Physical-Layer Security Enhancement for UAV Downlink Communication Using Joint Precoding and Artificial Noise Design in Generalized Spatial Directional Modulation

This paper proposes a novel joint precoding and artificial noise design framework for generalized spatial directional modulation (AN-GSDM) in unmanned aerial vehicle (UAV) communications, aimed at enhancing the physical-layer security of downlink UAV communication systems. The key innovation lies in the dynamic co-optimization of multi-beam control and artificial noise (AN) power allocation under mobility constraints, enabling real-time adaptation to varying channel conditions. This approach jointly optimizes the precoding matrix and power-control factor, facilitating the effective management of multi-beams and AN to maximize the secrecy rate. The secrecy rate expression is derived, and the corresponding joint optimization problem is formulated. Due to the non-convex nature of the problem and the lack of a closed-form solution, an alternating iterative algorithm is proposed. This algorithm alternates between optimizing the precoding matrix using gradient descent and deriving a suboptimal closed-form solution for the power-control factor. Simulation results confirm that the proposed algorithm significantly enhances security by maximizing the secrecy rate, reducing eavesdroppers’ achievable rate to near zero, while simultaneously maintaining legitimate user’s rate. The approach not only strengthens security but also preserves system effectiveness, demonstrating robust convergence properties. This makes it a practical and promising solution for secure UAV communication.