The trials and tribulations of 5 GHz, Part 2

Varying rules for using 5 GHz spectrum across different countries mean that vendors must ship 802.11a-compliant Wi-Fi products to different places with different capabilities turned on and off. But the industry now seems more willing to do it than it once was – if perhaps for no other reason than to set the stage for 802.11n.

Worldwide compliance has been one thorn in the side of 802.11a Wi-Fi technology, which is finding a home in mesh backhaul networks and, as more dual-band and tri-mode access points and clients ship, might see more action in the coming two years.

In addition to the global progress of regulatory matters, vendors have also improved their products. Traditionally, 802.11a products have consumed much more power than its 802.11b/g counterparts, for example, but vendors “all continue to push power levels on chipsets down,” says Chris McGugan, senior director of the wireless infrastructure division at Wi-Fi company Symbol Technologies. McGugan says Symbol will bring a flash 802.11a/b/g offering to market this year for users requiring more 802.11a options.

Meantime, current-generation 802.11a technology supports coverage ranges much closer to those of 802.11b than they once were. Even so, remaining range inequalities bring up design issues, particularly in using the generous number of channels available in 802.11a (and the forthcoming option to 802.11n) for real-time multimedia traffic.

For example, Intel cites the following indoor ranges for the Intel PRO/Wireless 3945abg Network Connection, announced at the Consumer Electronics Show this month, as typical:

* 802.11a: 40 feet @ 54Mbps / 300 feet @ 6Mbps

* 802.11b: 100 feet @ 11Mbps / 300 feet @ 1Mbps

* 802.11g: 100 feet @ 54Mbps / 300 feet @ 1Mbps

From one perspective, at the full theoretical maximum speeds, the bit per second per foot of 802.11a beats that of 802.11b: while the 11a network is only radiating 40% as far, it is transmitting 500% as fast. And network designers get four to seven times as many channels to use to design around interference as a big bonus.

On the other hand, with the range of 802.11a not even half that of 802.11b (or, more importantly, 802.11g, which has equal capacity) an 802.11a network would likely require more access points and more handoffs between access points. Until the fast-roaming specification (802.11r) and technology becomes solid, this could result in more overall coverage holes, which would be a negative for voice and other real-time sessions.

The proposed high-speed 802.11n draft standard currently under review by the IEEE specifies use of the 5 GHz band as an option, though it will be difficult to get around using it and still find 40 MHz channel bandwidth to use, as required to achieve 802.11n’s 100Mbps-plus speeds.