Fault-Tolerant Dispersion of Mobile Robots

TL;DR

This paper presents new algorithms for dispersing mobile robots on graphs that are resilient to crash faults, improving efficiency and handling different initial configurations.

Contribution

It introduces fault-tolerant dispersion algorithms for both rooted and arbitrary initial configurations, with improved round complexity bounds.

Findings

Rooted configuration dispersion in O(k^2) rounds

Arbitrary configuration dispersion in O((f+l) * min(m, kΔ, k^2)) rounds

Enhanced fault-tolerance in robot dispersion algorithms

Abstract

We consider the mobile robot dispersion problem in the presence of faulty robots (crash-fault). Mobile robot dispersion consists of $k\leq n$ robots in an $n$-node anonymous graph. The goal is to ensure that regardless of the initial placement of the robots over the nodes, the final configuration consists of having at most one robot at each node. In a crash-fault setting, up to $f \leq k$ robots may fail by crashing arbitrarily and subsequently lose all the information stored at the robots, rendering them unable to communicate. In this paper, we solve the dispersion problem in a crash-fault setting by considering two different initial configurations: i) the rooted configuration, and ii) the arbitrary configuration. In the rooted case, all robots are placed together at a single node at the start. The arbitrary configuration is a general configuration (a.k.a. arbitrary configuration in the literature) where the robots are placed in some $l<k$ clusters arbitrarily across the graph. For the first case, we develop an algorithm solving dispersion in the presence of faulty robots in $O(k^2)$ rounds, which improves over the previous $O(f\cdot\text{min}(m,k\Delta))$-round result by \cite{PS021}. For the arbitrary configuration, we present an algorithm solving dispersion in $O((f+l)\cdot\text{min}(m, k \Delta, k^2))$ rounds, when the number of edges $m$ and the maximum degree $\Delta$ of the graph is known to the robots.