Secure hybrid satellite-UWOC cooperative relaying system under malicious unmanned aerial vehicle eavesdropper threat

Abstract

In this paper, the secrecy performance of a hybrid satellite-Underwater Optical Communication (UWOC) system in the presence of an Unmanned Aerial Vehicle (UAV) eavesdropper is investigated. The satellite and eavesdropper Radio Frequency (RF) links are respectively subjected to Shadowed-Rician and Nakagami-m fading distributions whereas the UWOC link experiences mixed Exponential-Gamma distribution under difference detection schemes such as heterodyne detection and Intensity Modulation with Direct Detection (IM/DD). Specifically, the equivalent Cumulative Distribution Function (CDF) closed-form expression of the concerned system is then obtained. Based on this, the analytical closed-form expressions of the system Connection Outage Probability (COP), Secrecy Outage Probability (SOP), Strictly Positive Secrecy Capacity (SPSC) and Average Secrecy Capacity (ASC) are derived. By our findings, it is found that the satellite shadowing effect, air bubbles level and temperature gradients and eavesdropper distance significantly have impact on the system secrecy performance. The result also illustrated that the heterodyne detection outperforms the IM/DD under the system and channel conditions. Finally, the accuracy of the analytical expressions is justified through Monte-Carlo simulations.