Moderating
the American
DTV Modulation War
by Ken
Freed.
.
8VSB
beats COFDM in digitalTV reception tests, but American
DTV signal needs 'urgent' upgrade.
After
a U.S. field test capping two years of bitter controversy
with broadcast fortunes at stake, America's digital TV
signal modulation standard is "in" and Europe's DTV
modulation standard is "out."
U.S. broadcasters
have affirmed their initial preference for "8VSB" signal
modulation, the digital terrestrial TV transmission
standard adopted by the FCC, instead of its European
rival, "COFDM."
Yet the victor
barely passed muster. The high-profile study called for
"urgent" improvements in VSB technology.
Under U.S. law, all
commercial broadcasters must air a digital signal by May
1, 2002, and non-commercial broadcasters must be digital
a year later. All analog U.S. broadcasts must end in
2006.
Conducted jointly
by the National Association of Broadcasters (NAB) and the
Association for Maximum Service Television (MSTV), the
tests compared reception of eight amplitude-level
vestigial side band (8VSB) signals with the reception of
signals modulated by coded orthogonal frequency-division
multiplexing (COFDM).
While the technical
debate may never be resolved ultimately, the political
dispute was settled at a combined January NAB-MSTV winter
board meeting in Carlsbad, Calif. Among the 32
broadcasters represented, 29 votes favored a joint
resolution supporting 8-VSB.
The Federal
Communications Commission is taking the joint resolution
as an affirmation of its policies. The FCC can stick with
its initial choice and save face, in other words, but
digital TV reception problems must be fixed before
digital TV in America can succeed.
The
Fight
The three holdouts
against VSB in Carlsbad were Paxson Communications,
Pappas Telecasting, and Sinclair Broadcasting.
The most ardent
U.S. backer of COFDM, Sinclair sparked the controversy
two years ago. Arguing that 8VSB reception suffered from
urban "multipath" echoes and bandwidth interference along
with portable and mobile TV reception problems, Sinclair
in 1999 petitioned the FCC to add COFDM to the Advanced
Television Systems Committee (ATSC) standard adopted by
the FCC. The goal was not to replace 8VSB, but to add a
COFDM option where the local broadcast conditions
warrant.
Seeing no
justification to defer 8VSB deployment, given that COFDM
did not seem significantly better in its own comparison
tests earlier, the FCC rejected Sinclair's 1999 petition.
But the debate did
not stop there.
NBC, ABC and other
U.S. network broadcasters conducted their own digital TV
reception tests, then told the FCC in summer 2000 that
they also distrusted 8VSB.
Network defections
from 8VSB sparked a heated Congressional hearing in July
where U.S. legislators warned broadcasters that any delay
launching digital TV and returning the analog spectrum
(for auctioning) by 2006 would be the "deal breaker" for
Congress.
The challenge to
8VSB, in other words, was endangering the "loan" to
broadcasters of free spectrum for digital TV. Sinclair
and others advocating COFDM were seen as threatening the
sacred cow.
Testing,
Testing
Facing a crisis,
NAB and MSTV agreed to conduct "scientifically rigorous"
field tests to settle the question once and for all,
creating the joint "VSB/COFDM Project" to perform the
research.
Responding to an
American request for testing equipment, four European
COFDM vendors came forward with offers to modify their
DVB-T COFDM receivers from Europe's 8 MHz channels to
America's 6 MHz channels. The VSB/COFDM Project team
selected the test and measurement receiver from Broadcast
Technology Ltd in the UK.
The COFDM receiver
was tested side-by-side with an 8VSB receiver at eight
sites in Cleveland, Baltimore and Washington, DC.
Reception tests were conducted outdoors with standard TV
antennas at six feet and 30 feet, then indoors without a
rooftop antenna.
Outdoor reception
for 8VSB and COFDM were comparable, the study reported,
yet 8VSB and COFDM also were about the same, which meant
the COFDM receiver did not perform indoors as well as
advocates predicted.
Regardless of COFDM
problems, the big news was that 8VSB's outdoor and indoor
reception was found sorely lacking. COFDM may not be
better than 8VSB, in other words, but 8VSB has big
problems.
"We conclude that
there is insufficient evidence to add COFDM [to
ATSC]," stated the NAB-MSTV joint resolution, "and we
therefore reaffirm our endorsement of the VSB standard.
We also conclude that there is an urgent need for swift
and dramatic improvement in the performance of the
present U.S. digital television system."
MSTV senior VP
Victory Tawil reported the study cost a third of the $1.8
million raised from 30 broadcasters to support the field
tests plus investigations into implementing COFDM if it
was found superior.
Further COFDM study
is now moot, he says, but no decision has been made if or
how the remaining balance of about $1.2 million will be
applied toward the "urgent" 8VSB improvements.
The
Protest
Sinclair
Broadcasting Group is challenging the validity of the
tests by circulating a letter from Broadcast Technology
Ltd saying its DTVM200(T) COFDM receiver was misused.
"It has come to my
attention that my company's product is being blamed for
providing less than optimal performance," wrote BTL
managing director Nicholas Jennings in a January letter.
"The fact is that our product was used in a manner for
which it was not designed nor intended, and the result of
this misguided use has led to misleading results and
incorrect conclusions. ...The integrity and validity of
the data collected using our product in a direct antenna
connected terrestrial receiving environment can be
dismissed as being irrelevant and speculative at
best."
"That's just sour
grapes," said Gary Shapiro, president and CEO of the
Consumer Electronics Association, alleging Sinclair was
behind the letter. "The COFDM issue in America is over,
done, dead, gone."
Shapiro says CE
manufacturers don't care which standard the U.S. adopts.
He dismisses as unimportant the fact CE assembly lines
already manufacture 8VSB receiver sets and have been
waiting to produce more once the COFDM debate was
settled.
"The problem here
is maximum coverage area with minimum signal
interference," said Matt Miller, president and CEO of
NxtWave Communications, which produces 8VSB and COFDM
receiver chipsets. He voiced surprise that COFDM did not
out-perform 8VSB indoors, as expected, but he would not
blame the receiver.
"I can't say enough
about how hard everyone tried to do a balanced and
objective evaluation," said Miller, who participated in
the field tests. "We could find no valid technical reason
to delay the implementation of digital TV for the two or
three years it would take to develop and approve a new
U.S. transmission standard. Ultimately, the decision was
a practical one."
According Bruce
Franca, acting chief of the FCC engineering and
technology office, "Sinclair deserves kudos for pushing
development of 8VSB a few years ahead of where it would
have been otherwise, and for pointing out where 8VSB
still needs to go."
Sinclair's VP for
new technology, Nat Ostroff, said the addition of COFDM
capacity would cost only $20,000 per station, and COFDM
installation would not be difficult for station
operators. Ostroff may seem resigned to losing the
political battle for COFDM, but he is far from done
discussing VSB reception problems.
"If the industry is
going to devote a significant amount of time and
resources to improving 8VSB," Ostroff said, "we welcome
it, and we will contribute whatever we can to make that
effort a success. It's in our own self interest to have a
broadcast standard that works." 
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