Officially, Canada has committed itself to supporting the ATSC/8-VSB standard for digital television. But this hasn't stopped a consortium of Canadian private TV broadcasters-CTV, Global and CHUM television-from obtaining government permission to test COFDM against 8-VSB in Toronto.
The 18-month experimental permit, which Industry Canada granted at the beginning of the year, was inspired by Canadian broadcasters' doubts about 8-VSB's performance. In particular, the consortium wants to know whether "the coverage objectives that broadcasters have for DTV can be effectively fully mapped by 8-VSB," says Wayne Stacey, an Ottawa-based engineering consultant and vice chair of the CDTV Technical Working Group, the organization of private and public broadcasters in charge of Canada's DTV rollout.
It's safe to say that the Canadians-whose actual DTV rollout has so far been restricted to a single ATSC/8-VSB test transmitter south of Ottawa-are skeptical about 8-VSB's performance. So skeptical, in fact, that "there is some wish on the part of broadcasters to look at alternative methods," Stacey says. "COFDM is the most obvious, just because it happens to be the modulation system that's used in the European DTV system."
Actually, the real reason Canadian broadcasters are interested in COFDM is money. If they're going to switch to DTV, they want to make a profit. Unfortunately, 8-VSB, with its indoor-reception problems and inability to support mobile reception, doesn't quite fit the bill.
In contrast, COFDM, which Canada is already using for its L-band (1.452-1.492 GHz) digital radio system, is able to do those jobs, says Terry Harvey, a member of Ryerson Polytechnic University's broadcast engineering systems faculty in Toronto and a consulting engineer with CDTV. As a result, COFDM is a natural choice for Canadian broadcasters, who are running the Toronto trials to gauge DTV's commercial potential. Says Harvey, "COFDM modulation lends itself to a variety of delivery methods that will support new and interesting business plans for the broadcaster, which 8-VSB will not be able to do."
The Toronto DTV trials will be based at the city's CN Tower, which is already home to Toronto's radio and analog-TV transmitters. The signals themselves, which will comprise clips from a video server, will be transmitted through a 200-watt transmitter. These will initially be fed into Citytv's standby antenna on Ch. 66. Later, in order to get more-accurate coverage data, the signals will be diplexed into Citytv's main antenna on Ch. 57.
Ironically, even if COFDM does outshine 8-VSB in Toronto, "it's probably quite unlikely that Canada would adopt a different standard than the United States," Stacey says. The reason is pragmatism: Canadians live and die by U.S. TV broadcasts, and their production industry relies on selling into the American market.
"On the other hand," he adds, "by doing this work, we may generate information that would be useful in a North American-wide context, to see whether a change might be appropriate." This means that Canada's research might be enough to help win U.S. acceptance for COFDM, which would encourage Canadian broadcasters to deploy it as well.
Although they're being ostensibly staged for Canadian broadcasters, the Toronto COFDM/8-VSB tests are really aimed at the U.S. broadcasting industry. What remains to be seen is whether the results actually matter to U.S. broadcasters, many of whom have already invested heavily in 8-VSB.