Abstract This work investigates physical-layer security of underwater wireless optical communication systems under covert non-line-of-sight (NLOS) eavesdropping caused by scattered photons. A first-order single-scattering model is developed for the near-transmitter NLOS eavesdropping link by incorporating seawater absorption, scattering, beam divergence, receiver field of view, and Eve’s geometry. Turbulence-induced fading on the legitimate line-of-sight link is also considered. Based on photon-counting detection, secrecy capacity, interception probability, and secrecy outage probability are analyzed. Results show that stronger scattering enlarges the high-risk region of NLOS information leakage, while stronger Bob-link turbulence degrades the secrecy performance of the system. A comparison with multiple-scattering Monte Carlo photon tracing for Jerlov IB and Jerlov II waters shows close agreement in the dominant spatial photon-count distribution.
Abstract This work investigates physical-layer security of underwater wireless optical communication systems under covert non-line-of-sight (NLOS) eavesdropping caused by scattered photons. A first-order single-scattering model is developed for the near-transmitter NLOS eavesdropping link by incorporating seawater absorption, scattering, beam divergence, receiver field of view, and Eve’s geometry. Turbulence-induced fading on the legitimate line-of-sight link is also considered. Based on photon-counting detection, secrecy capacity, interception probability, and secrecy outage probability are analyzed. Results show that stronger scattering enlarges the high-risk region of NLOS information leakage, while stronger Bob-link turbulence degrades the secrecy performance of the system. A comparison with multiple-scattering Monte Carlo photon tracing for Jerlov IB and Jerlov II waters shows close agreement in the dominant spatial photon-count distribution.
Underwater wireless optical communication (UWOC) possesses significant advantages, such as high bandwidth, low latency, and low power consumption, making it a key technology for building information networks in marine environments. However, due to the scattering effect of seawater, some photons carrying information inevitably scatter out of their predetermined paths, leading to the possibility for information leakage. Therefore, we propose a physical-layer security analysis model for UWOC systems based on the wiretap channel model. The model evaluates the security of the communication system by calculating the capacity difference between the legitimate channel and the eavesdropping channel in the UWOC system. Specifically, the model first constructs the three-dimensional intensity distribution of scattered photons in the underwater channel via Monte Carlo simulations and experimental measurements. Then, it calculates the capacities of both the legitimate and eavesdropping channels based on the decoding results. Finally, the three-dimensional distribution of secrecy capacity is derived to assess the security of the communication system. In this work this model is used to analyze the security of the UWOC system in clear seawater environments. The results show that the secrecy capacity of the system is zero within a certain range near the transmission path, demonstrating that scattered photons can cause information leakage. We recommend that, in practical applications, monitoring the non-signal transmission area near the transmitter is essential to ensure communication security. This research provides a solution for analyzing the quantitative security of UWOC, which can strongly support the design of UWOC systems and encoding/decoding schemes.
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.
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.
This paper investigates the secure communication over Non-Line-of-Sight (NLOS) Ultraviolet (UV) links suffering from turbulence-induced fading, where the transmitter and the receiver or eavesdropper cone axes lie in the same plane or different planes and can be pointed in arbitrary directions. The closed-form expressions of the Average Secrecy Capacity (ASC), the Secrecy Outage Probability (SOP) and the Probability of Positive Secrecy Capacity (PPSC) are derived to evaluate the secrecy performance. Finally, simulation results are provided to verify the accuracy of our derivations and show the effect of transmission power and elevation angle on the ASC, SOP and PPSC.
In this study, physical layer security (PLS) in a dual-hop underwater optical wireless communication (UOWC)-radio frequency (RF) network under the intruding attempts of multiple eavesdroppers via RF links is considered. An intermediate decode-and-forward (DF) relay node between an underwater source and a destination transforms the optical signal into an electrical form and forwards it to the destination node with the help of harvested energy by the relay from an integrated power beacon within the system. The source-to-relay link, i.e., a UOWC link, is assumed to follow a mixture of exponential generalized Gamma turbulence with pointing error impairments whereas all the remaining links, i.e., RF links, are assumed to undergo κ-μ shadowed fading. Here, two eavesdropping scenarios are considered depending on the types of intruders, i.e., colluding (Scenario-I) and non-colluding (Scenario-II) eavesdropping operations. The analytical expressions of secrecy outage probability (SOP), probability of strictly positive secrecy capacity (SPSC), and effective secrecy throughput (EST) are derived for each scenario. Furthermore, the impacts of UOWC and RF channel parameters as well as detection techniques on secrecy capacity are demonstrated. A comparative study between two scenarios demonstrates that the collusion between the eavesdroppers imposes the most harmful threat on secrecy throughput but a better secrecy level can be attained by adopting diversity at the destination and power beacon nodes along with heterodyne detection rather than intensity modulation and direct detection technique. Finally, all the derived expressions are verified with the numerical results.