DARPA looks to adaptive battlefield wireless nets

Advanced software research, commercial hardware are key enablers

A new Department of Defense project is trying to use cutting-edge wireless research to create a tactical radio net that can adapt to keep soldiers linked with each other on the battlefield.

Project WAND, for Wireless Adaptive Network Development, will exploit commercial radio components, rather than custom ones, and use a variety of software techniques and algorithms, many of them only just now emerging in mature form. These US$500 walkie-talkie-size radios will form large-scale, peer-to-peer ad hoc nets, which can shift frequencies, sidestep interference, and handle a range of events that today completely disrupt wireless communications.

WAND is part of a larger project by the Defense Advanced Research Projects Agency (DARPA) to create the Wireless Network after Next, a complete military communications infrastructure. WAND has two teams of contractors and researchers, with BBN Technologies heading the software development and Tyco Electronics heading up the software development.

"The average soldier on the ground doesn't have a radio," says Jason Redi, principle scientist for BBN's network technologies group, and the man overseeing the software work. Radios are reserved for platoon and company commanders, in part because of their cost: typically US$15,000 to US$20,000 each, with vehicle-mounted radios reaching US$80,000.

Families of soldiers have bought off-the-shelf walkie-talkies from companies like Motorola and mailed them to troops in Iraq. "It's a lousy way to communicate but it's better than what they have now."

WAND is an attempt to create low-cost radios with intelligent network software that does several things to make communications more pervasive, more efficient and more reliable in the battlefield.

One key technique is adaptive spectrum management. Radio spectrum today is divided into different bands, with each band assigned a particular use, for example, a slice for taxicabs, another for police, another for military use and so on. "But when you look at the actual use of the spectrum, much of it is not being used at any given moment," says Redi. "Adaptive frequency management lets the radio 'sniff out' the empty bands and use them."

Part of the WAND software will be doing this continual analysis of the spectrum covered by the radio. Another part will do opportunistic spectrum access, more commonly called dynamic spectrum access, to allow the radio to dive into that open spectrum and send and receive. As that band becomes congested or subject to interference, the software can shift the connection to another band, keeping the sessions intact.

Another part of the WAND software stack will draw from BBN's work in disruption tolerant networks (DTN). Conventional routing protocols assume an end-to-end network path that stabilizes quickly. Based on that path, the net computes routes and creates the router forwarding tables. But repeated disconnections and long delays, common in wireless nets, break this stable arrangement apart. New routing protocols and code are being designed to move data from node to node as connections become available, holding information in persistent storage in the meantime.

Finally, the software will have to manage all this for large numbers of client radios. The WAND target is up to 10,000 nodes within a relatively small area. "Managing that connectivity is a really difficult thing because links will be changing all the time," Redi says.

The software research in these various areas has been largely academic and still relatively recent, he says. The real challenge will be to bring all these together in a deployable, US$500 radio that actually works in the field.

The software advances are part of an growing R&D effort worldwide to create what are called "cognitive radios" (sometimes called software-defined radios, which are smart enough to understand spectrum, network and user activities, and then select the right radio waveforms, frequencies and protocols for optimal efficiency, performance and reliability.

Tyco is working to create US$500 radios that can span four independent channels from 900MHz to 6GHz, says Redi. The initial form factor delivered in September 2008 will be about the size of a large walkie-talkie, and shrinking with each new generation of radio technology. The goal is to avoid costly custom silicon and components, in order to exploit the economies of scale, and the rapid pace of innovation, in standardized, commercial wireless technology. The entire WAND project is part of a shifting mindset in military procurement to put more emphasis on rapid, cost-effective systems development, Redi says.

WAND is on a tight schedule. An initial technology demonstration is scheduled for January 2008, a second in September. "That's pretty outrageous even for some simple technologies," Redi admits.

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