Robots with lights

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 Fsync, Ssync and Async models when lights are present, we call this model 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.