DARPA TAKES FIRST STEPS TOWARD XG PROJECT

DARPA first formally outlined the XG program in Aug. 2001, characterizing it as a way to meet spectrum needs for 4th-generation wireless devices. The request for comments (RFC) it released Fri. marked the project’s “first milestone” by setting out the architecture a radio could use in executing those and system components, Marshall said. The “architectural framework” for XG includes how it fits into existing wireless technology such as 802.11a systems, he said. The RFC also sets out a policy specification “meta- language,” which could pave the way for an international standard that would allow radios to roam worldwide. The XG protocol that’s part of the RFC also lays out abstract behavior that system implementations would have to meet to ensure “enforcement” of the program’s policy. The program expects to finish its work in 3 years, he said.

The thrust of the program isn’t to lock into a particular technology or standard, such as an 802.11a or 802.11b Wi-Fi system, Marshall said. He said the Defense Dept. had a particular burden as part of its worldwide operations in having to obtain clearance from each nation where its radios operated. “We want to make the policy completely independent of the implementation so that policymakers can define essentially a space in which a radio could operate and how it interacts, independent of the technology,” he said: “If we do that right, we can build one set of policies for every radio and we don’t have to go around thinking what’s the policy impact of the next radio.” Under a “policy framework” that every type of radio could interpret, DoD would be able to negotiate one policy with each country, instead of having to work out agreements for each type of radio used, Marshall said. Examples of policy constraints could include maximum power, frequency and the time needed to vacate the spectrum under certain conditions, he said.

The XG program is looking for ways to increase spectrum efficiency by an order of magnitude for military radios and civilian applications. The program is designed to co-exist and complement sharing protocols of current Wi-Fi technologies. Marshall stressed the openness of the development process. “Anyone can imitate our protocols and behaviors without a license,” he said. The program also is looking at architectures for both standalone radios and ones that are “fully cooperative,” he said: “If a cellular provider wants to sublet spectrum, they can use our protocols to manage that process.”

As more “smart” devices such as software defined radios utilize spectrum, Kalle Kontson, a member of the FCC’s Technology Advisory Committee, said etiquette between how those systems interacted would play a greater role. He laid out a “bill of rights” for intelligence devices, including the right to use, on a noninterference basis, any frequencies as long as they were “mentally competent to accurately determine the possibility of interference that may result from their use of the spectrum.” Another condition on access would be that such devices constrain their use of the spectrum to the minimum amount of time and bandwidth they needed to do their job, Kontson said. All spectrum users also should have the right to operate without harmful interference from others, except when cases such as national emergency dictated otherwise. Systems also would have to be designed “to be reasonably resistant to interference,” he said.

“One of the more attractive places to apply such a generalized body of principles would be in the efforts by the FCC to open up more unlicensed spectrum,” Kontson said. “I would characterize it in terms of opening up unlicensed but highly regulated spectrum.” He said that would mean that along with permission to use such unlicensed spectrum, “we are having very high expectations on the kinds of behaviors, the kinds of intelligence and the kinds of device capabilities that come with that privilege. The XG program is providing some of those principles.”

Edmond Thomas, chief, FCC Office of Engineering & Technology, said the sector involving unlicensed wireless spectrum had been a “bright spot” in an otherwise downtrodden telecom sector. “One thing we are starting to think about is that if you want to try a different model, it might be appropriate to do it somewhere else in the band where indeed you don’t go in and break something that didn’t need fixing by ‘fixing’ it,” he said. “There is a dialog -- and it’s only dialog now -- possibly employing the bill of rights, you may want to think about doing that somewhere else in the band until you're confident that the model you are trying is also one that has legs.”

Thomas said that in general the policy reform ideas teed up in last fall’s Spectrum Policy Task Force report had been embraced as positive by most interest groups. “The interesting thing… is that no matter what constituency you talk about, they say the Spectrum Policy Task Force in the main is great, but try it in the other guy’s band,” he said. “One of the challenges that’s going to face the Commission is to try to move to implementing those recommendations in bands that are used, albeit periodically or continuously, making sure that they don’t create any real harm. And that’s where the finesse is.”