Robust AN-Aided Secure Beamforming Design for A2G Communication Networks with UAV Jitter

Vibrations of UAV platform have great negative impact on establishing robust and secure transmission link in air-to-ground (A2G) wiretap system. In this paper, we investigate robust and secure beamforming in a downlink A2G wiretap network considering the impact of UAV jitter. Worst-case secrecy rate maximization by jointly optimizing the beamformer of confidential signal and artificial noise signal is studied. Detailed, considering the impact of UAV jitter on the antenna array response, the worst case indicates the scenario with the minimum legitimate data rate and the maximum eavesdropping data rate. The formulated problem is a non-convex optimization. To tackle it, auxiliary variables are introduced and Taylor expansion is employed to linearize the term related to each auxiliary variable. Further, the non-convex problem is then reformulated with linear approximation for channel variations and linear matrix inequality alternation for constraints with the aid of S-procedure and Cauchy-Schwarz inequality. Finally, a robust iterative algorithm is proposed to obtain the optimal solutions to the reformulated problem. Numerical results demonstrate the effectiveness of the proposed robust beamforming scheme and the solutions.