Establishing UAV-Aided VBSs for Secure Multicasting

In this letter, we consider a UAV-aided multicasting system where the UAV is entasked with the job of disseminating a common file to multiple legitimate users (LUs) in the presence of multiple eavesdroppers. Due to the existence of line-of-signt (LoS) links between the UAV and the ground eavesdroppers, the delivery strategy of the UAV requires to be carefully designed so as to prevent the eavesdropping attack. To encourage advantageous secure transmission channels, we propose to serve the LUs in groups by letting the UAV sequentially visit favorable delivery points, i.e., the locations of vitrual base stations (VBSs). Accordingly, the placement optimization of VBSs is formulated as an advanced N-center (ANC) problem, which is NP-hard. To solve it, we put forward a branch-and-bound algorithm that iteratively invokes the advanced minimum enclosing ball (AMEB) procedure. Followed by the traveling salesman problem (TSP) algorithm, the flying trajectory of the UAV can be derived. Last, the numerical results demonstrate that our proposed algorithm can greatly cut down the mission completion time while guaranteeing security compared to the benchmark.