Trajectory and Power Design for Aerial CRNs with Colluding Eavesdroppers

Unmanned aerial vehicles (UAVs) offer wireless access services to terrestrial users without geographical limitations, making them integral to future communication systems. However, the openness of wireless channels and the mobility of UAVs pose significant security challenges to UAV-based communication systems. This work delves into the security of aerial cognitive radio networks (CRNs) with multiple location-uncertain colluding eavesdroppers. In this setup, a cognitive aerial base station transmits messages to cognitive terrestrial users using the spectrum resources of primary users. All secondary terrestrial users employ the maximal ratio combining scheme to decode the received message, as do all illegitimate receivers. To maximize the average secrecy rate of aerial CRNs, we jointly optimize the trajectory of the UAV and its transmission power while ensuring that the propulsion energy consumption remains within an acceptable threshold. To address the non-convex mixedvariable optimization problem, we propose an iterative algorithm based on Karush-Kuhn-Tucker condition and successive convex approximation. Numerical results validate the effectiveness of our proposed algorithm, demonstrating improved secrecy performance for airborne CRNs.