Search-and-Fetch with 2 Robots on a Disk: Wireless and Face-to-Face Communication Models

We initiate the study of a problem on searching and fetching, motivated by real-life surveillance and search-and-rescue operations where unmanned vehicles, e.g. drones, search for victims in areas of a disaster. In treasure-evacuation, we are interested in designing algorithms that minimize the time it takes for a treasure (a victim) to be discovered and brought (fetched) to the exit (shelter) by any of two robots (rescuers) which are performing in a distributed environment (the case of searching and fetching with 1 robot has been previously considered).The communication protocol between the robots is either wireless, where information is shared at any time, or face-to-face, where information can be shared only if the robots meet. For both models we obtain upper bounds for fetching the treasure to the exit. Our algorithms make explicit use of the distance between the treasure and the exit, which is assumed to be known in advance, showing this way how partial information of the unknown input can be beneficial. Our main technical contribution pertains to the face-to-face model. More specifically, we demonstrate how robots can exchange information without meeting, effectively achieving a highly efficient treasure-evacuation protocol which is minimally affected by the lack of distant communication. Finally, we complement our positive results above by providing a lower bound in the face-to-face model.