VSB Digital Television Technology Outshines CDFDM In Laboratory Evaluation
Three years after FCC adoption, the digital television (DTV) transmission system called VSB continues to gain momentum, with more than 60 percent of U.S. households now in range of DTV signals. That momentum for the VSB standard also was exemplified by literally dozens of next-generation DTV receivers shown at the International Consumer Electronics Show in January 2000 by Thomson, Philips, Sony, Zenith and others - further weakening a challenge from Sinclair Broadcasting. In an apparent attempt to delay its investments in making the transition to digital broadcasting, Sinclair has petitioned the FCC to consider giving broadcasters the option of using the European transmission system, called COFDM. The Consumer Electronics Association and its members have countered, urging the FCC to reject this 11th-hour Sinclair delay tactic. For its part, the developer of the VSB (vestigial sideband) system, Zenith Electronics Corporation, showcased the strength of the standard at the CES with a compelling comparison of VSB and COFDM receivers. Zenith turned a private suite in the Las Vegas Hilton into a working laboratory, complete with racks of equipment and multiple HDTV receivers and displays. There, broadcasters, government officials, chip makers and fellow equipment manufacturers saw first-hand the superiority of the U.S. VSB standard over COFDM and performance improvements found in current- and next-generation VSB receivers. Underscoring VSB's superior DTV signal coverage and rejection of ""impulsive noise"" were a series of evaluations in which multiple ghosts and other real-world impairments were introduced into VSB and COFDM modulated signals and, as a reference, into NTSC signals. Results show, for example, that in Baltimore, Maryland (where Sinclair conducted DTV demonstrations last summer), COFDM would reduce signal coverage area by 12 percent compared with VSB, according to Joseph Flaherty, CBS Senior Vice President. That represents more than 700,000 television households, which significantly dwarfs the small number potentially affected viewers relying on indoor antenna reception in certain urban settings. Richard Lewis, Zenith Senior Vice President, Technology and Research, explained that results also show that impulsive noise - electrical interference caused by hair dryers, vacuum cleaners, automobile ignitions, electrical power lines, etc. - severely limits COFDM's usefulness, particularly on VHF channels. User experience in Europe has exposed this problem, he said. In addition, using some of the same equipment and testing procedures that the FCC Advisory Committee on Advanced Television Service used to evaluate DTV systems, Zenith showed how VSB receivers cancel multiple ghosts - comparing today's superior performance to the poorly performing receivers hand-picked by Sinclair for its attempt in Baltimore to discredit the ATSC DTV standard. ""8-VSB continues to outperform COFDM,"" Lewis concluded, referring to VSB's superior coverage area and impulsive noise performance. ""Plus, new data show that current and next-generation VSB receivers offer comparable ghost performance to COFDM in 'concrete canyon' urban environments and indoor reception, and superior VSB ghost rejection for the majority of viewers."" Currently, Zenith is conducting an improved demonstration, utilizing a third generation Zenith STB, performing multipath tests in Washington D.C. for interested parties, including the NAB, MSTV, Office of Technology assessment at the FCC.