A Very VSB Vegas

It's one of those good-news/ bad-news things. The good news is that, at the NAB Show this week, Linx Electronics and Microsoft will demonstrate VSB-based transmission of HDTV images to mobile devices. The bad news is that the VSB system is incompatible with the ATSC 8-VSB standard.

Nonetheless, Bob Rast, president of Linx Electronics, whose truck roaming Las Vegas will actually receive the signal, believes the development will silence the remaining holdouts that consider COFDM the superior transmission method because of its mobile applications. And given that a station owned by Sinclair Broadcasting—COFDM's most ardent supporter—is taking part in the demonstration, he may be right.

"The idea that it's a VSB-derived system that would provide for mobile and portable reception fascinated us," says Sinclair technology chief Nat Ostroff. "So I'll be taking one of the first rides on the van myself."

Rast says Linx co-developed an 8-MHz offset-QAM mobile receiver for the Chinese market. South American broadcasters also want a DTV standard that allows for mobile applications so Linx created a 6-MHz VSB version that can receive HD signals.

The demonstration will provide mobile transmission with a payload of 9 Mb/s, in what is also referred to as 2-VSB half-rate mode (8-VSB is full-rate, 19 Mb/s). The signal will originate from KFBT-DT Las Vegas, using Tandberg's Windows Media 9 encoder to encode the content in the Windows Media 9 format before transmission via an Acrodyne high-power UHF transmitter. During the test, current receivers in the Las Vegas market will be unable to receive the signal.

"The 2-VSB mode is not in the existing standard, and therefore current receivers do not receive them," says Rast. "The 2-VSB mode would have to be added to the standard, and the proposal would include the ability to do mixed modes, so that, within a single transmission, one can do more than one of the modes."

Rast adds that receiving mobile is the most demanding reception situation, with heavy time-varying multipath concerns. The issue is how the signal is acquired, synchronized and equalized with changing multipath conditions. The Linx receiver handles those issues, and Rast says it could be licensed by consumer-electronics manufacturers.

He says 2-VSB is more suitable for mobile applications because it can deal more easily with the multipath issues. The ATSC is working on an enhancement of 8-VSB, the spec expected to be available this summer.

"The enhancement of 8-VSB will have additional coding on the transmission and receiver sides, and the result allows a lower noise threshold, enabling reception of weaker signals," Rast explains. "But that does not benefit the equalization, which means that the performance in the presence of heavy multipath is not improved. The 2-VSB system lowers the threshold and is easier to equalize."

The mobile system, he adds, could become a new ATSC standard, which could include "normative references" to existing ATSC standards. That would create a new consistent standard, which would allow ATSC 8-VSB receivers to also include a mobile capability.

The use of Microsoft's Windows Media 9 format recalls the promise of the codec when it was first demonstrated as Microsoft's Corona system. The format can reduce the payload of HDTV content and the 5.1 Surround Sound audio to as low as 6 Mb/s. The SD load to be demonstrated at NAB can be handled at 1.5 Mb/s. Tandberg's Windows Media 9 encoder will be used in the demonstration to insert the content into the broadcast signal.

"If you're a broadcaster, strategically, you want to reach out to people who aren't on cable's tether," says Mike Aldridge, lead product manager for the Windows Digital Media division. "This can provide video and data to devices like computers, TVs or a hybrid. It's another missing piece to what broadcasters can do with the new capacity."

Regarding use of the standard here in the states, Rast says it's a sensitive issue because transition is picking up steam. "As soon as people start talking about tampering with the standards and obsoleting receivers, it has the risk of slowing down the transition. And there are a number of broadcasters who have no interest in slowing down the transition. But there are others who want mobile."

A wider audience

One of those broadcasters is Sinclair. Ostroff says Sinclair believes that anything that demonstrates the capability of digital transmission to reach a wider audience is of interest. Three years ago, the company was involved with a demonstration of mobile transmission using the DVB standard at an 18-Mb/s data rate. This year's demonstration will replicate that one but with a system that requires only 9 Mb/s.

"The great price that broadcasters seem willing to pay," he says, "is to give up simple indoor-antenna reception, mobile reception and portability, and the business opportunities that arise out of all of that."

Noting the example set by the cable industry, which constantly updates its capabilities and set-top boxes to remain current with technology, Ostroff wonders why the broadcast industry doesn't want the same flexibility with its digital standards.

"Why is the broadcast industry willing to tie itself to a 15-year-old technology like VSB" he asks, "and offer no upward mobility of technology because we have to remain compatible with a fraction of a percent of the total number of receivers in consumer's hands?"

Very long term

While there is no opportunity for broadcasters to take advantage of the new technology anytime soon, it isn't ruled out for the future. ATSC President Mark Richer is interested in the demo, but, he says, the lack of backwards compatibility is a problem here in the U.S. "That isn't to say there couldn't be a migration path to it in the very long term. But, if you switch to that mode today, you can't provide programming to existing receivers or stuff in the pipeline."

With ATSC working on its own combatible enhancement of 8-VSB, long term could become very long term. But the demonstration could lay the groundwork for one of those "told you so" moments.

"I'm hopeful," says Ostroff, "that, when broadcasters see millions of automobiles built with TVs in the back seat and people in Europe receiving signals on cellphones and PDAs, someone will remember that, at NAB 2003, there was a demonstration of mobile and portability applications."