Cooperative Exploration of Heterogeneous UAVs in Mountainous Environments by Constructing Steady Communication

Unmanned aerial vehicles (UAVs) must fly at low altitudes to execute certain missions when operating in complex mountainous areas. However, in these environments, UAVs lose their line-of-sight (LOS) communication with the ground station (GS) due to the obstruction of the mountains and are unable to retransmit information such as video, which will lead to mission failure or affect the flight safety of UAVs. To address this diffi- culty, this study proposes a cooperative planning method for heterogeneous UAVs by ensuring steady communication based on the shortest total mission time. To accomplish this goal, a re- lay UAV is positioned to enable indirect but constant LOS con- nectivity between the mission UAV and the GS. Specifically, to alleviate data storage pressure, a terrain lightweight modeling method is employed. In addition, a new LOS judgment model that constructs communication relay LOS links between com- munication nodes for complex mountain environments is pre- sented. This study considers different types of UAVs; for the fixed-wing UAV, the minimum turning radius constraints are taken into account to plan a flyable trajectory. The problem is formulated as the multi-step optimization model that accounts for communication constraints, obstacle and collision avoidance, and the performance constraints of heterogeneous UAVs to plan the trajectories of the mission UAV and relay UAV in order to maintain LOS links between the mission UAV and the ground station. Finally, the experimental results demonstrate that the proposed method is effective and ensures the completion of coop- erative exploration missions for heterogeneous UAVs in complex mountain environments.