Realm: Real-Time Line-of-Sight Maintenance in Multi-Robot Navigation with Unknown Obstacles

Multi-robot navigation in complex environments relies on inter-robot communication and mutual observation for situational awareness. This paper studies the multi-robot navigation problem in unknown environments with line-ofsight (LoS) connectivity constraints. While previous works are limited to known environment models to derive the LoS constraints between robots, this paper eliminates such requirements by directly formulating the LoS constraints from realtime LiDAR scans, adopting techniques in point cloud visibility analysis. Based on that, we propose a novel LoS-distance metric to quantify both the urgency and sensitivity of losing LoS between robots considering their potential movements. Moreover, to address the imbalanced urgency of losing LoS between two robots, we design a fusion function to capture the overall urgency while generating gradients that facilitate robots' collaborative behavior to maintain LoS. The team connectivity is guaranteed by encoding the LoS constraints into a potential function that preserves the positivity of the Fiedler eigenvalue of robots' underlying graph. Finally, we establish a LoS-constrained exploration framework integrating the proposed connectivity controller. We showcase its applications in multi-robot exploration in complex unknown environments, where robots can always maintain the LoS connectivity through distributed sensing and communication while collaboratively exploring unknown environments. Our implementations are available at https://github.com/bairuofei/LoS_constrained_navigation.