Robot Swarm Design Patterns

Information Exchange near Worksites

Category:

Information Aggregation pattern

Problem:

The information exchange of robots needs to be regulated.

Applicability:

Uninformed robots are likely to encounter data transmitters, i.e., other robots or non-robot data storage devices, near worksites, for example, when robots remain near worksites for a sufficient amount of time, when worksite and/or robot density are high or when robots have a large communication range (Pitonakova et al., 2018).

Solution:

Robots only exchange information while they are near worksites. Note that in the BDRML syntax, the conditions of the two relations, that connect the "Work" behaviour with the "Worksite data int." and "Worksite data ext." data structures, have an "and" operator. This ensures that the conditions always have to be met when this design pattern is combined with other patterns, allowing this pattern to regulate positive feedback loops of others.

BDRML representation of the Information Exchange near Worksites design pattern.

Feedback Loops:

Positive feedback loops already present in the swarm behaviour are regulated by only allowing information exchange near worksites.

Parameters:

• Proximity threshold: Maximum distance at which a robot is considered to be "near a worksite".

Forces:

• The proximity threshold value represents a trade-off between how much displacement and misinformation cost the robots will incur and how much recruitment can take place. If the threshold is large, robots can recruit while being further away from worksites, and thus cover a larger recruitment area, but new recruits incur larger costs.

Consequences:

• After an initial worksite discovery by a robot, the range at which other robots can find the worksite is enlarged, increasing the swarm’s scouting success (Sugawara and Watanabe, 2002; Sarker and Dahl, 2011; Pitonakova et al., 2018)
• The information gain rate depends on the structure of the environment, especially on worksite density, and on the range at which data transmitters can be detected and communicated with (Pitonakova et al., 2018)

Known Uses:

Has been used to extend the range at which robots sense worksites during foraging (Sugawara and Watanabe, 2002; Pitonakova et al., 2018), package delivery (Wawerla and Vaughan, 2010) and general event-servicing (Ducatelle et al., 2014).

Related Patterns:

An alternative to the Information Exchange Anywhere pattern, providing information flow regulation by localising information sharing to areas around worksites. Usually combined with the Broadcaster pattern to achieve foraging behaviour similar to that of as sheep (Michelena et al., 2010) and fish (Lachlan et al., 1998), where a foraging robot attracts more foragers that are nearby (Sugawara and Watanabe, 2002; Wawerla and Vaughan, 2010; Ducatelle et al., 2014; Pitonakova et al., 2018).