Although the development of WiMAX is often compared to Wi-Fi, WiMAX draws a closer parallel to cellular in one respect: spectrum. An ideal cellular phone today would have to operate in at least five frequencies for a decent shot at access to the most services in the United States, Europe and a few other regions. In several years, the list of frequencies that a WiMAX customer device would have to incorporate is even longer, and it might include 2.3 GHz, 2.5 GHz, 3.4 GHz, 3.6 GHz, 5.4 GHz, 5.8 GHz and possibly others such as 700 MHz and 900 MHz.

While the reason for this splintered spectrum approach to WiMAX is rooted in the lack of a suitable global spectrum band, it's also due to an otherwise noble plan set by the developers of the standard. “It's like beauty and the beast,” said Jouni Forsman, a principal analyst for Gartner. “WiMAX was built to be able to approach so many different applications and frequencies, so it's a splintered picture because it can do so much.”

The scattered spectrum environment for WiMAX has some negative repercussions, including that it limits the amount equipment prices can drop and also the potential for interoperability. In the short term, it also means that operators using frequencies other than the initial certifiable bands may not have access to true WiMAX equipment for some time.

Still, many experts are hopeful that these issues will be addressed and the vision of WiMAX-certified equipment becoming available across the spectrum will come to fruition.

“WiMAX is a phenomenon that takes over every band over time, in my opinion,” said Carlton O'Neal, vice president of marketing at Alvarion.

While the range of available frequencies for WiMAX around the globe is wide, two bands hold the most hope for a semi-harmonized approach: 2.5 GHz and 3.5 GHz, both of which have potential in much of the world.

The 2.5 GHz band in Europe is perhaps the most hotly contested of any potential WiMAX frequency. The band was set aside as an expansion band for 3G in Europe and is due to be allocated across the continent by 2008.

“It will be a massive battle,” said Caroline Gabriel, research director at Rethink Research Associates.

3G operators in Europe feel they essentially “prepaid” for the 2.5 GHz spectrum when they bought 2.1 GHz spectrum for 3G, said Margaret LaBrecque, who chairs the WiMAX Forum's regulatory working group and is director of industry programs for Intel's broadband wireless division. They feel it would be unfair for regulators to allow other competitors to pay less for spectrum at 2.5 GHz and compete against them, she said.

The 3G operators are already lobbying hard to ensure that winners of the 2.5 GHz licenses will be able to deploy only 3G or IMT-2000 technologies. “I don't think you can underestimate the sheer lobbying power of Vodafone,” Gabriel said. “The regulators don't upset them lightly.”

Still, the WiMAX Forum is trying to convince regulators in Europe to allow other technologies to be deployed in the band. The European Commission, which represents 25 countries, has said that while it supports harmonization, it doesn't view the 2.5 GHz band as exclusive to 3G services, LaBrecque said.

“The big question is whether the EC will mandate it,” she said. The body could allow individual regulatory bodies to make decisions, or mandate that regulators allow other technologies to be used in the band.

Motorola hopes for one of two scenarios, according to Juan Santiago, director of strategy for Motorola's wireless broadband group. The first is for regulators to make the band completely technology-neutral. However, while regulators in Europe are trending toward liberalizing their spectrum policies, a completely neutral approach would be a break from tradition for most. The other scenario is for WiMAX to be included in the IMT2000 family of technologies, which would mean operators could deploy WiMAX in the 2.5 GHz band.

“We have customers in the UMTS camp, but we'd also like to see WiMAX succeed. We believe they can co-exist,” Santiago said.

The 2.5 GHz band is also being used in some Latin American countries, including Mexico and Brazil as well as some Asian countries and in Lebanon in the Middle East, said Alan Menezes, vice president of marketing for Aperto. In the U.S., the 2.5 GHz spectrum has mostly been consolidated under Sprint, which acquired additional 2.5 GHz spectrum with the Nextel acquisition, and Clearwire.

The other band generating excitement in WiMAX is the 3.5 GHz spectrum. In Europe, operators such as Altitude in France and Iberbanda in Spain are already building broadband wireless networks in the band with the intent of migrating them to certified WiMAX.

While many European countries allow only fixed services in the band, countries such as France, Austria and Ireland allow fixed or mobile in the band. “I expect that to be the exception for the next three years or so,” said LaBrecque. The issue of allowing at least nomadic services in the band has been addressed by almost every regulator in Europe, she said, but they haven't all made the change.

Some operators are particularly excited about the 3.5 GHz band because in many European countries they can receive public funding in rural areas to deploy broadband, and some of them are choosing to do so wirelessly in the 3.5 GHz band.

