Swarm Relays: Distributed Self-Healing Ground-and-Air Connectivity Chains

The coordination of robot swarms - large decentralized teams of robots - generally relies on robust and efficient inter-robot communication. Maintaining communication between robots is particularly challenging in field deployments where robot motion, unstructured environments, limited computational resources, low bandwidth, and robot failures add to the complexity of the problem. In this paper we propose a novel lightweight algorithm that lets a heterogeneous group of robots navigate to a target in complex 3D environments while maintaining connectivity with a ground station by building a chain of robots. The fully decentralized algorithm is robust to robot failures, can heal broken communication links, and exploits heterogeneous swarms: when a target is unreachable by ground robots, the chain is extended with flying robots. We test the performance of our algorithm using up to 100 robots in a physics-based simulator with three mazes and several robot failure scenarios. We then validate the algorithm with physical platforms: 7 wheeled robots and 6 flying ones, in homogeneous and heterogeneous scenarios in the lab and on the field.