WiMax Gets ITU Standards Boost

The International Telecommunication Union (ITU) looks set to approve WiMax as an official radio interface, opening up the possibility that it could become an approved 4G technology and benefit from the upcoming IMT-2000 Extension Band spectrum allocations. (See ITU Recommends WiMax Approval and Spectrum up for Grabs in Europe.)

At a meeting in Japan last week, an ITU Radiocommunication (ITU-R) Sector Working Party recommended that a specific subset of WiMax -- given the catchy, roll-off-the-tongue moniker of "OFDMA TDD WMAN" -- should be approved as an IMT-2000 radio technology alongside classic 3G systems.

ITU approval would ease access to spectrum for WiMax operators and would position the technology for participation in the ITU's IMT Advanced process that aspires to define 4G wireless by 2009, ahead of deployment in 2011.

Although final approval is still some way off and is not guaranteed, the move is significant because some wireless companies and regulators had wanted to restrict official ITU status to technologies within the 3G roadmap. Such a restriction could lock WiMax out of future spectrum allocations in favor of orthogonal frequency division multiple access (OFDMA) systems based around the 3rd Generation Partnership Project (3GPP) 's Long Term Evolution (LTE) initiative or the 3rd Generation Partnership Project 2 (3GPP2) 's Ultra Mobile Broadband (UMB).

For years access to the IMT-2000 Extension Band (between 2.5 GHz and 2.69 GHz) has been subject to intense political and technical lobbying, with the entrenched interests of the 3G community coming into conflict with backers of up-and-coming WiMax technology.

Aside from raw spectrum, what makes the 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 economies of scale not seen since Europe rallied around GSM in the late 1980s and early 1990s.

Current thinking is that IMT-2000 Extension Band will seek to harmonize 2x70 MHz of Frequency Division Duplex (FDD) spectrum internationally, leaving 50 MHz (less guard band) that could be allocated to Time Division Duplex (TDD) technologies on a national basis between 2.57 GHz and 2.62 GHz. Such an outcome would still heavily favor the 3G roadmap, which is focused on FDD systems.

For those who dozed off in wireless school, FDD systems send and receive information in separate frequency bands, while TDD systems send and receive information in the same band at different times. There are pros and cons to both.

WiMax companies have the option of developing FDD systems, but at this point it's not clear many would want to go down that route. Nearly all the near-term focus and public attention is on TDD systems, such as the mobile WiMax network being deployed by Sprint Corp. (NYSE: S). Privately, however, some major WiMax backers acknowledge that FDD systems may be required in order to remain competitive. (See Sprint & Nokia's 10 Gallon WiMax and Sprint Facing WiMax Delays?.)

One thing is sure -- the debate between the respective spectral efficiencies and network economics of TDD and FDD technology is ramping up. Classic mobile networks are all based around FDD, which is used because it enables better link budgets (and therefore larger cell sizes and fewer base stations) and is deemed more reliable. TDD, on the other hand, is considered more spectrally efficient for asymmetric data applications, such as might be served on WiMax networks.

Speaking in a recent Unstrung TV interview, Ericsson AB (Nasdaq: ERIC) CTO Hakan Eriksson came down heavily in favor of FDD, saying it's no surprise that 90 percent of spectrum in the world is allocated to FDD systems and only 10 percent to TDD. "FDD is a better way of utilizing spectrum than TDD," said Eriksson. "TDD is more of an emergency solution. If you only have one band, then you have to do it. If you can, you always try to avoid TDD."

To watch the "Eriksson of Ericsson" interview in full, click here.

TDD versus FDD is clearly a touchy subject. In its original submission to the ITU, the Institute of Electrical and Electronics Engineers Inc. (IEEE) used the term "IP-OFDMA" to describe WiMax, perhaps in an attempt to tone down the TDD nature of the technology, and was backed in its lobbying efforts by the WiMAX Forum .

On hearing the ITU had decided to call it OFDMA TDD WMAN, Roger Marks, chair of the IEEE 802.16 Working Group responsible for WiMax standardization, noted in a message to the 802.16 community that this is a "compromise name."

The concern in the WiMax camp will likely be that, despite this latest standards fillip, all the best spectrum will be reserved for systems within the 3G roadmap.

— Gabriel Brown, Chief Analyst, Unstrung Insider

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