Physical-Layer Security for Multi-antenna Satellite-UWOC Systems in the Presence of Spatially Random Locations

In this work, the physical-layer security for a maritime relay-assisted hybrid satellite and underwater wireless optical communication system consisting of a satellite source, a maritime relay (R), an underwater destination, and an eavesdropper (E) is investigated. In addition, both R and E are with multiple antennas and randomly located. In real application scenarios, E may be different carriers, i.e., an aircraft in the air or a ship on the sea, with various scopes of activity. Therefore, two different randomly located scenarios are considered, such as randomly distributed in a three dimensional space and a two dimensional plane. Furthermore, the beam-angle information of the source is assumed to be unavailable to E, and E may be located outside of the beam coverage area. Therefore, the beam coverage probability (BCP) for E is also presented. Employing the stochastic geometry theory and the maximum ratio combining scheme, the analytical and asymptotic expressions of secrecy outage probability (SOP) are obtained. In addition, the overall system SOP is defined and presented by taking both SOP and BCP into account. Finally, Monte-Carlo simulations verify the accuracy of our analysis.