pointing error. The GTLS scheme is first introduced into the UWOC eavesdropping system to improve the quality of the main channel. Based on these models, the analytical closed-form expression of the EST with a constraint on the maximum allowed secrecy outage probability (SOP) is mathematically derived in terms of Meijer's G function and Gauss hypergeometric function. Then, an optimization problem with the objective of maximizing the constrained EST of the proposed UWOC system while ensuring wiretap code rate constraints are formulated. To solve this problem, a whale optimization algorithm (WOA) based wiretap code rates optimization method is effectively developed to acquire the maximum constrained EST, which is validated by the exhaustive search (ES) method. Simulation results suggest that the maximum constrained EST of this UWOC system can be significantly improved by the GTLS scheme. Besides, the maximum allowed SOP has a pronounced impact on the maximum constrained EST. The presented results could offer valuable insights into the physical layer security (PLS) performance enhancement of UWOC systems.
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.
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.
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.
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.
With the expansion of human activities into the ocean, there is an urgent need for information transmission technology with higher data rates and more security. On the other hand, satellite communication plays an important role in the maritime area, but is also vulnerable to eavesdropping because of its broadcast nature. Therefore, in this study, the physical-layer security for a hybrid satellite and underwater wireless optical communication (UWOC) system is considered. Specifically, a satellite source first broadcasts information to an overwater relay via an RF link, and then the relay converts the electrical signal to an optical one and transmits it to an underwater destination via a UWOC link, while an eavesdropper is overhearing this transmission. We derived the closed-form expressions for several system performance metrics, i.e., secrecy outage probability (SOP), and average secrecy capacity (ASC). Finally, Monte-Carlo simulations verify the accuracy of those results.
In this paper, we investigate the physical layer security of a vertical relay-assisted underwater wireless optical communication system with simultaneous lightwave information and power transfer and artificial noise to enhance both security and energy sustainability. The relay node is equipped with an energy harvesting device, using the harvested energy to transmit the confidential information and artificial noise to the user and eavesdropper. Taking into account path loss, turbulent fading, pointing error, link interruption, and solar noise, we derive the reliability outage probability, secrecy outage probability, and effective secrecy throughput (EST) and analyze the effects of water types, turbulence strength, pointing errors, and link interruption on secrecy performance. Based on this, to further improve the secrecy performance, we propose an EST optimization problem considering the power splitting ratio, including the ratio of energy harvesting and information decoding, as well as the ratio of artificial noise and confidential information. Considering the complexity and coupling of the objective function, we use an alternating optimization (AO) algorithm to achieve EST maximization. Monte Carlo simulations are conducted to verify our derived expressions, and simulation results demonstrate that the power splitting ratio obtained by AO can improve the EST effectively.