Gathering of asynchronous robots with limited visibility

In this paper we study the problem of gathering a collection of identical oblivious mobile robots in the same location of the plane. Previous investigations have focused mostly on the unlimited visibility setting, where each robot can always see all the others regardless of their distance. In the more difficult and realistic setting where the robots have limited visibility, the existing algorithmic results are only for convergence (towards a common point, without ever reaching it) and only for semi-synchronous environments, where robots' movements are assumed to be performed instantaneously. In contrast, we study this problem in a totally asynchronous setting, where robots' actions, computations, and movements require a finite but otherwise unpredictable amount of time. We present a protocol that allows anonymous oblivious robots with limited visibility to gather in the same location infinite time, provided they have orientation (i.e., agreement on a coordinate system). Our result indicates that, with respect to gathering, orientation is at least as powerful as instantaneous movements. (c) 2005 Elsevier B.V. All rights reserved.