LLM Meets the Sky: Heuristic Multi-Agent Reinforcement Learning for Secure Heterogeneous UAV Networks

--This work tackles the physical layer security (PLS) problem of maximizing the secrecy rate in heterogeneous UA V networks (HetUA VNs) under propulsion energy constraints. Unlike prior studies that assume uniform UA V capabilities or overlook energy-security trade-offs, we consider a realistic scenario where UA Vs with diverse payloads and computation resources collaborate to serve ground terminals in the presence of eavesdroppers. T o manage the complex coupling between UA V motion and communication, we propose a hierarchical optimization framework. The inner layer uses a semidefinite relaxation (SDR)-based S2DC algorithm combining penalty functions and difference-of-convex (d.c.) programming to solve the secrecy precoding problem with fixed UA V positions. The outer layer introduces a Large Language Model (LLM)-guided heuristic multi-agent reinforcement learning approach (LLM-HeMARL) for trajectory optimization. LLM-HeMARL efficiently incorporates expert heuristics policy generated by the LLM, enabling UA Vs to learn energy-aware, security-driven trajectories without the inference overhead of real-time LLM calls. The simulation results show that our method outperforms existing baselines in secrecy rate and energy efficiency, with consistent robustness across varying UA V swarm sizes and random seeds. ITH the rapid advancement of 6G technology, unmanned aerial vehicles (UA Vs) have increasingly become a critical component of modern communication infrastructure, owing to their high mobility, strong scalability, and the provision of reliable line-of-sight (LoS) links [1], [2]. However, the broadcast nature of wireless channels over LoS links makes UA V communications more susceptible to eavesdropping and jamming attacks compared to traditional terrestrial networks, which poses significant security and privacy threats.