UAVs-Assisted Proactive Eavesdropping in AF Multi-Relay System

This letter studies the Unmanned Aerial Vehicles (UAVs)-assisted proactive eavesdropping in the suspicious amplify-and-forward multi-relay system, where the suspicious transmitter based on opportunistic relaying protocol selects one best suspicious relay to communicate with the suspicious destination. In addition, we assume each UAV hovers over one specific relay for the purpose of jamming or eavesdropping, which is only valid for this relay due to the limited coverage of the UAVs and the dispersion between these relays. Moreover, the UAVs used for jamming cannot implement eavesdropping concurrently due to the half-duplex constraints. Under this setup, with detailed analysis and strict proof, we find an interesting trade-off in deciding the number of UAVs used for jamming: jamming with more UAVs helps decrease the suspicious rate to facilitate the eavesdropping by remaining UAVs, but is at the cost of degrading the precondition of successful eavesdropping. Numerical results verify this trade-off and show that with simple one-dimensional search, the proposed jamming-assisted strategy achieves significant gain compared to conventional passive eavesdropping.