16 vs. 22: Which Will Get the TV Spectrum?

By Ed Sutherland

April 01, 2005

There's never a lack of drama among the groups trying to settle on specifications for wireless. Witness the battle for the future among wireless broadband standards.

With the IEEE Atlanta Plenary Session over, news of progress on UWB and the high-speed 802.11n could overshadow a potential civil war between two factions scrambling to control what has been described as the nirvana of wireless spectrum.

It's almost fitting that a war of words between the somewhat beleaguered 802.16 (WiMax) proposal and the newly-developed IEEE 802.22 spec has taken on the proportions of a television drama. At stake is a swath of sub-900 MHz TV bandwidth the FCC proposes to open to unlicensed wireless use.

The FCC decision was greeted by WiMax-backer Intel as something akin to opening a lush new grazing land for wireless gadgets. Intel CTO Pat Gelsinger said the UHF/VHF spectrum represented "some of the most valuable spectrum available." For over half a century, vacant TV channels have been underutilized, Gelsinger said, and opening the spectrum "will help foster new technologies, create opportunities for business, and bring exciting new products to consumers." Not to mention the positive effect it might have on the embattled WiMax.

For months, proponents of 802.16 and 802.22 have traded barbs concerning who will take charge of the spectrum as it becomes available. In an effort to lower tension, Carl Stevenson, chair of the 802.22 Working Group (WG), made improving the atmosphere between the two camps a priority for the Atlanta session.

While working on the documents and merging the differing proposals will be key, Stevenson stressed that the tasks need to be accomplished "while doing our best to do so in a collegial fashion that avoids, or at least minimizes, the 'winner take all' competitive aspect that sometimes develops."

Developing that collegiate atmosphere may be difficult. Since the FCC's announcement in 2004, the IEEE groups have fiercely defended their individual turf. Why?

Allowing unlicensed wireless devices into the spectrum once dominated by licensed users—TV broadcasters—is a boon. The difference between the unlicensed 2.4 Ghz and 5 Ghz bands and the licensed 3 Ghz band, where TV channels reside, is akin to the difference between grazing in a rock-strewn pasture covered with well-worn grass stubble and grazing in an untouched field of emerald green.

At sub-900 MHz, wireless signals pass through buildings, trees and other obstacles. All such gear is non-line of sight (NLOS). Those signals travel up to three times farther than 2.4 Ghz, resulting in fewer base stations.

For WiMax, the advantages of sub-900 MHz access would translate to being more competitive with 3G, as well as gaining the fixed and mobile ubiquity it so dearly desires. Using the sub-900 MHz space could also solve the headache of 802.16e—WiMax's mobile variant of the future. At last count, there were more than 100 differing plans submitted.

But for unlicensed users to gain entry to the sub-900 MHz bonanza, the FCC requires that devices be able to detect and then avoid signals from incumbent broadcasters still using the spectrum. This is where 802.22 comes in.

In November, the IEEE announced the creation of 802.22 as a "standard to enable the deployment of wireless regional area networks (RAN) using the unused TV channels, while not interfering with the licensed services now operating in the TV bands." Specific to 802.22 is a cognitive wireless RAN Media Access Control Layer (MAC) and Physical Layer (PHY). The MAC and PHY layers "will provide for broadband systems that choose portions of the spectrum by sensing what frequencies are occupied," according to the IEEE.

The reaction was swift from members of the 802.16 camp, who don't see how it is any different from what they already do. The IEEE 802.16 WG then asked the IEEE to incorporate 802.22 into 802.16.

When announcing the proposed new standard, Stevenson said the specification "will complement IEEE 802.16 metropolitan networks, which do not include cognitive radio functions for sharing TV spectrum."

In December, Stevenson noted that the 802.16 group had altered its 802.16h plan for developing its own cognitive radio technology by expanding the scope to include "coexistence with primary users." The phrase is key in Stevenson's mind, because it changes 802.16's focus from avoiding interference between WiMax devices in unlicensed spectrum.

At the time, Stevenson wrote of his 802.22 WG that he was "concerned that there is an ambiguity in the scope that would potentially create a situation where 802.16 might assert that the scope of this project authorization request enables it to develop systems designed to operate on an unlicensed basis in the TV bands, which is clearly the scope of 802.22."

In response, the 802.16 group agreed that there may be some duplication. "It is possible that 802.16 and 802.22 may cover some overlapping frequency ranges -- clearly, 802.22 is also intended to coexist with primary users in the band, but it does not seem like we should prevent 802.16 from being a good citizen also," said Steve Shellhammer, head of the IEEE 802.19 Coexistence Technical Advisory Group.

As the IEEE tries to put down this internal revolt, vendor WiFi Wireless says it will launch its so-called '802.22-based' WiFi Key product late this year, well ahead of a final 802.22 specification. "We are estimating a publicly-available product to be announced and ready for ending 4th quarter 2005," says Matthew Walusko, WiFi Wireless' chief operating officer.

"I can categorically state that it's impossible to have 'an 802.22 gadget' since 802.22 has not yet been defined," says Stevenson. "We haven't finished our requirements document or taken a single proposal, and don't have a draft standard, let alone a final one. Until the IEEE 802.22 standard is fully defined, approved, and published, I don't see how anyone can claim compliance, or even 'based on,'" says Stevenson.

Stevenson says the initial requirements document for 802.22 will not be completed until May, and a first call for proposals is set for July.

Originally published on .

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