Mobile WiMAX: TDD Now, FDD Soon?  

The frequency division duplex (FDD) version of mobile WiMax has taken a big step toward approval by the WiMAX Forum, Unstrung has learned.

According to documents seen by Unstrung, a recommendation for an FDD profile for three different frequency bands was made to the WiMAX Forum’s technical working group at a meeting last week.

The document specifies the following frequency bands for the FDD profile: the 2.496GHz to 2.690GHz band; the AWS band; and the 700MHz band.

Within those frequency bands, channel bandwidths were also proposed. In the 2.496GHz – 2.690GHz and the AWS bands, the recommended bandwidths are 2×5 MHz and 2×10 MHz. In the 700GHz band, there are three recommended channel bandwidths.

Current mobile WiMax technology is based on time division duplex (TDD), but the available TDD spectrum is limited. Having an FDD version would make the mobile broadband air interface eligible to be deployed in much more of the world’s available spectrum.

Meanwhile, Mobile WiMax (WiBro) is being introduced in major South Korean cities this year using their strictly TDD system in the 2.3 GHz band.

Korea Telecom plans to have 400,000 WiMax subscribers by the end of this year but a limited choice of WiMax gadgets is holding them back. So far there are a total of 18 WiMax products from KT — 10 modems, three mobile phones, and five portable PCs.

SK Telecom, the largest mobile operator in Korea, is another WiMax operator in Korea. But in a recent conference call with investors, the company said it would not make much investment in the business in the near future. The decision will virtually leave KT the lone operator of WiMax for some time.

Additional DailyWireless stories on WiMAX FDD include: WiMAX Uncloaks FDD and Xohm “Partners”.

Clearwire’s Mobile WiMAX coverage in Hillsboro (below) does not yet extend into downtown Portland, Oregon, where the DailyWireless tower is located. explains that alpha tests are being conducted over a 12 square mile region around Hillsboro, which is heavily populated by Intel facilities. This coverage was expanded for the beta tests to encompass the neighboring communities of Aloha and Beaverton, west of Portland, for approximately 145 square miles.

At launch, later this spring, Clearwire expects to cover all of metropolitan Portland and extend into Washington State across the Columbia River into Vancouver USA and parts of Clark County.

Clearwire CTO John Saw says 30-60 Mbps per site will be necessary to meet the demands of all-IP networks, reports Clearwire expects to launch true Mobile WiMAX service in Portland, Las Vegas, Grand Rapids and Atlanta in 2008.

Although it’s idle spectulation, let’s do a very rough comparison of infrastructure requirements between Mobile WiMAX (at 2.5 GHz), unlicensed Wi-Fi and Mobile WiMAX (at 700MHz).

  • Clearwire’s Mobile WiMax in Hillsboro covers 145 Square Miles with 35 to 45 towers.
  • MetroFi in Portland uses roughly 25 nodes per square mile (in a 5×5 array). Twenty five nodes times 145 sq miles equals 3,625 WiFi nodes (don’t forget the backhaul).
  • But 700MHz requires only about 1/3rd the number of towers required by 2.5 GHz WiMAX. Perhaps fewer than a dozen towers would cover the same 145 square miles.

If Verizon wins the 700MHz spectrum, they won’t undercut their cellular business — open platform or not. If Google wins the spectrum, it would be a whole new ballgame — with infrastructure costs one-tenth that of competing 3G cellular and a revenue stream to boot.

Verizon can’t afford to let that happen.

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