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Journal of the Optical Society of America A

Secrecy performance analysis of NOMA-UWOC systems over a vertically stratified WGG oceanic turbulence channel

Qian Hu, Ping Wang, Shuang Li, Xiaorui Qiao, Yong Gao, Weihan Hao

Published Apr 27, 2026• 0 citations
Publisher

Abstract

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.

DOI
10.1364/josaa.589421

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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.
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 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.
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.
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.
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 secrecy performance is analyzed for a two-hop mixed radio frequency (RF)/underwater wireless optical communication (UWOC) system using a decode-and-forward (DF) relay. All RF and UWOC links are modeled by the$\alpha -\mu $and exponential-generalized Gamma distributions, respectively. We first derive the expressions of a lower bound of secrecy outage probability in closed-form, and these expressions are used to derive asymptotic expressions in simple functions at high signal-to-noise ratio. Moreover, based on the asymptotic expressions, we can numerically determine a suboptimal transmit power for a wide variety of RF and UWOC channel conditions. All analyses are validated using Monte Carlo simulation.