16 IEEE Spectrum | March 2004 | NA

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To judge from what’s appearing in thetrade and business press lately, WiMaxis hot, hot, hot. Certainly the technology,based on the relatively new IEEE 802.16standard, is a great idea: radios atopbuildings and towers would feedInternet access, at broadband speeds,directly to individual users via cards orradios attached to their computers, upto 50 kilometers away.

But members of the press have, byand large, misunderstood WiMax’s goalsand markets. “Think of it as Wi-Fi onsteroids,” Business Week recently en-thused. The Washington Post, in a storyunder the headline “Wi-Fi Expands,”similarly confused the two standards.“The technology will grow more power-ful, too, as a type known as WiMax thatsends signals up to 30 miles hits thefield,” the paper reported.

WiMax, in fact, is not a Wi-Fiextension. Wi-Fi is a local-area network-ing standard developed by the IEEE802.11 working group and is designed tobe used indoors at close range, to distrib-ute Internet access to a bunch of com-puters in a home or an office. WiMax, onthe other hand, is a wireless replacementfor a wired broadband connection. Thatis, it’s a new way to get Internet accessinto the home or office in the first place,and to do so more cheaply and easilythan through the wires of telephonecompanies or cable providers [see “TheWireless Last Mile,” IEEE Spectrum,September 2003, pp. 18–22]. In a typicalhome scenario, a WiMax receiver provid-ing Internet access would be connectedto a Wi-Fi router that ties together all of ahousehold’s computers.

The two standards use different chipsets and different schemes for quality ofservice and security. They may or may notoperate in the same regions of the radiospectrum. Most important, they operatewith different assumptions about theradio environments in which they work.

Compounding the misunderstanding isan extension to Wi-Fi that is in the works.The added feature is championed by anew IEEE standards task group, 802.11n,

created last September. Its goal is anamendment to 802.11 primarily intendedto increase Wi-Fi’s data rate to over 100megabits per second. That is five timesthe speed of the relatively new 802.11gstandard and a mind-bending 17 to 20times the speed of 802.11b, the versionmost Wi-Fi devices use today.

Some wireless enthusiasts think that ahigher speed for Wi-Fi isn’t the way to go.Because in radio technologies there’s typ-ically a tradeoff between data rates anddistance, they have speculated that bytoning down IEEE 802.11n’s speed, theycan increase its range to make it, too, aDSL competitor for the last mile.

Nevertheless, those involved in thedevelopment of Wi-Fi and WiMax believethat competition between the two will beminimal, largely because they operatecompletely differently at what networkengineers call the media access controllayer—that is, the manner in which twodevices find one another and communi-cate across a physical network.

In a Wi-Fi, devices are omnidirectional,finding access points wherever they are,while 802.16 WiMax devices typicallyface an access point, usually called abase station. Users of Wi-Fi devices areexpected to hear each other and defertransmission if the network is busy. In

contrast, the WiMax control protocolrequires that users transmit only wheninstructed to by the base station.

These differences make WiMax idealfor a fixed point–to–multipoint networkthat lets hundreds, or even thousands, ofusers connect to the Internet from acentral access point atop a tower, saysRoger Marks, chair of the IEEE’s 802.16working group. But WiMax would be in-appropriate for a local-area network,where a user needs to be able to carry alaptop or PDA into a conference roomwithout losing a network connection.

Stuart Kerry, chair of the IEEE work-ing group for 802.11, says that it’s morelikely that laptops and PDAs would bebuilt with chip sets for both standards, inmuch the same way that dual- and tri-band cellphones accommodate differentcellular protocols.

In fact, yet another budding IEEEstandard devoted to handoffs, 802.21,would let users maintain a connectionacross not just different networks butdifferent types of networks. You could,for example, keep watching a CNN.comnews story on your wireless PDA as you

left a Starbucks Wi-Fi hotspot, automati-cally transferring to your provider’sWiMax or cellular data network. Thatwould, though, require adding mobility tothe current standard, something the802.16 committee has in mind.

The more immediate task for the802.16 group is finalizing standards forconformance testing, to ensure that anaccess device made by one manufacturerwill communicate with a computerequipped with a device from another.Then the WiMax Forum has to followthrough on its announced intention to im-plement those conformance standards.Without them in place, a WiMax marketwould take a decade or more to develop—an impossibly glacial time frame for atelecommunications technology.

Even less ready for prime time is802.11n. Its task group met in mid-January to rejigger its schedule and electa new chair, Bruce Kraemer, seniormanager of strategic marketing for Globe-spanVirata Inc., a Red Bank, N.J., fablessmanufacturer of telecommunications chipsets. Kraemer told Spectrum that propos-als will first be submitted to the group thissummer, and that a standard would prob-ably not be issued until mid-2005 at theearliest. The task group next meets thismonth in Orlando, Fla.

WiMax and Wi-Fi: Separate and Unequal The important but widely misunderstood IEEE 802.16 standard

BY STEVEN M. CHERRY

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