The goal of exploration is to cover an unknown environment in a minimum of time. The key problem with a team of robots is to allocate efficient target locations for each of them, so that they can parallel explore different regions.
An approach for exploration with unlimited communication abilities is used in : During the exploration a global map of the environment is built (known/unknown and obstacle free/unfree areas are mapped). The decision for which of the frontier locations (frontier to an unknown location) are allocated as the next targets is evaluated from two values: The cost of reaching this location (simple distance) and the utility. Whenever one robot chooses a location as a target, the utility of this and the adjacent locations are reduced to all other robots. Consequently an attractive location loses its attractiveness when it is targeted and other robots can explore other regions.
Results: This relative simple approach is needed to introduce quickness and robustness into the system. In real world experiments good results were achieved (see Figure: Coordinated exploration by three robots in a real world experiment; starting point is the left upper corner; Figure from ). This multi-robot system is more redundant, more fault-tolerant and faster in the exploration then a single robot.
Further works will deal with limited communication abilities, unknown relative positions of the robots, changing environments and dysfunctions of robots.
Reference:  W.Burgard, M.Moos, C.Stachniss, F.Schneider: "Coordinate Multi-Robot Exploration", International Conference on Robotics and Automation, IEEE, 2000, http://www.informatik.uni-freiburg.de/~stachnis/pdf/burgard05tro.pdf
NT061637N Ireneus Wior