Search-and-Fetch with 2 Robots on a Disk: Wireless and Face-to-Face Communication Models

TL;DR

This paper studies a treasure-evacuation problem with two robots on a disk, comparing wireless and face-to-face communication models, and provides algorithms and bounds for minimizing evacuation time.

Contribution

It introduces a new distributed search problem, develops efficient algorithms for both communication models, and establishes lower bounds in the face-to-face setting.

Findings

Wireless communication allows continuous information sharing, leading to efficient evacuation algorithms.

Face-to-face communication can be optimized to exchange information without meeting, improving evacuation times.

A lower bound is established for the face-to-face communication model, indicating limits of efficiency.

Abstract

We initiate the study of a new problem on searching and fetching in a distributed environment concerning treasure-evacuation from a unit disk. A treasure and an exit are located at unknown positions on the perimeter of a disk and at known arc distance. A team of two robots start from the center of the disk, and their goal is to fetch the treasure to the exit. At any time the robots can move anywhere they choose on the disk, independently of each other, with the same speed. A robot detects an interesting point (treasure or exit) only if it passes over the exact location of that point. We are interested in designing distributed algorithms that minimize the worst-case treasure-evacuation time, i.e. the time it takes for the treasure to be discovered and brought (fetched) to the exit by any of the robots. The communication protocol between the robots is either wireless, where information is shared at any time, or face-to-face (i.e. non-wireless), where information can be shared only if the robots meet. For both models we obtain upper bounds for fetching the treasure to the exit. Our main technical contribution pertains to the face-to-face model. More specifically, we demonstrate how robots can exchange information without meeting, effectively achieving a highly efficient treasure-evacuation protocol which is minimally affected by the lack of distant communication. Finally, we complement our positive results above by providing a lower bound in the face-to-face model.