More tinkering on the way for wireless ISP spectrum

By , IDG News Service |  Mobile & Wireless

"My WISP is located in [radio frequency] hell," Michael Anderson, co-owner of PDQLink Wireless, in North Aurora, Illinois, wrote in an e-mail interview. "I drove home from one of my towers a few weeks ago. ... the distance was less than eight miles. My laptop picked up over 404 access points." The radio waves produced by those home access points can go beyond the walls of the house and interfere with a WISP's longer range transmission, he said. Anderson also is chairman of Part-15.org, an group of WISPs.

Last Mile Wireless LLC serves more than 300 local residences and businesses in Preston, Idaho, where DSL and cable aren't available and dialup speeds are slow, according to TJ Burbank, a partner in the company. The operator's 2.4GHz long-range, directional Wi-Fi service runs into interference from another WISP's 2.4GHz network, and Burbank is looking forward to getting access to more unlicensed spectrum and being able to use WiMax.

"Unless we add additional broadcast locations on the other side of the valley ... we really can't add much more 2.4GHz stuff now," Burbank said. "We would love to own a piece of spectrum, but if it's going to be US$50,000 a year or something, we'd be more willing to deal with the interference," he added.

In response to requests from WISPs, the FCC proposed allowing new uses of the 3650MHz-to-3700MHz band, with restrictions to prevent interference with the satellite Earth stations. The rules for the band call for "non-exclusive" licensing, under which service providers would not have to buy a license but would have to register their base stations with the FCC and show that they were not interfering with an existing user. Among the rules is a requirement for "contention-based" methods for preventing interference among multiple users. The FCC left it to industry to determine how it would meet the contention requirement.

Contention in wireless networks generally means the way two transmitters negotiate when they are using the same channel at the same time, said Mitch Vine, director of strategic marketing at wireless broadband equipment vendor Redline Communications Inc. Basically, a transmitting station "listens" for someone already transmitting in that channel, and if it detects someone, it holds off. If this is what the FCC is demanding in the 3650 band, WiMax would not comply, Vine said. In its current form, WiMax instead puts senders in different time slots where they have a given frequency to themselves, he said.

Vendors and service providers said it's not clear what the FCC means by a contention-based system. They don't all agree on how hard it will be to resolve the issue.

"The industry could come up with something, but it's going to take time. It's not a trivial thing to do," Vine said.

At least two vendors have something to say about the contention requirement.

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