Coordinated multi-robot real-time exploration with connectivity and bandwidth awareness

While there has been substantial progress for multi-robot exploration of an unknown area, little attention has been given to communication, especially bandwidth constraints in time-sensitive and bandwidth-consuming tasks such as search and surveillance. In such tasks, video/audio streams of a newly explored area should be sent back to the base station in a timely manner. To address this issue, we propose Connectivity and Bandwidth Aware eXploration (CBAX), which is an efficient iteration based real-time exploration. CBAX divides the problem into frontier node placement, relay node placement with routing path selection, and the match of each robot with its target position. Moreover, we model bandwidth-constrained relay node placement into a new variant of the Steiner Minimum Tree problem and present our solution. While reducing the exploration time, CBAX maintains the network's connectivity and ensures the aggregated data flows are under the link capacity in transmission. Simulation shows that CBAX outperforms two recent exploration schemes qualitatively by demonstrating major improvement in terms of non-overflow transmission time and fully-connected transmission time. With enhanced communication quality, CBAX still reduces the exploration time, on average, by 40% and 15% respectively. In moderately dense scenarios, CBAX even decreases time by 50% and 25%.