Wait-Free Gathering of Mobile Robots

TL;DR

This paper presents a self-stabilizing algorithm for gathering multiple mobile robots in the semi-synchronous model, capable of handling any number of crash faults, advancing fault-tolerance in distributed robot coordination.

Contribution

It introduces the first solution for gathering correct robots despite multiple crash failures, assuming strong multiplicity detection and chirality.

Findings

Achieves gathering with any number of crash faults in semi-synchronous robots

Works from any initial configuration except bivalent configurations

Self-stabilizing and resilient to crash failures

Abstract

The problem of gathering multiple mobile robots to a single location, is one of the fundamental problems in distributed coordination between autonomous robots. The problem has been studied and solved even for robots that are anonymous, disoriented, memoryless and operate in the semi-synchronous (ATOM) model. However all known solutions require the robots to be faulty-free except for the results of [Agmon and Peleg 2006] who solve the gathering problem in presence of one crash fault. This leaves open the question of whether gathering of correct robots can be achieved in the presence of multiple crash failures. We resolve the question in this paper and show how to solve gathering, when any number of robots may crash at any time during the algorithm, assuming strong multiplicity detection and chirality. In contrast it is known that for the more stronger byzantine faults, it is impossible to gather even in a 3-robot system if one robot is faulty. Our algorithm solves the gathering of correct robots in the semi-synchronous model where an adversary may stop any robot before reaching its desired destination. Further the algorithm is self-stabilizing as it achieves gathering starting from any configuration (except the bivalent configuration where deterministic gathering is impossible).