Brief Announcement: Wait-Free Gathering of Mobile Robots

Abstract

Robot Systems. This paper considers distributed systems of autonomous robots that can move freely on the two-dimensional Euclidean space, have visibility sensors (to see other robots, obstacles etc.) and can perform computations. One of the fundamental problems in distributed coordination of robots is to gather the robots at a single location. The gathering problem has been studied under various models with the objective of determining the minimal set of assumptions that still allows the robots to gather successfully within a finite time. For example, it is known that gathering can be solved even if the robots are anonymous (indistinguishable from each-other), oblivious (no persistent memory of the past), and cannot communicate explicitly with each other (except for indirect signaling using movement). Further, the robots may not share a common sense of direction. Robots operate in cycles that comprise look, compute, and move phases. The look phase consists in taking a snapshot of the other robots positions. In the compute phase, a robot computes a target destination, based on the previous observation, using a deterministic algorithm and in the move phase, the robot moves toward the computed destination (although the move may end before reaching the target destination). We consider the semi-synchronous ATOM model [4], where each cycle is considered to be atomic but only a subset of the robots may be active in each cycle. The robots are modeled as points on the Euclidean plane and the objective is to gather all robots at a single point.