Expendable robots that can be tossed into a building or over a wall, much like a hand grenade, are being developed for the U.S. military by iRobot, the maker of the popular Roomba robotic vacuum cleaner. But rather than exploding, these new bots will be used to set up communications networks to assist soldiers in urban battlefields.

The robots, called LANdroids, are being funded by the Defense Advanced Research Projects Agency (DARPA) as part of a $3 million three-year research program. The aim is to create expendable robots that will be able to overcome the communications problems that soldiers currently face in built-up areas.

"These robots will be used to allow the war fighter to rapidly deploy, maintain, and reconfigure a communications infrastructure, enabling war fighters to stay connected to their lines of communication in dynamic urban environments," says Chris Jones, research program manager of iRobot, which is based in Burlington, MA.

Existing radio communications networks used by the military work well when there is line of sight, but urban environments can hinder this. Obstacles and structures can reflect, refract, diffract, or absorb the radio signals, leading to signal loss and attenuation. The overall effect is that soldiers often have to work with poor and unreliable radio communications.

The LANdroids will be designed to overcome this problem using an autonomous positioning system that will help the robots adapt the communications networks as needed. To do so, the bots will use the 802.11g Wi-Fi standard to form mobile ad hoc networks that can repair and reroute themselves if, for example, the enemy destroys a robot.

But to meet DARPA's requirements, each LANdroid will have to weigh less than a kilogram and have an overall volume of less than one liter--that's about 10 centimeters long, says Jones. A single soldier should be able to carry more than one unit and be able to easily throw them into position, say, onto a roof. All this will cost no more than $100 per unit.

"It's certainly doable," says Chris Melhuish, director of the Bristol Robotic Laboratories at the University of the West of England, in the United Kingdom. But the biggest challenge will be power management--for example, ensuring that the robots get the best range while maximizing the bandwidth of the communications channels. "If it's too far away, then the bandwidth has to go down," Melhuish says.

Then there is the impact of mobility on the robot's power supply, he says. "Going up and down stairs, being able to peer out of windows--these are things that we take for granted but are difficult for a robot." Robots can do these things, but it comes at a power cost.

Fortunately, DARPA's vision doesn't require stair climbing. In fact, making the robots mobile is not so much to allow them to travel as to enable them to position themselves to get an optimal signal. In an urban environment, where an area can be flooded with multiple signals reflecting off structures, moving a relatively short distance of less than a meter can have a dramatic effect on signal quality.

Even so, the LANdroid will still be required to be smart enough to avoid obstacles and navigate a typical indoor environment, be it concrete or carpet. What's more, it will have to be able to do so at speeds of half a meter a second and be capable of functioning for up to 10 hours. Both requirements could prove difficult to implement in a small robot.

The form and means of locomotion have yet to be decided, says Jones. But, he says, the pace of the robots' development is likely to be rapid. First prototypes could be ready by the end of the year.