Decentralized Topological Mapping for Multi-robot Autonomous Exploration under Low-Bandwidth Communication

This paper concerns a mapping framework for multi-robot exploration of underground environments with only very limited communication available. We focus on multi-robot map building and coordination to explore large areas with real-time planning to long distances. The considered communication can broadcast only 100 B/s, and therefore, we propose coordination planning using two terrain models. The first model is a dense 3D map built by each robot individually to identify explorable places and generate detailed plans to avoid un-traversable areas. The second model is a global topological map built in a decentralized manner by exchanging tiny 12 B packets between the robots. The feasibility of the proposed approach has been verified in the real-world autonomous exploration mission and various multi-robot scenarios inspired by a virtual cave circuit of the DARPA Subterranean Challenge while adapting two different decentralized coordination strategies.

I. Introduction

Robotic exploration is a way to avoid risk to humans in dangerous environments in search missions of unknown areas such as underground space mapping or disaster response scenarios. In particular, we are motivated by the DARPA Subterranean Challenge [1] (SubT), where a team of robots is requested to search subterranean environments of mines, caves, and urban-like underground infrastructure. The mission is to search unknown environments for known artifacts such as survivor, cell phone, or backpack and report their position to the operator with the precision of 5 m. Therefore, the problem combines an exploration of the environment to identify areas where the artifacts can be located and an efficient search strategy to cover possible locations by sensors to recognize the artifacts. This paper focuses on mapping, navigation, and robot coordination using ground robots under very limited communication.