Event-Triggered Stigmergic Coordination for Communication-Efficient Heterogeneous UAV–UGV Search and Verification

Communication constraints can limit the scalability and resilience of heterogeneous robot teams operating in search-and-verification missions. This paper presents an event-triggered stigmergic coordination framework in which unmanned aerial vehicles (UAVs) patrol assigned sectors and deposit information into a shared digital-pheromone field only when relevant events occur. An unmanned ground vehicle (UGV) receives no target coordinates or direct task commands; instead, it selects and approaches targets using only the shared pheromone map. The framework was implemented using ROS 2, PX4 and Gazebo with three UAVs and one Husky UGV. The primary comparison evaluated event-triggered communication against continuous communication, while a periodic sensing-and-deposition policy was retained as a secondary benchmark. The study used 36 paired experimental blocks and 108 total runs. Relative to continuous communication, the event-triggered method reduced serialized pheromone payload bytes by 94.44% while satisfying prespecified noninferiority criteria for search-completion and mission-verification times. All 36 event-triggered missions completed successfully, with an exact one-sided 97.5% lower completion-probability bound of 90.26%, exceeding the prespecified 90% floor. Against the secondary periodic benchmark, the observed payload reduction was 47.30%, but its upper confidence bound did not satisfy the prespecified 50% superiority criterion. Because the frozen periodic implementation checked for target observations only when its transmission interval elapsed, that comparison combines sensing-opportunity and communication-policy differences. These results support event-triggered digital pheromones as a communication-efficient coordination mechanism relative to continuous communication under the evaluated idealized nominal simulation conditions.