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NAB Convention Features Emerging Technology
John Loughmiller, Contributing Editor -- Design News, April 27, 2009
The week-long National Association of Broadcasters Show in Las Vegas closed on April 23 after showing three new approaches to content distribution using the Advanced Television Systems Committee (ATSC) digital television standard.
Delayed again and again since its inception in the mid 1990s, the "this time we really mean it" date for final cut over to the ATSC 8VSB DTV system is now set for June of this year. Broadcasters are ready to move from the introduction phase to the profit enhancement phase, and to help them along engineers have come up with three emerging technologies. Unfortunately the first is an ode to gadget freaks and the second can't be implemented at all using present technology, which leaves design engineers with only one that has a reasonable chance of making it to the marketplace anytime soon.
Emerging technology number one is 3-D television. A surefire hit with early adopters and video game players, most of the remaining potential viewers can't get past the need for special glasses to view the content. Couple that with the need to transmit two images in the same bandwidth normally used for one and that means a loss of resolution − something that's unacceptable to viewers accustomed to HDTV.
The technology way out on the event horizon is Ultra High Definition Television. Developed by Japan's NHK network, UHDTV features performance at least four times better than Sony's Blu-Ray® 1080p system and it's stunning to see even in prototype form. The problem is the ATSC system only has enough bandwidth for 1080i HDTV signals using its MPEG-2 video compression standard. NHK thinks these problems will be solved by 2020 but without changing the current ATSC 8VSB primary compression methodology it's difficult to see how this will happen. All of this brings us to the remaining emerging technology – one that is ready now, albeit with some challenges. The third technology is Digital Mobile Television and it's already in the testing phase in several markets.
The standard DTV transport scheme uses MPEG-2 compression and has Forward Error Correction (FEC) but can't be made to work reliably in a moving vehicle. Multi-path problems and Doppler shift causes signal cancellation and frequently results in reception at a stop light but not while actually driving. Enter ATSC A/153 (ATSC-M/H), a new encoding subsystem added to the main ATSC transport scheme.
ATSC-M/H is aimed squarely at the cell phone marketplace and other handheld media. Unlike the basic platform, it uses MPEG-4 compression, a robust FEC and a training sequence to negate signal cancellation problems up to 100 mph velocity. ATSC-M/H requires just a 1-2 Mb/sec bit rate to transmit a modified ¼ VGA image of 416x240 pixels plus audio but that still may create a problem. Regular HDTV signals require most of the available bandwidth and broadcasters are already using the remainder for things like local weather radar. How will viewers react if the radar disappears? And will users be able to understand their cell phone is now receiving signals from both the service provider and local TV stations? Who do they call when they have problems with the DTV? On the technical side, how do engineers and designers cope with TV stations using low VHF channels that require much more than a miniscule cell phone antenna for efficient reception and what about intermodulation issues in urban environments?
Still, ATSC-M/H offers a new revenue stream to an industry once thought of as a license to print money. Broadcasters desperately want the revenue so you'll be hearing more about this emerging technology in the near future.
National Association of Broadcasters convention in Las Vegas
