Heterogeneous Multi-AAV Cooperation With Data Gathering, Offloading, and Wireless Charging in Wireless Sensor Networks

Unmanned Aerial Vehicles (UAVs) are increasingly deployed for time-sensitive data gathering applications in infrastructure-less network environments, such as large-scale wireless sensor networks (WSNs) and disaster communication areas. However, limited onboard energy and buffer capacities present critical challenges to UAV-assisted task execution, mission continuity, and service coverage. This paper proposes a two-tier UAV deployment (2T-UAV) mechanism with a cooperative design that assigns two distinct roles: mission-oriented UAVs, which are responsible for collecting prioritized data, and ferry-oriented UAVs, which provide in-air energy charging and buffer offloading services. The 2T-UAV mechanism determines the hovering routes of mission-oriented UAVs using a Weighted Traveling Salesman Problem (W-TSP) method that incorporates an importance factor reflecting data urgency. In addition, the mechanism develops a Nonlinear Least Squares-based Route (NLLSR) method to optimize the recharging routes of ferry-oriented UAVs. Through this cooperative design, the 2T-UAV mechanism minimizes total mission time while adhering to UAV energy and buffer constraints. Extensive simulations are conducted under both synthetic and real-world map scenarios. The results demonstrate that the proposed 2T-UAV scheme significantly reduces mission time, energy consumption, and data drop rate when compared with several geometry-based, TSP-based, and reinforcement learning-based approaches. These findings confirm the feasibility and benefits of dual-role UAV cooperation for efficient data collection in UAV-assisted WSNs.