WiMAX community looks to one-up 3G backers


The IMT-2000 Extension Band, the spectrum between the 2.5 GHz and 2.69 GHz band, has been the subject of much political maneuvering, with 3G backers such as Ericsson looking to preserve it for services such HSDPA and WiMAX advocates wanting to open it up to 802.16e technology.

The WiMAX world scored a victory on the issue late last year, when the International Telecommunication Union declared WiMAX a 3G standard, much to the chagrin of traditional 3G backers. But at least the 3G backers believed they had the upper hand. Their technology operates in FDD mode, or frequency division duplex, signaling with separate channels for the uplink and downlink. WiMAX only uses TDD, or time division duplex, signaling, which assigns time slots for both the uplink and downlink signals.

Those differences are significant because the IMT-2000 Extension Band will more than likely harmonize 2 x 70 MHz for FDD spectrum internationally, leaving 50 MHz for TDD technologies like WiMAX.

Now the WiMAX Forum appears poised to one-up the 3G community. According to a recent article in telecoms.com, the forum is expected to reveal an FDD profile for mobile WiMAX within six months. Paul Senior, chief technology officer of WiMAX vendor Airspan, said the WiMAX Forum has been hush hush about the move because it wanted to get IMT-2000 approval first and avoid the firestorm that an FDD profile would have created.

"... If we had gone to IMT with an FDD profile, we probably couldn't have got it through," Senior said. "We decided to go for something that was a little less threatening, which was a TDD profile. We didn't talk too much about the FDD work which we've been doing for the last 18 months. There will be an FDD profile, it will sit at 2.5GHz FDD allocations just as well as any other technology."

What makes the IMT-2000 Extension Band so important is the opportunity for global frequency harmonization that could help deliver mobile broadband services that interoperate internationally. That, in turn, could create massive economies of scale.

The question is, will the ITU accept an FDD version of WiMAX? Expect a huge political fight over this one.--Lynnette

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