McAdams On: The Mobile Legacy of 8VSB vs. COFDM

10/29/2010 3:10:26 PM
It’s difficult to sit through a technical session on the mobile DTV standard and not sense the elephant. It’s virtually impossible to not wonder where mobile DTV would be today if the fixed standard were different.

The acrimony over establishing that fixed standard still resonates such that it’s risky to revisit the schism. And yet with the emergence of mobile DTV, the old duel seems now a Kafkaesque irony.


The year was 1998. I was a relatively new trade hack having discovered that local print journalism paid about the same as planting trees. I stepped right in the middle of the great DTV transmission schism: eight-level, trellis-coded vestigial sideband versus coded orthogonal frequency-division multiplexing. Or more mercifully, 8VSB vs. COFDM.


8VSB was notoriously vulnerable to multipath distortion. It was concentrated and bounced off buildings like a Super Ball. COFDM was a bit more dispersed and could wend around obstacles. Clearly “Super Ball” and “wend” were not part of the technical diagnostics related to me over hundreds of hours of conversations with engineers bent on making my head explode. The over-simplification is my likewise payback.


The characteristics of COFDM made it more suitable for mobile DTV, but the broadcast industry as a whole wasn’t thinking mobile DTV back then. It was thinking replication of analog signals. Sinclair’s David Smith was thinking about mobile DTV, however. Sinclair had auto dealerships as well as TV stations.


Smith told me during a phone interview in ’98 that Sinclair wanted COFDM to do mobile DTV. No clutch of shrinking violets, they, the Sinclair team set about getting COFDM into the fixed DTV transmission standard.


By then, the industry was already moving toward 8VSB, which was developed by a subsidiary of Korean TV set maker, LG. TV sets had a lot to do with the efficacy of a transmission standard. They had to decode it. 8VSB was said to be a bit better in that regard, but the fact that LG stood to make millions on licensing fees tainted the well.


Fur flew. Accusations were hurled. Tests were conducted, questioned, dismissed and/or affirmed. 8VSB won. That’s the way it was and still is, so a new standard had to be developed for mobile DTV. Along with it, new transmitter components and new receivers.


Those receivers are just now coming to market. TV stations are just now coming online with mobile DTV, which uses some of their 19.4 Mpbs payload. Next year is supposed to be the watershed year for Mobile DTV with a capital “M,” even though the industry now has three disparate groups working on business and marketing plans. The potential for dissent is historic.


To boot, regulators-cum-private equity investors are intent on excising 40 percent of the spectrum now used for broadcast TV. I understand how touchy this industry is about Mobile DTV skepticism, and how expressing it is considered by some nearly blasphemous. But seriously. How many elephants can one fit into a room?


Had COFDM been adopted, mobile DTV may have grown organically. No payload encroachment or facilities modifications necessary. The only receiver differentiation would have been form factor. Broadcasting could have evaded its addiction to retransmission money.


One can’t help but wonder.

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