New Wireless Standards Challenge 802.11b

by Glenn Fleishman

For a while, we had unity.

Since 1999, wireless networking has simply been IEEE 802.11b -- dubbed "Wi-Fi" (for wireless fidelity) last year by an industry certification group, in an attempt to make it more user friendly.

For two years, 802.11b reigned supreme, gathering momentum last year as prices plummeted. Wi-Fi operates at 11 Mbps at distances from 50 to 150 feet indoors to well over 1,000 feet line-of-sight outdoors. It works on Windows, Macintosh, and various Linux/Unix/BSD flavors, sending TCP/IP and other packet data as an extension to plain old Ethernet networking.

But 2001 brings four new flavors to the wireless pot, mixing in disparate elements that might spoil the soup. Some of these standards have been kicking around for a year or more and are about to be commercially deployed; others are new, and may supplant 802.11b entirely. These specs include 802.11a and 802.11g from the IEEE, and the commercially supported HomeRF and Bluetooth protocols.

HomeRF, Bluetooth, and 802.11g all share the 2.4-GHz band with 802.11b. They have to co-exist or they threaten to overwhelm one another. The FCC tests and approves devices intended for use in this unlicensed band to ensure that they conform to tight interference requirements; your use of equipment can't impact other users, which may include wireless networking and a variety of industrial, scientific, and medical (ISM) devices. The FCC doesn't ensure, however, that multiple devices you deploy in your own space are non-interfering; that's up to trade groups.

802.11g: Barreling Down the Wireless Highway

The "g" flavor is the IEEE wireless LAN working group's attempt to boost speeds in this band from 11 Mbps to 22 Mbps without altering other perfectly workable aspects of 802.11b

The IEEE's 802.11 Task Group G had been considering two competing modulations that would allow the faster speed. All these wireless devices use spread-spectrum broadcast technology, which distributes information across many frequencies in an alternating pattern, so you never continuously occupy any one part of the band. Currently, the FCC (and, by extension, most of the regulatory bodies from other countries) allows only two kinds of spread-spectrum use: frequency hopping (FH), employed by HomeRF and Bluetooth; and direct sequence (DS), used by 802.11b.

Spread-Spectrum Technologies

Frequency hopping switches between preset ranges of frequencies, from several times per second to several thousand times per second, depending on the standard. Bluetooth, for instance, hops among 75 one-Mhz-wide segments in the 2.4-GHz band.

Direct sequence signals are sent in parallel across an entire range of frequencies, using techniques that attempt to prevent the continuous use of any given segment to prevent interference.


Related Article:

Introducing the Xircom 802.11 Module for the Visor

Comment on this articleWe've been having a great time with 802.11b at the O'Reilly Network, linking up laptops, Visors, and even a long-distance long shot. Tell us about your wireless network experiences.
Post your comments

Two types of direct sequencing are competing to become the 802.11g standard. Texas Instruments has been promoting a technology called packet binary convolutional code (PBCC), which it said offered better backward compatibility with earlier versions, ensuring that 802.11b devices would remain useful as organizations upgraded.

Intersil is pushing a modulation called wide-band orthogonal frequency division multiplexing (OFDM), which is used under the same and different acronyms for xDSL transmission and other tasks where a wide band of frequency can achieve higher efficiency through subdivision. Wi-LAN, which holds a Canadian patent on the technology has information on OFDM. Both of these technologies are actually old modulations reinvigorated by the arrival of faster, smaller, and cheaper chips that make them practical for wireless networking.

Recently, the 802.11 Task Group G eliminated Texas Instruments' contender, PBCC, from consideration for the 802.11g protocol. But TI says it will pursue the technology and sell it as a wireless networking chipset compatible with 802.11b up to 11 Mbps. PBCC was already approved for use by the IEEE with 802.11b at 11 Mbps, although it's not what manufacturers agreed to implement.

OFDM isn't the clear winner yet: At least 75 percent of the working group has to approve it, and if it fails, the group can go back to the drawing board for a new 802.11g technology. It has, however, already been approved for use with 802.11a, the 54-Mbps, 5-GHz standard discussed below.

Pages: 1, 2

Next Pagearrow