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ATSC Transmission Standard Flawed, says Sinclair Broadcasting

Unheard by the general public, a debate has been raging in engineering circles about the Advanced Television Standards Committee's transmission protocol for high-definition TV. Mandated by the Federal Communications Commission, the standard, known as 8-VSB (trellis-coded 8-level vestigial sideband), has come under fire from several directions, most notably from Sinclair Broadcasting, which has called for an overhaul of the standard after a series of DTV reception tests in the Philadelphia area.

The tests looked for reliable over-the-air reception of digital video signals within a 20-mile radius of a Philadelphia broadcast tower. The results were discouraging, company engineers say. "In nine out of nine locations, we got no reception—just the blue screen of death," said Nat Ostroff, Sinclair's VP for new technology. DTV receivers that have difficulty locking on to a digital signal do not display snowy pictures like their analog counterparts; they simply put up a solid blue screen if the signal is below a certain threshold.

Sinclair's tests revealed that the 8-VSB scheme is not nearly as robust or reliable as one favored by European and Asian broadcasters, known as COFDM (coded orthogonal frequency division multiplexing). According to Sinclair, the 8-VSB technique is prone to interference from trees, hills, buildings, bridges, and other obstacles. Sinclair, with the cooperation of what Business Week calls "a few hundred other TV stations," has petitioned the FCC to reconsider the transmission standard. Consumer electronics makers are understandably upset about any further delays in the rollout of digital television, which has been hampered by slow acceptance by consumers. A standards change at this point would be a marketing disaster, many of them feel, despite the fact that fewer than 50,000 US households have DTV receivers at present, out of a total of more than 97 million with "legacy" TV.

One year after the debut of DTV, broadcasters are ahead of schedule with installing DTV equipment and rolling out DTV programming. But only 30 of 1600 American TV stations have arranged to get their digital signals carried over cable, which delivers TV signals to two-thirds of American households. The remainder—those citizens in the "footprints" of the 1570 stations that will put their DTV signals on the air—must rely on rabbit ears or rooftop antenna systems. Some engineers and executives have questioned whether DTV is suitable for terrestrial broadcasting at all, citing cable providers and satellite services as better adapted for the new technology. Limiting DTV to only those carriers would effectively cut out consumers without either cable or satellite, a situation the FCC would never tolerate. The changeover to DTV is also being slowed by legal maneuverings. Copyright issues for the new format haven't been ironed out.

Sinclair Broadcasting insists that the rapid acceptance of DTV in Britain is due to the robustness of the COFDM scheme. The FCC has taken Sinclair's field tests under consideration. Will the ATSC standard be modified before the DTV format attains critical momentum? No decision is expected soon.

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