Posted 3/01/2002
Coming Back for More
New Techniques Could Alter Prospects for Fixed Wireless
By Fred Dawson
While AT&T Corp. and Sprint Corp. recently killed development of their fixed broadband wireless initiatives, new technical advances in fixed wireless at the lower frequencies could breathe new life into the ailing technology.
Despite the virtual abandonment of fixed wireless in the United States, demand for broadband in underserved overseas markets is proving to be strong enough to keep the momentum building, along with some help from a bevy of smaller service providers operating in unlicensed and MMDS bands in the United States.
One sign of the changing scenario in fixed wireless access is a decision by Netro Corp., a leading supplier of upper-tier systems in the LMDS range, to purchase technology developed by AT&T Wireless Inc. for applications in the 1.9 and 2.3GHz frequency zones. AT&T Wireless's abandonment of its "Project Angel" deployment was perceived widely as another setback for fixed wireless technology, despite official claims that the decision was driven by strategic considerations having nothing to do with the viability of the technology. Netro's decision to buy the platform following a worldwide search for solutions in the lower frequency areas appears to support that assertion.
"After reviewing many options we have determined that the AT&T Wireless fixed wireless technology is the best platform to meet our market vision," says Gideon Ben-Efraim, Netro chairman and CEO. "The market is clamoring for next-generation solutions that can deliver high-speed data and carrier-class voice service in non-line-of-sight as well as line-of-sight situations." Netro will be offering the platform at the 1.9 and 2.3GHz frequencies right away and is tweaking the platform to operate at the widely licensed 3.5GHz level in markets outside the United States., Efraim says. "We anticipate the 3.5GHz product will take approximately six months to develop."
Netro, which is discussing deployments of the Angel Products line with operators in China and Latin America, anticipates service providers will use the platform in residential and small-business scenarios. Holders of LMDS-type frequencies, meanwhile, could deploy the high-end Netro platform for backhaul between base stations and COs. "This is a field-proven technology that has been deployed in 10 U.S. markets and had close to 50,000 customers before it was terminated," Efraim notes. Netro anticipates by 2003 the Angel Product line will generate 40 percent to 50 percent of the firm's revenue, he adds.
Highlights of the deal, which was to close in mid-February, includes purchase of the technology for $16 million in cash and 8.2 million Netro shares and brings 125 AT&T Wireless engineers and other employees from Project Angel into the Netro fold. AT&T Wireless then will have a 13.5 percent stake in Netro and its executive vice president Lewis Chakrin named to Netro's board. AT&T will be a strategic partner in pursuit of potential projects with the manufacturer, officials say.
The Angel system, like many of the next-generation systems entering the market, uses the orthogonal frequency division multiplexing (OFDM) modulation technique. The technique, which varies modulation levels at different subcarrier frequencies within a given bandwidth channel to maximize transmission efficiency, goes a long way toward dealing with the major impediments to saturation coverage over fixed wireless access systems.
"OFDM solves a lot of problems, including interference between cells," notes Eric Dunn, director of DSP engineering at equipment supplier NextNet Wireless Inc. In mid-January, Dunn told the Wireless Communications Association's technical symposium in San Jose, Calif., that a big reason NextNet chose OFDM for its MMDS system is that it allows frequency reuse when MMDS operators subdivide their territories into smaller cells to maximize the ratio of users to available channel capacity in the frequency-limited spectrum category.
NextNet, whose first commercial deployment is with service provider Evertek Inc. in Northern Iowa, offered proof of its system's robustness at the symposium by demonstrating non-line-of-sight penetration to an in-building receiver on the exhibition show floor in the San Jose Fairmont Hotel from a rooftop antenna mounted atop the nearby Tech Museum of Innovation. "We have eliminated the truck-roll installation, overcome multipath interference and provided consistent LAN-like speeds with extended coverage," said Charles Riggle, vice president of marketing and business development at NextNet.
Several other techniques are in play among suppliers of next-generation systems, including automatic repeat request, which overcomes packet loss congestion in TCP/IP links; mesh topologies, which deal with non-line-of-sight problems by offering several routing paths for signals; TDD, which transmits signals in both directions over the same carrier frequency, and advanced antenna systems such as switched beam, diverse path combining and beam forming.
