Energy Minimization for Robust Secure Transmission in UAV Networks With Multiple Colluding Eavesdroppers

This letter investigates an unmanned aerial vehicle (UAV) aided wireless network where a UAV transmits confidential data to multiple legitimate receivers (LRs) in the presence of multiple colluding eavesdroppers (Eves) with imperfect location information. We formulate a mixed-integer non-convex optimization problem to minimize the UAV energy consumption by jointly designing the robust trajectory and user scheduling, while ensuring that the required amount of data can be safely transmitted to LRs. Instead of resorting to
S
-Procedure commonly used in existing studies, we equivalently convert the problem to a more tractable form with the difficulty arising from the uncertainties in Eves' locations effectively resolved. After that, a penalty-based iterative algorithm is proposed to obtain a suboptimal solution with the aid of the block coordinate descent and successive convex approximation techniques. The remarkable energy-saving effect of the proposed scheme is demonstrated by numerical results.