WASHINGTON In response to broadcasters' calls for flexible use of digital TV spectrum, the Advanced Television Systems Committee unanimously agreed on Wednesday (June 28) to explore "enhancements" to the vestigial-sideband modulation scheme that lies at the core of its U.S. DTV standard. The decision could open the door to variations that may not be backward-compatible with the current approach, which is known as 8-VSB.
OEMs are treading carefully since Wednesday's decision, downplaying the possibility that DTV products built around the 8-VSB standard will swiftly be made obsolete.
"We support any and all improvements in reception capabilities in the ATSC standard," said John Abel, vice president of business development for Geocast Network Systems (Menlo Park, Calif.), which has already developed a set-top box for datacasting that uses 8-VSB. "We welcome the initiative to enhance reception on portable and mobile devices, as it will enable delivery to multiple platforms."
Privately, however, some industry insiders voiced concerns that tweaking the DTV modulation spec now could set U.S. OEMs' product plans awry.
Meanwhile, receiver maker Zenith is touting a pair of possible VSB enhancements that the company will likely submit to the ATSC. "The ATSC's decision validates our claim that VSB has enough flexibility and headroom for further improvements," said Richard Lewis, senior vice president of research and technology at Zenith Electronics Corp. (Glenview, Ill.).
At the same time, chip maker NxtWave Communications Inc. (Langhorne, Pa.) said it had silicon solutions for 8-VSB in the works. Matt Miller, president and chief executive officer at the company, called the ATSC's move to reopen the 8-VSB debate "a rational approach." Making enhancements "within a framework of the existing standard" is the right way to go, Miller said.
ATSC's executive committee decided "it's a good idea to pursue enhancements to the 8-VSB scheme and we want to expedite it," Mark Richer, ATSC's executive director, said this past week. "Most people are focused on backward compatibility, but there is no limitation" on enhancements that aren't compatible, Richer added.
At issue are growing requirements among some broadcasters including NBC and Walt Disney Co./ABC for two improvements in the U.S. digital television specification: better reception, particularly in certain urban areas; and a modulation scheme capable of broadcasting both video and data to mobile communicators and other portable equipment. Many in the industry believe 8-VSB is unsuitable for mobile applications.
Indeed, mobile applications will "require some modification of the 8-VSB standard," the ATSC's Richer said.
Wednesday's action focuses solely on enhancing the existing VSB modulation scheme to improve digital TV video reception for fixed as well as mobile devices, Richer said. The move is separate from an ATSC task force study on an alternative modulation scheme called coded orthogonal frequency-division multiplexing (COFDM) that some broadcasters favor.
It's not clear whether the ATSC's decision to pump up VSB indicates an effort to fend off a more radical move to COFDM, or is the start of a broader reconsideration of DTV modulation.
Sinclair Broadcasting, which has spearheaded efforts to shoehorn COFDM modulation into the U.S. digital TV standard, said it would work with ATSC on the VSB enhancement effort. "We have every intention of participating in the hope that this isn't a cynical attempt to buy time," said Nat Ostroff, vice president for new technology at Sinclair (Hunt Valley, Md.).
VSB proponents said they are already developing a road map for extending today's 8-VSB scheme to respond to broadcasters' cry for better reception and their new requirements for mobile services. Lewis said that when Zenith first introduced VSB more than 10 years ago, it laid out options for a variety of modulation flavors, from 2-VSB, 4-VSB and 8-VSB up to 16-VSB.
As with any data transmission, vestigial-sideband modulation requires a trade-off between bit rate and robustness, said Lewis. At a time when cell phones can deliver data at 14 kbits/second, 8-VSB offers a bit rate of 19 Mbits/s. Meanwhile, 2-VSB could offer about 10 Mbits/s, Lewis added.
To address the need for better TV reception, especially in crowded urban areas where signals encounter a lot of interference, Zenith hopes to propose a so-called "bi-hierarchical" approach. In the scheme Zenith calls "R-VSB (Bi-rate)," 2-VSB signals are embedded inside an 8-VSB stream.
The key to R-VSB is that it maintains backward compatibility, Lewis said. In essence, a current-generation DTV receiver will demodulate only the 8-VSB portions of a birate signal and ignore the 2-VSB information. Future systems built around a 2-VSB/8-VSB chip would be able to pull out special data embedded inside the 2-VSB portion. It will be up to broadcasters to decide how much information they want to carry in 2-VSB and 8-VSB, Lewis said.
Zenith claims it has already discussed such a proposal with VSB competitors such as Motorola Inc. and semiconductor startup NxtWave Communications. Asked how much of the bi-hierarchical approach has been proven, Lewis said, "Parts of it have been demonstrated." Details of the technology will be submitted to the ATSC's request for proposal for 8-VSB enhancements, he added.
Zenith estimates that a 2-VSB/8-VSB chip can be developed by the end of 2001, putting the likely time frame for improved DTV sets out to 2002.
Several industry observers said the 2-VSB approach has technical merit but predicted it would be very difficult to make 2-VSB extensions to the ATSC spec backward compatible with 8-VSB. Some argued that it will take at least two years before a 2-VSB extension arrives that can win ratification by the full ATSC membership. And without ratification, these industry players noted, no manufacturer would offer silicon.
If that scenario plays out, it means nearly all DTV receivers sold today and in the next several years will not be able to receive 2-VSB-based broadcasts.
If mobile datacasting, rather than videocasting, is what the broadcasting industry wants, "We are preparing to offer yet another modulation scheme, called M-VSB," said Lewis. Although M-VSB is a member of vestigial-sideband modulation family, it is a special mode designed for a smaller 5-Mbit/s pipe and won't be backward compatible with the current 8-VSB spec, he added.
Still other alternatives are in the wind. NxtWave's Miller claimed that his company has its own intellectual property that could make "mobile applications feasible" within the 8-VSB modulation scheme. "But first," Miller said, "the industry has to build a consensus" on what sort of mobile applications it is looking for. "It's got to be specified. We can't build a chip in accordance to 60 different broadcasters' applications," he said.
Meanwhile, a political battle may mushroom from the technical one. That's because the push among TV broadcasters to position themselves and their free spectrum for mobile multimedia assuming government regulators let them do so comes as cellular phone service providers face potentially pricey auctions for 700 MHz of spectrum they will need to deliver their third-generation data and multimedia services.
"These guys are buying their spectrum at auction," said Gerry Kaufhold, principal analyst for Cahners In-Stat Group, speaking of the telecom service providers. "I don't think they're going to be really pleased if broadcasters decide to abdicate their main mission delivering TV entertainment and instead decide to try to steal mobile data services from the cell phone industry."