Optimal Dispersion of Silent Robots in a Ring

TL;DR

This paper presents an optimal deterministic algorithm for dispersing silent robots with unique labels in an oriented ring network, achieving minimal rounds and memory, and addresses multiple source starting points.

Contribution

It introduces the first optimal dispersion algorithm for silent robots with multiple sources on a ring, with proven lower bounds matching the algorithm's complexity.

Findings

Algorithm disperses robots in O(log L + k) rounds

Proves a lower bound of Ω(log L + k) rounds for the problem

Uses O(log L) bits of memory per robot

Abstract

Given a set of co-located mobile robots in an unknown anonymous graph, the robots must relocate themselves in distinct graph nodes to solve the dispersion problem. In this paper, we consider the dispersion problem for silent robots \cite{gorain2024collaborative}, i.e., no direct, explicit communication between any two robots placed in the nodes of an oriented $n$ node ring network. The robots operate in synchronous rounds. The dispersion problem for silent mobile robots has been studied in arbitrary graphs where the robots start from a single source. In this paper, we focus on the dispersion problem for silent mobile robots where robots can start from multiple sources. The robots have unique labels from a range $[0,\;L]$ for some positive integer $L$. Any two co-located robots do not have the information about the label of the other robot. The robots have weak multiplicity detection capability, which means they can determine if it is alone on a node. The robots are assumed to be able to identify an increase or decrease in the number of robots present on a node in a particular round. However, the robots can not get the exact number of increase or decrease in the number of robots. We have proposed a deterministic distributed algorithm that solves the dispersion of $k$ robots in an oriented ring in $O(\log L+k)$ synchronous rounds with $O(\log L)$ bits of memory for each robot. A lower bound $\Omega(\log L+k)$ on time for the dispersion of $k$ robots on a ring network is presented to establish the optimality of the proposed algorithm.