Secrecy Analysis of Decode-and-Forward Relay Based Heterogeneous Terrestrial RF - Underwater Acoustic System

This study examines how well a heterogeneous dual-hop terrestrial radio frequency and underwater acoustic downlink system maintain confidentiality. It includes an RF source, an intermediate decode-and-forward relay, an underwater multi-hydrophone destination, and a nearby eavesdropper. Eavesdropper overhears underwater acoustic signal transmitted by the relay. RF and underwater acoustic links undergo Nakagami-m and Rayleigh fading, respectively. Due to the propagation delay of underwater scenario, both destination and eavesdropper links are associated with outdated channel state information which also employs maximal-ratio combining. The closed form expressions of secrecy outage probability, strictly positive secrecy capacity, and intercept probability are derived. Monte-Carlo simulations are obtained to certify the analytical expressions.