A team of mobile robots carrying radiation detectors in a remote building or at a waste burial site has a mission: Autonomously build a map of radiation levels in the area suspected of contamination. Through wireless communication the robots coordinate their activities to ensure a complete radiation profile of the building or waste site.
In such areas, the infrastructure for conventional wireless networks is lacking, and the wireless connectivity can be quite unpredictable. For example, in a typical building, a robot mapping one room for radiation cannot communicate directly by radio with a robot in another room because radio waves cannot pass through the thick walls separating the rooms. A possible solution to this problem has been devised at ORNL. To foster robust communication between robots and more generally mobile nodes, ORNL's Nageswara Rao has developed the "connectivity-through-time" protocol and implemented a system using NetLet software in which a robot serves as a "router."
In a recent demonstration at ORNL, a "mail" robot mapped the hall connecting two rooms, each of which was being mapped by robots not in direct wireless contact. As the robot in the hall moved past the entrance to each room, it communicated, by radio, with the robot mapping the room, keeping track of its progress in generating the radiation profile and the location and amount of building space that remained to be mapped.
The mail robot picked up a message from a robot in one room and delivered the message to a robot in the other room, thus allowing these robots to communicate with each other. Though never before possible, with this new system for improving quality of service in wireless communication, robots can exchange messages under conditions of highly unpredictable, wireless connectivity.