Jan. 12, 2000 (INSIDE DIGITAL TV, Vol. 3, No. 1 via COMTEX) -- DVB, the European digital standards body, has finally intervened in the US row over the respective merits of 8-VSB (the modulation scheme used in the US ATSC digital TV standard) and COFDM (the modulation scheme used in the European DVB-T standard). The move coincides with new evidence suggesting that the second-generation VSB chipsets designed to address ATSC reception issues are failing to cure the problem.
In a letter dated December 16, Peter MacAvock, head of the DVB Project Office, wrote to the US regulator charged with resolving the dispute, the FCC, enclosing a copy of a confidential report to the Mexican regulatory authority, the SCT, which is currently reviewing which of the two standards to adopt.
The DVB's action - taken with the permission of the Mexican authorities - was spurred by the revelation of the contents of the ATSC's own report to the SCT, which charged - among other things - that the Sinclair Broadcasting Group's comparative tests of 8-VSB and COFDM (Inside Digital TV Vol.2 No.21) were "badly biased" and constituted an "unsound and unfair attempt to discredit the ATSC standard." The ATSC argued that all that Sinclair had demonstrated was that "many of the first generation DTV receivers do not perform well enough in the presence of severe multipath impairments. But this is a problem with some receiver implementations, not with the VSB transmission system (ATSC's italics)." The ATSC noted that new chips would soon be available which would all but cure the multipath interference problems, which are caused by multiple signals arriving at an antenna at different times due to obstacles such as buildings or automobiles.
The ATSC's report - which also claims that "DVB receivers would cost about $80 more at retail than ATSC receivers" - was subsequently copied to the FCC as part of its campaign to oppose Sinclair's petition to the FCC, which requests that COFDM be made available as an optional modulation system for US digital TV broadcasters.
The DVB's Mexican submission notes that "recent statements from the ATSC have shown that they do not disagree with the Sinclair findings but cite the fact that the problem with reception was due to the use of early receivers. This has led to many hyped press statements that a new range of miracle chips will be available soon. Even if this is the case and these chips do improve performance the projected cost of the silicon quoted by the manufacturers will make the receivers more expensive and will also completely eradicate the myth that ATSC receivers will be cheaper than those receiving COFDM."
What DVB did not know at the time it wrote its submission to the Mexican authorities was how the new range of VSB chips - from Motorola and NxtWave - would perform in practice. In August last year, Motorola had boasted that its "new digital receiver technology [...] solves a potentially serious reception problem in digital and high-definition (DTV/HDTV) broadcasts that use the Advanced Television Systems Committee (ATSC) transmission standard [...]. Addressing this issue, Motorola, in collaboration with TV pioneer Sarnoff Corporation, has created a proven, revolutionary digital signal processing architecture [...] that provides excellent signal reception, even under difficult ghost signal conditions found often in urban areas."
But now, in a further twist to the affair, Motorola has posted on one of its Web sites data from field tests of the new MCT2100 demodulator chip which show these claims to be untrue and that - far from supporting the ATSC case - demonstrate that DVB was entirely right to be sceptical about the efficacy of the new technology.
The most damning evidence comes from the field test report carried out by Motorola and Sarnoff in Philadelphia, and written up by their own engineers. This admits "the field test results were mixed" and showed that "multipath in the real world is much more complicated than what we are able to generate in the lab." It goes on to say that "it was revealing, though unfortunate, to find that in many sites (or antenna positions at a site), the limiting factor preventing reception was multipath [interference], not received signal power." On another critical point, indoor reception, the engineers noted that "none of the locations where such reception was possible [...] had more than 105 degrees of receivable positioning". This, they concluded, "has negative implications for channel surfing in cities in which the TV transmitter towers are not co-located for all stations."
In the most recently-published field test report - for San Francisco - Motorola engineers found that, across 15 different test sites, there were only two where the new receivers were able to obtain fault-free reception >from all five networks transmitting digital TV signals.
On January 4, Sinclair released results from its own trials of the newest digital TV receivers in Baltimore and Washington, concluding that "the latest generation of digital television (DTV) receivers failed to provide more than marginal improvement over earlier receivers, and still failed to provide acceptable over-the-air reception using simple consumer antennas."
The FCC, for its part, has not yet determined whether to open up the issues raised by Sinclair to public consultation, despite Sinclair having submitted its petition on October 8, three months ago. The latest test results will no doubt increase pressure on the regulator to put the petition up for debate rather than simply rejecting it out of hand.