Outside of Europe, the 3.5 GHz band is also widely distributed, particularly in Latin America and also China. Millicom Argentina and Entel in Chile are both using the 3.5 GHz band and Alvarion gear for future WiMAX networks. In February, Industry Canada auctioned off licenses in the 3.5 GHz and 2.3 GHz bands.

In the U.S., 3.5 GHz isn't available to operators, but the FCC recently opened part of the nearby 3.6 GHz band as a quasi-unlicensed band. While the band is attractive because it overlaps with European efforts to open the same band, the FCC attached caveats that may slow down use of the band. The spectrum is not available near the coasts because it is used there by the military for radar. Users must employ a dynamic frequency selection technique that has yet to be developed to combat interference.

“WiMAX wasn't designed to do that,” Motorola's Santiago said. “There are efforts underway to add that [to the standard], but the concern is how much it will deviate from the standard product.”

In Europe, many regulators are now considering opening the 3.6 GHz band for use by broadband wireless. Leap Broadband in Ireland is already using the band for a network built with Aperto equipment.

“The only issue for us is it's not a WiMAX profile,” said Rory Ardagh, technical director and co-founder of Leap. While Leap expects to see equipment late this year or early next in the 3.6 GHz band that will perform just like certified WiMAX equipment and with a price tag similar to standard WiMAX equipment, the fact that it's not actually WiMAX is an issue.

“It will be a big deal that 3.6 becomes a profile because it will ensure interoperability and remove doubts from the manufacturers that it might not be a band to go into,” Ardagh said.

The unlicensed market around 5 GHz is getting WiMAX attention. The 5.4 GHz band, which is also used on an unlicensed basis in some parts of Europe, was opened up in the U.S. for unlicensed use but has largely gone unused due to an FCC requirement to avoid radar signals transmitted nearby.

“There has been this Catch 22 where the DOD doesn't want to release the radio signatures that the manufacturers require to detect and avoid radar signals,” said Graham Barnes, CEO and founder of NextWeb, the California operator that uses the unlicensed 5.3 GHz and 5.8 GHz bands.

The higher end of the 5 GHz band — the portion around 5.8 GHz widely used in the U.S. — is expected to become more available in Europe, though in some countries the band is used for radar and so will continue to be restricted. Operators in the U.K. and Ireland have been able to use the band, and Leap used the 5.8 MHz unlicensed frequency in Ireland before it acquired the 3.5 GHz spectrum.

The unlicensed environment can be less attractive in Europe and other regions than in the United States, however. Some countries share borders, so the regulators must require very low-power output so that operators won't interfere with the airwaves in neighboring countries.

“In the U.S., satellite radio sits between the 2.3 GHz bands,” Santiago said. “The requirements put on the 2.3 GHz bands to protect that service makes it difficult or expensive to build systems in the band.”

Operators in the U.S. and elsewhere also have been examining the 700 MHz and 900 MHz bands for potential wireless data use. While the bands are ideal for mobility, the data rates they allow would not be as high as some of the other bands.

The fact that broadband wireless networks will be deployed in a variety of frequencies presents some issues for operators that don't have access to the frequencies that the WiMAX Forum will certify.

The first products that will be certified by the WiMAX Forum later this year will operate in the 3.5 GHz spectrum. Users of other frequencies such as the 5 GHz band and the 2.5 GHz band in the U.S. are next in line.

Vendors will make products that operate in other bands, and while the end result is likely to be very similar to WiMAX, the gear won't be interoperable.

“The risk in the short or medium run is that those guys are relegated to making their own business case with proprietary solutions,” said Alvarion's O'Neal. He anticipates a category of products that are WiMAX-like but don't meet the frequency profiles set by the forum and are thus uncertifiable.

In the short term, the array of used frequencies won't affect customer roaming because initial networks will be fixed. But vendors will have to build equipment in a variety of bands to serve operators in different countries, resulting in higher equipment prices. “It's going to limit the price reduction,” NextWeb's Barnes said.

The near term isn't totally bleak for those operators, however. Most vendors insist that they can use many of the same components in all the products so they'll still be able to offer better pricing across the board.

“The downside is that you have to have different radios for each band,” Aperto's Menezes said. The upside is that the chipsets from Intel and Fujitsu, for example, do not include the radio, so vendors can use the same chips in all products. “The big savings is that the chip is a lot cheaper than what most people are using today,” he said.

Experts have mixed feelings about what market impact the splintered spectrum situation for WiMAX might have. Barnes believes prices won't drop as much and WiMAX won't solve part of the problem that has slowed down the broadband wireless market historically.

“The fixed market has not really taken off because it's a segmented market with no clear path to universal adoption of equipment and standards and modes of operating,” he said.

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Nancy Gohring is a freelance writer specializing in wireless and a senior editor at WiMAXNetNews.com.