Explicit Communication Among Stigmergic Robots

In this paper, we investigate avenues for the exchange of information (explicit communication) among deaf and mute mobile robots scattered in the plane. We introduce the use of movement-signals (analogously to flight signals and bees waggle) as a mean to transfer messages, enabling the use of distributed algorithms among robots. We propose one-to-one deterministic movement protocols that implement explicit communication among semi-synchronous robots. We first show how the movements of robots can provide implicit acknowledgment in semi-synchronous systems. We use this result to design one-to-one communication among a pair of robots. Then, we propose two one-to-one communication protocols for any system of n >= 2 robots. The former works for robots equipped with observable IDs that agree on a common direction (sense of direction). The latter enables one-to-one communication assuming robots devoid of any observable IDs or sense of direction. All protocols (for either two or any number of robots) assume that no robot remains inactive forever. However, they cannot avoid that the robots move either away or closer to each others, by the way requiring robots with an infinite visibility. In this paper, we also present how to overcome these two disadvantages (some activity of every robot and infinite visibility).Our protocols enable the use of distributing algorithms based on message exchanges among swarms of stigmergic robots. They also allow robots to be equipped with the means of communication to tolerate faults in their communication devices.