DOD, wireless LAN industry debate 802.11a standard

The U.S. Department of Defense (DOD) and various industry groups are discussing ways to avoid interference between the next generation of wireless LAN (WLAN) devices and military radars that operate at frequencies above 5GHz, said various industry sources Tuesday.

One of the fastest growing segments of technology has been wireless Internet access devices based on the 802.11b standard, commonly known as Wi-Fi. This standard operates on the 2.4GHz frequency of the electromagnetic spectrum, and allows users to download data from the Internet at speeds up to 11M bps (bits per second).

However, another WLAN standard is coming into vogue. The 802.11a standard was also developed by the Institute for Electrical and Electronics Engineers, and operates at frequencies between 5GHz and 6GHz. It allows data to be exchanged at faster rates, up to 54M bps, but has a shorter operating range than the 802.11b standard.

Because the DOD operates a number of radar systems in the same frequencies as the 802.11a standard, the DOD is worried that increased adoption of 802.11a devices will cause interference between radar signals and the WLAN signals, said Badri Younes, director of spectrum management at the DOD at the Pentagon in Arlington, Virginia.

Concerns that the DOD was trying to reduce the spread of WLAN technologies in general was fueled by a report in the New York Times Tuesday that didn't distinguish between the fast-growing 802.11b technologies and the just-emerging 802.11a standard.

The DOD has no issues with the 802.11b standard, as it doesn't operate any radar equipment on that frequency, Younes said.

"But if the 5GHz frequency is compromised, there's no more spectrum" in which that radar equipment can operate, he said.

The debate boils down to the sensitivity of DFS (dynamic frequency selection) technology that currently exists in 802.11a devices to detect the presence of radar beams. When DFS detects a radar beam on a certain channel, it switches to another channel to avoid interfering with the radar beam. The DOD and the industry disagree on exactly how sensitive those devices should be, with the industry concerned about the ability of the device to operate correctly if they are constantly switching between channels.

"If the DFS technology is not sensitive enough, military radar may not be adequately protected from interference. On the other hand, if the DFS technology is too sensitive, the communications equipment won't work. The trick is to find the 'sweet spot' where radar is adequately protected and the communications equipment will work effectively," said Scott Harris, an attorney with Harris, Wiltshire & Grannis LLP in Washington, D.C. Harris represents Microsoft, Intel, and Cisco Systems on technology matters before the government.

One IT expert in the military who asked not to be named spoke of the modern-day logistics of warfare where military engagements are more likely to occur in heavily populated civilian locations and not on isolated battlefields. In such cases, there is more likelihood of civilian infrastructure interfering with the military infrastructure.

However, this is more of a battle over turf than over technology, said Barclay Jones, vice president for field operations for wireless infrastructure company Flarion Technologies Inc.

"This comes up all the time and they (DOD) throw their weight around at the cost to business and consumers," said Jones.

The DOD has been giving testimony for some time over conflicts between public and private access to wireless technology, and not just with the 802.11a standard.

In testimony last June, Steven Price, deputy assistant secretary for Spectrum, Space, Sensors and C3 Policy with the DOD testified over the use of another technology, called UltraWideband. The U.S. Federal Communications Commission earlier this year opened up that technology for public use.

Price testified that UWB "degraded the ability to use GPS (global positioning system) to navigate and land military aircraft and commercial airliners" and also degraded "the operation of government airport radars."

The DOD is working with the WLAN industry in hopes of reaching a compromise over the 802.11a technology before the June meeting of the World Administrative Radio Conference in Geneva, said both Harris and Younes. The WARC recommends spectrum allocation policies to regions around the world, which are not enforceable, but are generally followed by most countries, according to a source.

Two U.S. senators will propose a bill in the next session of Congress seeking to dedicate no less than 255MHz of spectrum below the 6GHz for the exclusive use of Wi-Fi devices. The bill will stipulate that the dedicated spectrum must not interfere with military uses.

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