Airborne ground surveillance with multi-hop UAV networks

Cooperative utilization of unmanned aerial vehicles (UAVs) in public and military surveillance applications has attracted significant attention in recent years. Most UAVs are equipped with sensors that have limited coverage and wireless communication equipment with limited range. Such limitations pose challenging problems to monitor mobile targets. The thesis examines fulfilling surveillance objectives to achieve better coverage while building a reliable network between UAVs. Area coverage and cooperative multiple target tracking problems are investigated and linear integer programming models are presented for these problems. For the area coverage problem, the optimal placement of UAVs for a given area is investigated with varying coverage ranges and the results are discussed. Coverage of the map achieved by the UAVs and the maximum possible coverage area are compared under different coverage and communications constraints. For the cooperative multiple target tracking, the optimal placement of UAVs to monitor mobile targets where their mobility is modeled with the random waypoint mobility model is studied. The multiple target tracking problem is further extended by assuming a relay UAV within the fleet whose trajectory is planned in order to achieve a reliable connected network among all UAVs. Optimization problems are established for single-hop and multi-hop communications. Three algorithms are proposed for multi-hop communications and their performances are evaluated. The effect of the time horizon considered in the optimization problem is also studied. Performance evaluation results show that the trajectories planned for relay UAV by the proposed algorithms generates network topologies that remain connected for more than 90% of the maximum possible duration that the UAVs can be connected by an ideal relay.