Time to say "bye-bye" to WiFi? Faster competition comes faster than expected

Computer Technology Review, Jan, 2002 by Joshua Piven

In a fractious wireless market, where multiple standards are constantly competing for spectrum space and consumer attention, is the sector now ready for 24Mbps products? Will it be ready for 54Mbps sometime late this year?

Ready or not, super-fast wireless is on the way, and computer professionals should be aware of the complexities and competing standards in this market, where 11Mbps (actually 7Mbps in the real world) is now considered too slow and a number of companies and products are currently vying for dominance in the fast lane.

Proprietary products incorporating parts of 802.11g--the new, faster WLAN specification--are expected early this year. But, confusingly, they have been beaten to the punch by products based on 802.11a (a standard approved with WiFi in 1999) which offers a maximum throughput of 54Mbps operating in the 5GHz range. But before you throw away those WiFi base stations, it's important to understand why both standards are being touted, and the technology observers expect will make them viable.

WiFi Wherefores

Most readers will be familiar with IEEE 802.11b, now commonly referred to as WiFi. In its current incarnation, WiFi operates at about 7Mbps in the 2.4GHz radio spectrum. Recent security concerns notwithstanding, WiFi is finding good acceptance among consumers and businesses alike, even as shorter-range technologies like Bluetooth continue to come to market. But the specification's speed limitations mean that it is unsuitable for bandwidth-hungry applications like high-quality video. Further, 2.4GHz devices found in the home use different protocols and compete for a relatively meager portion of the radio spectrum--about 84MHz--and tend not to cooperate, resulting in interference. Microwave ovens are one common culprit, but cordless phones can also wreak havoc, even to the point of disrupting WiFi LANs and DSL service. More recently, Bluetooth has been shown to interfere with WiFi networks, another issue to consider when making deployment choices.

At the end of last year, the IEEE 802.11 Task Group G approved its first draft of the 802.11g standard, which supports data rates up to 54Mbps in the 2.4GHz band. The group was meeting at press time and general industry speculation was that it would be approved by January. However, CTR obtained an email to Task Group G members from the group's leadership indicating that "the earliest we can expect to see an 'approved' 802.11g standard is late 2002 early 2003." (Requests for comment from Group G officials went unanswered.) The first interoperable products based on the specification will likely operate in the neighborhood of 24Mbps, with faster products in the second generation.

The current 802.11b spec, which was ratified in 1999, will serve as the basic reference design for future 2.4GHz devices that conform to .11g (see Fig). However, sometime later this year 2.4GHz WLAN products may be supplanted by those operating in the 5GHz spectrum, which has fewer technical problems than the lower frequency. Some products based on this technology are already on the market, and several new ones were announced at Comdex.

While 802.11b and .11g are in the same family of specification and both operate in the 2.4GHz band, operationally they are different. WiFi is based on direct-sequence spread-spectrum technology (DSSS), while the newer technology is primarily based on Orthogonal Frequency Division Multiplexing (OFDM). OFDM is a physical layer encoding scheme which divides a high-speed data stream into multiple, slower sub-streams that are transmitted over different frequencies in parallel and then re-assembled (multiplexed) by the receiver. Because of its orthogonal nature, OFDM is considered highly efficient: sub-channels can overlap, which means it uses less of the available radio spectrum (although the FCC has expressed some reservations that it still uses too much).

Intersil versos TI

Predictably, 802.11g incorporates parts of both the existing WiFi standard and its faster .11a cousin. The expected .11g specification will be frequency-compatible with the WiFi standard while allowing speeds to scale to 54Mbps in the 2.4GHz band. (802.11a and .11b use different frequencies and hence can operate side-by-side but currently cannot interoperate.)

802.11g has two "mandatory" modes of operation: OFDM (offering 802.11 a data rates in the 2.4GHz band) and implementation of 802.11b Complementary Code Keying (CCK) for backward compatibility with WiFi. Much of the debate surrounding the new specification was centered oil whether it would incorporate OFDM technology from Intersil Corp. or PBCC (Packet Binary Convolution Coding) from Texas Instruments. TI has spent tens (some say hundreds) of millions of dollars developing PBCC technology or acquiring companies who had it.

While TI's technology will in fact be in the 802.11g specification, it is relegated to an optional mode, of which there are two: PBCC-22 (for 22Mbps operation) and CCK-OFDM, to support rates up to 54Mbps. Because the company's existing ACX 100 wireless products already use TI's proprietary PBCC technology at 22Mbps, the company had hoped that its customers' equipment would be able to interoperate at high data rates with future devices from other manufacturers. This now seems less likely.