A Characterization of Semi-Synchrony for Asynchronous Robots with Limited Visibility, and its Application to Luminous Synchronizer Design

TL;DR

This paper characterizes semi-synchrony in asynchronous robots with limited visibility, providing conditions for synchronization, and introduces a luminous synchronizer that enables asynchronous robots to simulate semi-synchronous algorithms.

Contribution

It offers a necessary and sufficient condition for ASYNC execution to emulate SSYNC behavior and presents a luminous synchronizer algorithm for limited visibility robots.

Findings

Established a sufficient condition for ASYNC to SSYNC execution correspondence.

Proved the condition is necessary with probability 1 under a randomized adversary.

Designed a luminous synchronizer enabling ASYNC robots to simulate SSYNC algorithms.

Abstract

A mobile robot system consists of anonymous mobile robots, each of which autonomously performs sensing, computation, and movement according to a common algorithm, so that the robots collectively achieve a given task. There are two main models of time and activation of the robots. In the semi-synchronous model (SSYNC), the robots share a common notion of time; at each time unit, a subset of the robots is activated, and each performs all three actions (sensing, computation, and movement) in that time unit. In the asynchronous model (ASYNC), there is no common notion of time, the robots are activated at arbitrary times, and the duration of each action is arbitrary but finite. In this paper, we investigate the problem of synchronizing ASNYC robots with limited sensing range, i.e., limited visibility. We first present a sufficient condition for an ASYNC execution of a common algorithm ${\cal A}$ to have a corresponding SSYNC execution of ${\cal A}$; our condition imposes timing constraints on the activation schedule of the robots and visibility constraints during movement. Then, we prove that this condition is necessary (with probability $1$) under a randomized ASYNC adversary. Finally, we present a synchronization algorithm for luminous ASYNC robots with limited visibility, each equipped with a light that can take a constant number of colors. Our algorithm enables luminous ASYNC robots to simulate any algorithm ${\cal A}$, designed for the (non-luminous) SSYNC robots and satisfying visibility constraints.