Collaborative Beamforming for Secure UAV Swarm Communications: An End-to-End MAPPO-Based Framework Against Mobile Eavesdroppers

Unmanned aerial vehicles (UAVs) are expected to serve as core nodes for next-generation communication networks, while the broadcast nature of line-of-sight (LoS) links makes the security of transmissions a server problem, which is more prominent for a mobile eavesdropper scenario. In this paper, the security enhancement of UAV swarm communication is considered. Specifically, a UAV swarm with aerial base stations attempts to transmit confidential information to terrestrial nodes, and a mobile eavesdropper lurking nearby tries to approach better receiving points to intercept communications. For the purpose of enhancing the security of transmissions utilizing spatial freedom, a virtual antenna array is formed by the UAV swarm, and a multi-agent proximal policy optimization (MAPPO)-based approach is developed to jointly optimize the collaborative beamforming and cooperative trajectories of the UAV swarm under a maximum power constraint. The simulation results demonstrate the capability of the proposed method to direct the UAV swarm to transmit mission information directionally and validate the superiority of security performance compared to benchmarks.