In the last few years, orthogonal frequency division multiplexing access vendors made quite a splash, promising high-capacity, mobile broadband access well ahead of when WiMAX and 3G services were expected to be available. However, more recently, that hype has died off. After Qualcomm announced its acquisition of OFDMA's biggest booster — the former Bell Labs spinoff Flarion Technologies — in August 2005, the relentless push to commercialize OFDMA as a proprietary technology has ceased.

Why? OFDM pioneer Adaptix has a simple answer: standards. OFDM technologies have been so readily embraced by the standards bodies for both the broadband wireless access industry and the cellular industry, that pursuing the technology independently of the WiMAX Forum or the two major 3G standards bodies — 3GPP and 3GPP2 — is pointless, said Mike Pisterzi, CEO of Adaptix.

OFDM was implicit in the 802.16-2004 standard that created the foundation for Fixed WiMAX, and OFDMA was written into the 802.16e specification ratified last December by the IEEE and will pave the way for Mobile WiMAX solutions.

“OFDMA is mandatory in the 802.16e standard — it's actually S-OFDMA, or scalable OFDMA,” said Paul Sergeant, senior marketing manager for alternative access for Motorola. “So, we are doing OFDMA, and we're all doing it, and it is also one of the reasons why 802.16e is not directly backward compatible to 802.16-2004.”

Although many products based on the 802.16e standard are still in the developmental phases, Adaptix has its own second-generation OFDMA Motion product line available with deployments in Asia. However, it's betting the farm on its upcoming release of its third-generation technology, designed to meet the guidelines that have been laid out for Mobile WiMAX and the IEEE's 802.16e standard. The potential for Mobile WiMAX is simply enormous, with potential profiles from the WiMAX Forum targeting the 2.5 GHz and 3.5 GHz frequencies that are available and in use in many countries worldwide, as well as 2.3 GHz and other frequencies. Those initial WiMAX Forum profiles also will cover a wide range of bandwidth channel specifications, including 5 MHz, 7 MHz, 8.75 MHz and 10 MHz.

To continue to target niche markets with proprietary technology makes little sense, if a standardized version of that technology would grab the mass markets as well as niches, too, Pisterzi said. “If a vendor is comfortable with a non-standard technology and a small customer base, that's fine,” Pisterzi said. “But the industry as a whole is moving toward standardization.”

Though often mistaken for one another, OFDM and OFDMA are actually two different variants of the same technology. Both divide one extremely “fast” signal into numerous “slow” signals, each spaced apart at precise frequencies. The advantage here is that those individual slow signals, or subcarriers, aren't subject to the same intensity of multipath distortion faced by a single-carrier transmission — the data is traveling slowly enough that the effects of the distortion become negligible. The numerous subcarriers are then collected at the receiver and recombined to form one high-speed transmission.

The difference between OFDM and OFDMA is that OFDMA has the ability to dynamically assign a subset of those subcarriers to individual users, attuning the technology to the particular demands of mobility. Thus, OFDM technologies occupy nomadic, fixed and one-way transmission standards, ranging from TV transmission to Wi-Fi as well as well as Fixed WiMAX and newer multicast wireless systems like Qualcomm's Forward Link Only (FLO). OFDMA, however, adds true mobility to the mix, forming the backbone of Mobile WiMAX and the 3GPP's new standards for 3G long-term evolution (LTE). Furthermore, S-OFDMA allows for an increase in range of channel bandwidths from 1.25 MHz up to 20 MHz.

“Mobile WiMAX, or 802.16-2005, is really misnamed,” said Mark Whitton, vice president and general manager for WiMAX at Nortel Networks. “802.16-2005 is an ideal solution for mobile, portable and fixed implementations of WiMAX, and it is essentially a superset of 802.16-2004, with significant performance advances like MIMO and scalable OFDMA.”

On the 3G side, the 3GPP recently finalized the initial list of requirements for 3G mobility and coined the term LTE. The preliminary specs call for a complete shift in 3G standards away from wideband-CDMA to OFDM, meaning the future of wireless technology and its billions of users is headed in OFDMA's direction. Cellular system vendors have jumped all over the new specifications, shoehorning years of research in OFDM and related technologies like multiple input/multiple output (MIMO) and smart beam forming into the new standards track.

“Where conventional smart antenna systems deliver performance gains by adding complex, costly and bulky equipment to the tower top, MIMO takes advantage of smaller and simpler changes in both the devices and the infrastructure to deliver performance improvements well beyond what even the most complicated smart antennas can deliver,” Whitton said.

Nortel unveiled its LTE product line, called high-speed OFDM packet access (HSOPA) at the 3GSM World Congress in Cannes, France in February. The platform is intended to pick up where the latest UMTS uplink and downlink upgrades leave off. Nortel already plans to have a prototype built by the end of the year, ready for lab tests, and carrier trial equipment ready by 2007. Qualcomm is pursuing both OFDM and OFDMA, using OFDM for its multicast technologies and in its pursuit of the 802.11n standard for the evolution of wireless LAN. And with its $600 million acquisition of Flarion completed in January, Qualcomm is lending the weight of its $1 billion annual R&D budget to further development of Flarion's OFDMA technology toward the IEEE 802.20 standard, a broadband wireless technology that not only has mobility but really fast mobility (the typical example is that of a user maintaining a constant data connection while riding a bullet train).

As for Flarion's Flash OFDMA technology, Qualcomm isn't quite so definite. Jeff Belk, Qualcomm senior vice president of marketing, said the vendor will continue to support the existing product line and its existing customers but offered no insight as to whether it would continue to pursue the portfolio or simply wrap the technology up in its other OFDMA efforts. Regardless of Flash's future as product line, Qualcomm is definitely gung-ho on the underlying technology itself.

“Qualcomm has the scale to examine a broad range of technologies,” Belk said. “We're not committing to just one product.”