Sinclair Broadcast Group’s O&O digital terrestrial station KFBT-DT has received an STA to forgo its ATSC 8-VSB digital transmission and provide its digital signal for a 2-VSB mobile HDTV transmission demo for the week of the NAB convention.
The demo, hosted by reception chip maker LINX Electronics and software giant Microsoft, is purportedly being held for a number of South American and Chinese broadcasters who are considering the dual-layered vestigial side band (VSB) modulation system for their countries’ digital transmission system; but when Sinclair gets involved in an over-the-air digital demonstration, criticism of the ATSC’s approved DTV system is usually not far behind.
At NAB2003 participants who register to ride a special van sponsored by Microsoft traveling around Las Vegas, we will see what is being called “the first public demo of Mobile HDTV.”
At NAB2003 participants who register to ride a special van sponsored by Microsoft traveling around Las Vegas, Nev., we will see what is being called “the first public demo of Mobile HDTV.” For the past few months, LINX has performed a similar demo in Chicago, Ill., near the company’s headquarters in Palatine, Ill., with promising results, according to LINX, and others who witnessed the tests.
Proponents of 2-VSB said that while 8-VSB offers multiple levels of signal coverage (called a constellation) that often makes it hard for the decoders to easily identify and lock on a channel, 2-VSB receivers have less information to process and thus are better able to lock on the desired channel under difficult conditions, like when moving in a car.
In Las Vegas, KFBT-DT (on Channel 29's)digital facility will transmit a multiplexed 6 Mbps HDTV (720p) and signal a "live" 1.5 Mb/s SDTV (encoded with TANDBERG hardware) of the KFBT on-air product. According to those close to the demonstration, the 2-VSB datastream will have a total payload of 9 Mbps.
In a letter to the Commission, Sinclair requested and was granted the STA to run from March 24 and end on April 10 with the close of the NAB convention.
Sinclair claims that the system to be demonstrated has identical interference characteristics as the 8-VSB system. The DTV emission envelope and potential impact into other channels and services is exactly the same as an 8-VSB signal. The system also has the same pilot signal, and the radiated power will be identical, according to the application.
The reduced-constellation 2-VSB system provides a more rugged and robust signal than 8-VSB, according to Harvey Arnold, corporate director of engineering at Sinclair, who helped set up the demo. He said, “That’s one of the points of the demonstration. No broadcaster can say they are not interested in mobile reception. If they say that, they have their heads in the sand.”
Arnold said Microsoft approached SpectraRep, a consortium of TV stations that have pooled their spectrum for datacasting services, for the demo, but its membership does not include any Las Vegas stations. Enter Sinclair, owners of KFBT-DT, which was happy to comply.
For the demo, LINX will send a 6 Mhz HD signal at 9 Mbps from KFBT-DT to a van provided by Microsoft, outfitted with mini-theater seating and a 50-inch HDTV plasma display. The mobile HDTV test will use the Windows Media 9 compression system developed by Microsoft, in tandem with KFBT’s Acrodyne (AI) digital transmitter, and a standard rooftop antenna so that the signal can be received in the Microsoft exhibit floor booth (SL136).
The goal for the demo, said Mark Aitken, director of Advanced Technology at Sinclair, is to show broadcasters “interesting extensions for their business in the digital world. There’s recognition that broadcasters need and want mobility [in reception capability],” he said.
As has been its case for the past few years, Sinclair suggests that too much potential revenue for patent holders of 8-VSB technology is at stake for the industry to change the standard now, even if it is flawed in many parts of the country.
“What’s being shown [at NAB] is that the holdup to being able to support mobility is the [ATSC] standard,” said Aitken. “It’s not the technology and it’s not VSB. The process of enhancements that have been run through the ATSC have been put into a straightjacket because backwards-compatibility was one of the requirements. Outside of minimal reception improvements being achieved within lower signal noise environments, there’s been no progress being made in enhancing the 8-VSB system because backwards-compatibility ensures that it can’t happen.”
The demo will also show that Microsoft’s vision for IP-based broadcasting, that is based on Windows Media 9 encapsulated media files, enables new ways to reach reception platforms other than the television, such as the home PC and wireless laptop computers.
In the real world, the technical hurdles of implementing the 2-VSB system would not be insurmountable — as both modulation systems share the VSB architecture. However, if the 2-VSB system were to be adopted by U.S. broadcasters, nearly 500,000 deployed set top boxes that can now receive an 8-VSB signal would not work. “We say, it’s only half a million, so if we’re going to make a change, there’s still time,” Aitken said.
Back in the mid-80s, Philips developed a 2-VSB system that was considered by the ATSC when it was designing the current DTV standard, but it proved unsuccessful for mobile reception and was dropped from consideration in the final standard. Sinclair claims the complex 8-VSB modulation architecture was (and still is) to blame.
For more information, visit www.linxelectronics.com and www.microsoft.com.
