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All Hail OFDMA!

WiMax and 3G might be bloodthirsty competitors, but they’re moving to common ground, says BT honcho

September 9, 2005

3 Min Read
All Hail OFDMA!

OFDMA (orthogonal frequency division multiple access) is emerging as the clear choice for thenext-generation radio interface in mobile wirelessnetworks, said Mick Reeve, group technology officer atBTGroup plc (NYSE: BT; London: BTA), in his keynoteat Light Reading’s Future of Telecom Europeevent in London yesterday.

Reeve said that “almost everyone agrees” OFDMA willbe the next major evolution in mobile wirelesstechnology, but he noted there are unanswered questions abouthow, when, and by whom it will be implemented.

“Mobile guys are saying it’s just an enhancement to 3G,and WiMax guys are saying it’s WiMax,” said Reeve.“We’ve seen agreement on technology, but there’s alack of clarity on standards and spectrum.”

OFDM works by dividing a given spectrum block into a numberof sub-channels, each of which is individuallymodulated and then transmitted orthogonally tominimize interference with one another.

The result is faster, more robust radio links than canbe achieved with alternative modulation/multiplexingschemes. It is often claimed, for example, that OFDMis more efficient, in terms of bits per Hertz, thanCDMA and WCDMA (wideband code division multipleaccess) technology used in 3G systems, and/or deliversbetter performance in non-line-of-sight urbanenvironments due to better resistance to multipath interference.

For these reasons OFDM has been adopted as the radiointerface for 802.11g and 802.11a (but not 802.11b),for digital TV broadcast systems such as Digital Video Broadcast (DVB), and for Fixed WiMax systems based on the 802.16-2004 standards. Now the adoption of OFDM in more demanding cellular systems is starting to have an impact on the mobile infrastructure market.

Specifically, the demands of mobility and two-way communications are pushing the industry towards a variant of OFDM called OFDMA , which can assign a subset of sub-carriers to individual users. This is the radio interface being adopted by Mobile WiMax, via the upcoming 802.16e specifications, and being implemented in the Korean WiBro equipment.

For non-line-of-sight applications, OFDMA is nowconsidered superior to the 256-carrier OFDM specifiedby the Fixed WiMax 802.16-2004 standards to the extentthat some in the industry (mainly those not buriedunder a mountain of time and money sunk into FixedWiMax) believe that fixed wireless broadband accesswill, in fact, become just an application of MobileWiMax, due to its superior physical layer andanticipated higher unit volumes.

The OFDM physical layer is also being developed bymobile system providers currently outside the WiMaxsphere. At this point, terminology gets seriouslyconfusing and the stakes get even higher.

QualcommInc.’s (Nasdaq: QCOM) recent $600 millionacquisition of FlarionTechnologies for its “FLASH-OFDM” technology waswidely seen as public recognition by Qualcomm that itsCDMA hegemony is under long-term threat from newerOFDMA systems. Interestingly, in its announcement ofthe acquisition, Qualcomm employed OFDMA terminology, eventhough Flarion had not previously used the termpublicly.

Meanwhile OFDMA pioneers, such as AdaptixInc., are working to differentiate themselves bypresenting their technology as OFDMA/TDD -- which worksby assigning sub channels to individual usersdynamically in time. (See Adaptix, NY3G Team Up ).

There is also a widespread expectation that OFDMA willbe adopted by the 3rd Generation Partnership Project (3GPP) through its Long Term Evolution (3G LTE) working group, also referred to as “Super 3G.” The difference here is that it’s likely to be several years until anything much happens. This is because the world’s 3G systems providers and operators have more pressing issues to deal with, including implementation of HSPA (High Speed Packet Access) and EV-DO Rev A radio interface upgrades.

— Gabriel Brown, Chief Analyst, UnstrungInsider

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