Abstract
The classic Look-Compute-Move model of oblivious robots has many strengths: algorithms designed for this model are inherently resistant to a large set of failures that can affect the memory of the robots and their communication capabilities.
However, modern technologies allow for cheap and reliable means of communication and memorization. This is especially true if relatively low performances are needed, such as very limited communication bandwidth or constant memory. A theoretical model that expands the classic Look-Compute-Move by adding a minimal ability to communicate and remember is the model of robots with lights. In this model each robot carries a luminous source that it can modify at every cycle. The robot decides the color of its light during its Compute phase, and the light assumes such a color at the beginning of the next Move phase. Other robots can see the color of this light during their Look phases. The light will remain unaltered until the robot that carries it decides to change its color.
Typically, the number of available colors is very limited, i.e., it is constant with respect to the number of robots in the system.
In this chapter we will discuss the hierarchy of \(\mathcal{F}{\textsc {sync}}\), \(\mathcal{S}{\textsc {sync}}\), and \(\mathcal{A}{\textsc {sync}}\) models when lights are present, we call this model \(\mathcal{LUMINOUS}\). Moreover, we will see how lights are applied to solve classic problems such as rendezvous and forming a sequence of patterns. Finally, we will see how lights have been exploited in models where the visibility of robots is limited by the presence of obstructions.
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- 1.
Note that setting the light at the end of the compute phase is equivalent to set the light at the beginning of the move phase.
- 2.
We say \(\mathcal{F}{\textsc {sync}}\) model as shorthand for the model of \(\mathcal{OBLOT}\) (or \(\mathcal{LUMINOUS}\)) robots with \(\mathcal{F}{\textsc {sync}}\) scheduler.
- 3.
In a rigid model robots always reach the destination when performing the move. In a non-rigid model robots may be stopped before reaching the destination, however they travel of at least a fixed unknown \(\delta >0\).
- 4.
The neighbors are the adjacent robots on the convex hull boundary.
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Di Luna, G.A., Viglietta, G. (2019). Robots with Lights. In: Flocchini, P., Prencipe, G., Santoro, N. (eds) Distributed Computing by Mobile Entities. Lecture Notes in Computer Science(), vol 11340. Springer, Cham. https://doi.org/10.1007/978-3-030-11072-7_11
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