Commentary: WiMax and Wi-Fi: Separate and Unequal

The important but widely misunderstood IEEE 802.16 standard

4 min read

Illustration: CSA

To judge from what's appearing in the trade and business press lately, WiMax is hot, hot, hot. Certainly the technology, based on the relatively new IEEE 802.16 standard, is a great idea: radios atop buildings and towers would feed Internet access, at broadband speeds, directly to individual users via cards or radios attached to their computers, up to 50 kilometers away.

But members of the press have, by and large, misunderstood WiMax's goals and markets. "Think of it as Wi-Fi on steroids," Business Week recently enthused. The Washington Post , in a story under the headline "Wi-Fi Expands," similarly confused the two standards. "The technology will grow more powerful, too, as a type known as WiMax that sends signals up to 30 miles hits the field," the paper reported.

WiMax, in fact, is not a Wi-Fi extension. Wi-Fi is a local-area networking standard developed by the IEEE 802.11 working group and is designed to be used indoors at close range, to distribute Internet access to a bunch of computers in a home or an office. WiMax, on the other hand, is a wireless replacement for a wired broadband connection. That is, it's a new way to get Internet access into the home or office in the first place, and to do so more cheaply and easily than through the wires of telephone companies or cable providers [see "The Wireless Last Mile," IEEE Spectrum, September 2003, pp. 18-22]. In a typical home scenario, a WiMax receiver providing Internet access would be connected to a Wi-Fi router that ties together all of a household's computers.

The two standards use different chip sets and different schemes for quality of service and security. They may or may not operate in the same regions of the radio spectrum. Most important, they operate with different assumptions about the radio environments in which they work.

Compounding the misunderstanding is an extension to Wi-Fi that is in the works. The added feature is championed by a new IEEE standards task group, 802.11n, created last September. Its goal is an amendment to 802.11 primarily intended to increase Wi-Fi's data rate to over 100 megabits per second. That is five times the speed of the relatively new 802.11g standard and a mind-bending 17 to 20 times the speed of 802.11b, the version most Wi-Fi devices use today.

Some wireless enthusiasts think that a higher speed for Wi-Fi isn't the way to go. Because in radio technologies there's typically a tradeoff between data rates and distance, they have speculated that by toning down IEEE 802.11n's speed, they can increase its range to make it, too, a DSL competitor for the last mile.

Nevertheless, those involved in the development of Wi-Fi and WiMax believe that competition between the two will be minimal, largely because they operate completely differently at what network engineers call the media access control layer--that is, the manner in which two devices find one another and communicate across a physical network.

In a Wi-Fi, devices are omnidirectional, finding access points wherever they are, while 802.16 WiMax devices typically face an access point, usually called a base station. Users of Wi-Fi devices are expected to hear each other and defer transmission if the network is busy. In contrast, the WiMax control protocol requires that users transmit only when instructed to by the base station.

These differences make WiMax ideal for a fixed point-to-multipoint network that lets hundreds, or even thousands, of users connect to the Internet from a central access point atop a tower, says Roger Marks, chair of the IEEE's 802.16 working group. But WiMax would be inappropriate for a local-area network, where a user needs to be able to carry a laptop or PDA into a conference room without losing a network connection.

Stuart Kerry, chair of the IEEE working group for 802.11, says that it's more likely that laptops and PDAs would be built with chip sets for both standards, in much the same way that dual- and tri-band cellphones accommodate different cellular protocols.

In fact, yet another budding IEEE standard devoted to handoffs, 802.21, would let users maintain a connection across not just different networks but different types of networks. You could, for example, keep watching a news story on your wireless PDA as you left a Starbucks Wi-Fi hotspot, automatically transferring to your provider's WiMax or cellular data network. That would, though, require adding mobility to the current standard, something the 802.16 committee has in mind.

The more immediate task for the 802.16 group is finalizing standards for conformance testing, to ensure that an access device made by one manufacturer will communicate with a computer equipped with a device from another. Then the WiMax Forum has to follow through on its announced intention to implement those conformance standards. Without them in place, a WiMax market would take a decade or more to develop--an impossibly glacial time frame for a telecommunications technology.

Even less ready for prime time is 802.11n. Its task group met in mid-January to rejigger its schedule and elect a new chair, Bruce Kraemer, senior manager of strategic marketing for GlobespanVirata Inc., a Red Bank, N.J., fabless manufacturer of telecommunications chip sets. Kraemer told Spectrum that proposals will first be submitted to the group this summer, and that a standard would probably not be issued until mid-2005 at the earliest. The task group next meets this month in Orlando, Fla.

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