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Moderating the American
DTV Modulation War
by Ken Freed.
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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." end
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Broadband Week
First Published in Broadband Week, February 2001.
Revised.
(c) 2000 by Judah Ken Freed


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