New mesh-networking technology will allow soldiers to more quickly search an area for signs of nuclear contamination. A company called Rajant has combined mesh radio transmitters with radiation-sensing backpacks to create a system that automatically sets up a communications mesh and displays a map of radiation across a region.

Mesh networking offers a fast, cheap way to construct a communications network. Instead of sending messages via a central command point, information hops from one node to another until it reaches its destination. A number of companies use static mesh networks for tasks such as traffic monitoring and environmental sensing, but creating reliable mobile mesh networks is more challenging. This is because each node must constantly track its moving neighbors to figure out how best to pass on a message while also preserving energy and bandwidth. Rajant addresses this problem by having nodes monitor just a few of their closest neighbors at any time.

For the detection system, Rajant's communication nodes, called BreadCrumbs, are connected to backpack sensors that detect radioactive material including plutonium and enriched uranium; the sensors are made by a company called Nucsafe. Team members wearing the sensors branch out and perform reconnaissance of an area. Data from each node hops back to a main computer, which builds a map showing the position of each node and its radiation data while individual users can see a map of their pack's results on a wrist-worn display or a laptop. Rajant presented the newest version of the system at the 2009 Soldier Technology Conference in Florida last month.

Each BreadCrumb can communicate with a peer that is up to five miles away, says Glenn Booth, vice president of marketing for Rajant. He adds that the mobile network has enough bandwidth to transmit a video stream or VoIP, even with hundreds of nodes all moving in different directions. The company already sells the wireless technology to mining companies and the military, and a single BreadCrumb device costs up to about $5,000.

"Building a reliable network is difficult because of mutual interference between radio nodes," says Dipankar Raychaudhuri, who works on mobile mesh networks for vehicles at Rutgers. Networks work with a certain density of radios, he says, but "can fall apart if radios move out of range in uncontrolled settings."

"The problem with completely mobile networks is that there is no guarantee of connectivity," adds Nader Moayeri, who works on mesh and ad hoc networks for the National Institute of Standards and Technology. "One other challenge is the capacity of the network," says Moayeri. Normally, as each node moves, it has to recalculate the best routes for a message. "That's considerable overhead," he says. "It eats up bandwidth you could be using for sending actual data."

Another way to improve a mobile network is to use several radio transmitters. For example, a company called MeshDynamics has developed transmitters that use two radios to send and receive data instead of just one.