In this paper, the secrecy performance of a dual-hop mixed radio-frequency/underwater optical wireless communication (RF/UOWC) system is investigated. The considered system consists of one single antenna source node (S) communicating with one destination node (D), considered as the legitimate receiver, through the help of one amplify-and-forward (AF) relay node R equipped with multiple antennas for reception. Specifically, the relay receives the incoming signal from S via an RF link, applies maximal-ratio combining (MRC) technique, amplifies the output combined signal with a fixed gain, and then forwards it to D via a UOWC link. The transmission protocol is performed under the eavesdroppers' attempt to overhear the RF link (i.e., S -R). We derive an exact closed-form expression for the secrecy intercept probability (IP) in terms of the Fox's H-function, or in terms of the Meijer's G-function as a particular case. The derived secrecy performance metric is evaluated in terms of various channel and system parameters, and corroborated by Monte-Carlo simulation method. Our derived analytical formulas present an efficient tool to highlight the impact of some system and channel parameters on the secrecy performance.
In this paper, the secrecy performance of a dual-hop mixed radio-frequency/underwater optical wireless communication (RF/UOWC) system is investigated. The considered system consists of one single antenna source node (S) communicating with one destination node (D), considered as the legitimate receiver, through the help of one amplify-and-forward (AF) relay node R equipped with multiple antennas for reception. Specifically, the relay receives the incoming signal from S via an RF link, applies maximal-ratio combining (MRC) technique, amplifies the output combined signal with a fixed gain, and then forwards it to D via a UOWC link. The transmission protocol is performed under the eavesdroppers' attempt to overhear the RF link (i.e., S -R). We derive an exact closed-form expression for the secrecy intercept probability (IP) in terms of the Fox's H-function, or in terms of the Meijer's G-function as a particular case. The derived secrecy performance metric is evaluated in terms of various channel and system parameters, and corroborated by Monte-Carlo simulation method. Our derived analytical formulas present an efficient tool to highlight the impact of some system and channel parameters on the secrecy performance.
In this paper, the secrecy performance of a dual-hop mixed radio-frequency/underwater optical wireless communication (RF-UOWC) system is investigated. The considered system consists of one single antenna source node (S) communicating with one destination node (D), considered as the legitimate receiver, through an amplify-and-forward relay node equipped with multiple antennas for reception. Specifically, the relay receives the incoming signal from S via an RF link, applies maximal-ratio combining technique, amplifies the output combined signal with either a fixed gain or variable gain, and then forwards it to the destination via an UOWC link. The transmission protocol is performed under the eavesdropper's attempt to overhear the RF link (i.e., S-R). We derive exact closed-form expressions for the system's average secrecy capacity and the intercept probability in terms of Meijer's G-function as well as the univariate and bivariate Fox's H-functions. A complexity analysis is also performed to analyze the evaluation time of the derived analytical formulas as well as Monte Carlo simulation method complexity. Our derived analytical formulas present an efficient tool to depict the impact of some system and channel parameters on the secrecy performance, namely, the number of relay antennas, the number of eavesdropping nodes, relay gain, fading severity of RF links, and water turbulence severity of the UOWC link.
Ensuring physical layer security is a crucial task in conventional and emerging communication systems, which are typically characterized by stringent quality of service and security requirements. This also accounts for wireless technologies in the context of the Internet of Things paradigm, which are expected to exhibit considerably increased computational complexity. Based on this, the present contribution investigates the secrecy outage performance of a dual-hop decode-and-forward (DF) mixed radio-frequency/ underwater optical wireless communication (RF/UOWC) system. Such wireless network configurations are particularly useful in efficient and demanding scenarios, such as military communications. Therefore, our analysis considers one single-antenna source node (S) communicating with one legitimate destination node (D) via a DF relay node (R) equipped with multiple antennas for reception. Particularly, the relay receives the incoming signal from S via an RF link, applies selection-combining (SC) technique, fully decodes it, re-encodes it, and then forwards it to the destination via a UOWC link. The communication is performed under the eavesdropper's attempt to intercept the S - R hop (RF side). In this context, a closed-form expression for the secrecy outage probability is derived along with a thorough asymptotic analysis in the high SNR regime, based on which the achievable diversity order is provided. The offered results provide useful insights on the impact of some key system and channel parameters on the secrecy outage performance, such as the number of eavesdroppers, the number of relay antennas, fading severity parameters of RF links, and water turbulence severity of the UOWC link. The conducted analysis shows that the secrecy outage probability is dominated only by the R-D link in the high SNR regime, regardless of the S-R parameters, such as the number of relay antennas and the average SNR at the relay branches. The offered analytic results are corroborated with respective results from computer simulations. Since these parameters are closely related with the computational complexity at the involved terminals, the offered insights are useful for the design and computationally sustainable operation of such systems.
