Secrecy Rate Degradation of Ground-to-Air Collaborative Beamforming Due to UAV Jitter

In this article, we consider the secure uplink transmissions from ground nodes to an unmanned aerial vehicle (UAV) receiver through analog collaborative beamforming (ACB). When the location information of the UAV receiver is available, ACB can be realized in a fully distributed manner, since each transmitting node can locally adjust its phase. ACB-based physical layer security (PLS) algorithm, where the virtual antenna array (VAA) elements are randomly selected at each transmit time unit, can effectively protect against eavesdropping attacks by creating artificial noise to the directions except the legitimate receiver (Bob). However, when Bob is mounted on the UAV, it can suffer from array gain loss due to jittering effects caused by airflow turbulence and mechanical vibration. Motivated by this issue, in this article, we investigate the impact of the UAV jitter on the secrecy performance. We derive the theoretical expressions of the secrecy rate both in the absence and presence of the jittering effects. Further, the simulation results show that the ACB-based PLS cannot guarantee non-zero secrecy rate even with the radial distance perturbations on the order of a few centimeters, especially when an eavesdropper (Eve) exists in close proximity to Bob.