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
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
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
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.