The trials and tribulations of 5 GHz, Part 1

Earlier this month, I mentioned that 802.11a deployments have been relatively sluggish, given that the technology’s 12 to 23 non-overlapping channels in the 5 GHz range (compared to three in the 2.4 GHz range used by 802.11b and 11g) provide additional flexibility for designing around interference. As real-time multimedia traffic, including voice, joins mainstream enterprise Wi-Fi LANs, interference avoidance will become a larger issue for network operators.

As you likely know, 802.11a and 802.11b both became standards in 1999, but 11Mbps 802.11b networks flourished first. There are both regulatory and technical reasons.

One is that use of RF spectrum is consistent throughout the world in the 2.4 GHz band for 802.11b (and, now, 802.11g); however, the 5 GHz rules for 802.11a have been less uniform.

“802.11a RF is legal in about 25% of my 45 countries,” an architect for a global company who reads “Wireless in the Enterprise” observed by e-mail earlier this month. “We have mobility concerns that trump technical performance,” so he chose to deploy 802.11b/g instead of 11a. Other readers have written to say they have found few 802.11a client choices available.

Both situations have been improving. On the regulatory side of things, the World Radiocommunications Conference harmonized some worldwide 5 GHz spectrum for 802.11a use in 2003. The FCC added spectrum in the “middle band” – 5.150 GHz to 5.350 GHz and 5.47 GHz to 5.725 GHz – in 2004, putting North America’s 802.11a 5GHz spectrum use on a par with other major regions of the world.

“Virtually every country has approved some section of the 5 GHz band for use by WLAN products,” says Bill McFarland, CTO at WLAN chipmaker Atheros, who adds that his company’s chips can “tune to the entire band.”

Still, product compliance regulations from country to country differ (power levels, antenna types allowed, whether hazardous materials can be used in product manufacturing). It helps having the frequency bands better in line, but the different rules make 802.11a devices more difficult for vendors to ship (and their customers to deploy) globally.

On the client-availability side, Intel is converting its Centrino mobile product line to dual-band 5 GHz/2.4 GHz products; it announced its Intel PRO/Wireless 3945ABG Network Connection for supporting all 802.11 client types at the Consumer Electronics Show earlier this month.

Meanwhile, for those seeking additional enterprise-class 802.11a client options, here are some links to Wi-Fi Alliance-certified 802.11a client products:

* Internal client cards that support 802.11a

* 802.11a-capable USB client adapters