ATSC Task Force To Scrutinize DTV Signal Reception

By Junko Yoshida, EE Times

6-Apr-00

After months of divisive arguments over the need to add an alternative modulation scheme to the US digital TV standard, the broadcasters, chip vendors and consumer electronics companies who have debated the issue came together last Friday (March 31, 2000) to discuss the problem some of them see with terrestrial DTV signal reception.Over 100 people attended the first meeting of a new task force of the Advanced Television Systems Committee (ATSC), formed to revisit DTV standards issues. Participants included many broadcasters and non-ATSC members. While one attendee described the meeting as ""more of a therapy session than anything else,"" giving attendees a chance to vent, Mark Richer, ATSC's Executive Director, said that the meeting was ""truly very positive."" According to Richer, the ATSC task force will focus its work on three areas: a study of current applications and requirements from broadcasters' perspectives, an assessment of the vestigial sideband (8-VSB) modulation scheme chosen by ATSC as the standard for terrestrial DTV, and the development of a common methodology for field testing. At a time when a growing number of broadcasters are showing interest in new businesses such as datacasting and mobile data services, ""We need to know what broadcasters plan to do with their DTV spectrum, other than delivering TV services,"" said one industry source. ""We'd like broadcasters to clarify what their businesses are, and what functions are required for such services."" Standard StudyA subgroup will look into the performance of 8-VSB modulation ""to determine what if anything needs to be done,"" Richer said. Coming up with a consistent testing methodology appears to be one of the most important objectives of the task force. With a common methodology, it is expected that scientists and engineers could finally compare apples to apples when interpreting 8-VSB field test results. Although it is not yet a part of the formal agenda, the ATSC task force may also consider setting a DTV receiver standard. If that happens, it will be a radical step for the ATSC, which has been designed to establish a standard only for broadcasting. The standard for a DTV receiver could also be extremely useful, since it would allow many in the industry - chip makers and system vendors alike - to establish what the target performance of their products should be. As the task force involves more broadcasters in its activities, ""It seems prudent and reasonable to set up a standard for receiver requirements,"" said Robert Stokes, Director for Operations of DTV at Motorola Inc. The DTV industry has been split over whether the US DTV system based on the vestigial sideband has DTV signal reception problems today. Some broadcasters have clashed with chip companies and DTV receiver manufacturers over how to interpret varying assessments, with differing opinions on remedies for perceived problems. Hoping the task force can break the logjam in the DTV market, one industry source who spoke on the condition of anonymity said that this new initiative will finally ""get the issue out in the open"" and hopefully find solutions to technical problems, ""if there are any."" Some broadcasters have claimed that problems inherent in 8-VSB are so serious and basic that the ATSC standard should allow another modulation scheme - coded orthogonal frequency division multiplexing (COFDM), if necessary. Chip vendors, having launched a newer generation of 8-VSB demodulation chips last fall, now say that system-level designs need to be improved before their chips can perform to their full potential. Both Sarnoff Corp. and Motorola, for example, acknowledged that they are working together to tweak the RF front-end of their systems, and are making improvements in software running on MCT2000, a jointly developed DSP for 8-VSB demodulation. Neither company believes, however, that 8-VSB has a fatal flaw. To get better DTV signal reception, ""you need small incremental improvements on all areas including component selection, value selection, circuitry routes on a board and cleaner signals coming out of a tuner,"" said Motorola's Stokes. Most DTV receiver manufacturers, meanwhile, have kept mum on DTV signal reception issues. In general, they are adamantly opposed to any notion of introducing changes to the DTV standard, or to allowing the COFDM option. For most big consumer electronics companies, which have already invested millions of dollars in the development of digital HDTV receivers, it is simply ""too late to turn back,"" according to some industry observers. Pointed ComparisonsA summary of the problems is evident when comparing terrestrial DTV service in the United States with the OnDigital terrestrial DTV service of the United Kingdom, according to Gerry Kaufhold, DTV Analyst at Cahners In-Stat Group (Scottsdale, Arizona). ""Nobody wants to make a complete receiver"" for the US market, Kaufhold said. In the UK, OnDigital engineers test and approve each and every OnDigital receiver system - from antenna to tuner to demodulation to microprocessor software, said Kaufhold. And when a consumer purchases an OnDigital system, an installation technician typically brings the equipment and installs it using instructions from the OnDigital service, he said. ""However, in the United States, the broadcasters don't talk to the consumer electronics companies who don't talk to the tuner companies who don't talk to the antenna companies,"" Kaufhold said. ""It's a laisse faire mess.""