Gathering problems for autonomous mobile robots with lights

An autonomous robot system is a distributed system comprising autonomous mobile robots that perform tasks of interest such as formation and flocking. In a basic model when robots have no lights (no memory and no communication devices), Gathering, a type of formation problem that asks all robots of the system to meet at a single point that is not known a priori, is impossible if the system is semi-synchronous (SSYNC, a subset of all robots is synchronously activated each time) or even centralized (only one robot is activated each time) [7], [23]. Furthermore, if robots have a multiplicity detection mechanism, Gathering is solvable only when the number of robots is odd. This work aims to further characterize the impact that different capabilities/assumptions (including light capability) have on the solvability of the problem. We introduce novel types of a view model called “set-view”, “arbitrary-view” and “multi-set-view,” and then propose six algorithms (five of these are optimal in terms of the number of colors of lights) to solve Gathering as a formation problem when robots have lights. The proposed algorithm in SSYNC shows that the light model is stronger than the multiplicity detection mechanism for solving Gathering as a formation problem.