Fault-tolerant 3-D topology construction of UAV-BSs for full coverage of users with different QoS demands

Deploying Unmanned aerial vehicle mounted base stations (UAV-BSs) in post-disaster areas or battlefields, where the ground infrastructures are missing or destroyed, can quickly restore communication coverage. Due to the unstable and hostile properties of the environments, the ability to maintain the connectivity of the UAV-BSs network should be considered. In this paper, we study the deployment of UAV-BSs to provide full coverage for users with different quality of service (QoS) demands. The objective is to minimize the number of UAV-BSs under the constraints of user demands and UAV-BS service abilities. Besides, in absence of ground base stations, we also aim to construct a bi-connected topology for the UAV-BS network. However, the formulated problem, as a special instance of the geometric disk cover (GDC) problem, is NP-hard. To tackle this problem, we propose a heuristic algorithm, named Improved QoS-Prior Coverage and bi-Connectivity (IQP2C), by separately solving the user coverage and bi-connected topology construction subproblems. Firstly, IQP2C provides full coverage for users with minimum covering UAVs. Then, we propose an altitude-cluster-based method extending from the 2-D Hamilton cycle to construct bi-connectivity for the UAV-BS network. Simulation results validate the effectiveness of IQP2C in meeting different QoS demands and constructing fault-tolerant topology. Moreover, IQP2C outperforms other baselines in terms of minimized number of UAV-BSs for user coverage, minimized number of UAV-BSs for bi-connectivity as well as running time.