This article investigates the secrecy performance of a dual-hop radio frequency-underwater optical wireless communication (RF-UOWC) system. Using stochastic geometry theory, the eavesdroppers are modeled as a Poisson point process distribution, and RF and UOWC links are modeled as Nakagami-mand mixture exponential-generalized gamma distributions, respectively. Firstly, we derive the statistical laws of signal-to-noise ratio for illegitimate receivers in both colluding and noncolluding scenarios and legitimate receivers when amplify-and-forward and decode-and-forward relaying strategies are employed. Subsequently, closed-form expressions for the lower bound of secrecy outage probability (SOP) are derived. Finally, analytical results are verified via Monte Carlo simulation results, and the effects of channel and system parameters on secrecy outage performance of dual-hop systems are analyzed. Numerical results demonstrate that environmental parameters, such as temperature and bubble levels, exhibit an important impact on the SOP of RF-UOWC systems.
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.
We analyze a secure two-hop mixed radio frequency (RF) and underwater wireless optical communication (UWOC) system using a fixed-gain amplify-and-forward (AF) relay. The UWOC channel is modeled using a unified mixture exponential-generalized Gamma distribution to consider the combined effects of air bubbles and temperature gradients on transmission characteristics. Both legitimate and eavesdropping RF channels are modeled using flexible α−μ distributions. Specifically, we first derive both the probability density function (PDF) and cumulative distribution function (CDF) of the received signal-to-noise ratio (SNR) of the mixed RF and UWOC system. Based on the PDF and CDF expressions, we derive the closed-form expressions for the tight lower bound of the secrecy outage probability (SOP) and the probability of non-zero secrecy capacity (PNZ), which are both expressed in terms bivariate Fox's H-function. To utilize these analytical expressions, we derive asymptotic expressions of SOP and PNZ using only elementary functions. Also, we use asymptotic expressions to determine the optimal transmitting power to maximize energy efficiency. Further, we thoroughly investigate the effect of levels of air bubbles and temperature gradients in the UWOC channel, and study nonlinear characteristics of the transmission medium and the number of multipath clusters of the RF channel on the secrecy performance. Finally, all analyses are validated using Monte Carlo simulation.
In this paper, we investigate the secrecy performance of multiuser (MU) single-input multiple-output (SIMO) mixed radio frequency (RF)/free space optical (FSO) relay network with opportunistic user scheduling and multiple eavesdropping attacks. The considered system includes multiple users, one amplify-and-froward (AF) relay, one destination and multiple eavesdroppers. The users are connected with a multi-antenna relay through RF links and the relay is connected with the destination through an FSO link. Maximal ratio combining (MRC) scheme is used at the relay node to combine the received signals at its different antennas. The RF/FSO channels are assumed to follow Nakagami-m/Gamma-Gamma fading models with considering the effect of pointing errors. In particular, we derive closed- form expressions for the exact and asymptotic outage probabilities. The asymptotic outage results are then used to obtain the optimal RF transmission power based on the dominant link between the RF and FSO links. Then, the considered system secrecy performance is investigated in the presence of multi- eavesdroppers where exact closed-form expression for the intercept probability is derived. Finally, a cooperative jamming model is proposed along with power allocation to enhance the system secrecy performance. Monte-Carlo simulations are provided to validate the achieved exact and asymptotic results.