8-VSB: Where do we go from here?

NAB, MSTV back the existing standard but demand quick improvement

While questions remain about the state of the technology, the broadcasting industry last week voted overwhelmingly to back the 8-VSB digital modulation standard over the competing COFDM system.

Of the 32 broadcasters assembled in Carlsbad, Calif., for the National Association of Broadcasters winter board meeting and the Association of Maximum Service Television's vote on the transmission standard, 29 supported 8-VSB. Sinclair Broadcast Group, Pappas Telecasting (both of which had representatives on site but are not members of either group) and Paxson Communications were the only broadcasters who were against a joint NAB-MSTV resolution supporting 8-VSB.

In adopting that resolution, the association boards said: "We conclude that there is insufficient evidence to add COFDM 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."

Now the NAB engineering staff must develop a plan to improve 8-VSB. That plan will include determining how much money the industry effort will require. Board members say they expect the NAB staff to come back to them in mid-March.

MSTV has already raised about $1.8 million from broadcasters for comparison testing of COFDM and 8-VSB (Phase I of the VSB/COFDM project) and further investigation of implementing COFDM in the U.S. market (Phase II). About a third of that money has been spent so far on the comparison testing, says MSTV Senior Vice President Victor Tawil, and the original Phase II plan was scrapped after the MSTV-NAB vote. Whether that money will be used to explore enhancement for 8-VSB, the new goal of MSTV and NAB, is unclear.

"The resolution does not translate to that money," says Tawil, who expects new funding to be required for 8-VSB development.

The need to "enhance" the 8-VSB standard to support portable, and perhaps even mobile, DTV reception was recognized by the Advanced Television Systems Committee last summer, when it announced a proceeding to improve the 8-VSB standard. Work on new VSB demodulation technology is already under way at chip makers such as Zenith, Philips and NxtWave, and the ATSC will release a formal request-for-proposal (RFP) in February.

"We're going to cast a wide net looking for proposals to add new functionality to the standard as well as improved performance," says ATSC Executive Director Mark Richer.

Zenith has two sets of VSB enhancements "fairly along in development," says Zenith Senior Vice President Richard Lewis. One called R-VSB, for robust VSB, is a "multi-rate" system that would break the 19.4 Mb/s DTV stream into two parts, devoting about 12 Mb/s for normal DTV applications such as HDTV broadcasts and the remaining 7 Mb/s for applications requiring more robust reception, such as datacasting. R-VSB would improve the receivability of that portion of the DTV signal but reduce the usable data rate; for example, 7 Mb/s modulated in rugged mode might net 3.5 Mb/s of throughput. Using R-VSB, Lewis stresses, would not hamper the receivability of the less rugged portion of the signal. Zenith expects to demonstrate prototype hardware using R-VSB by the NAB convention.

Another schema being worked on by Zenith is VSB-M, or VSB mobile, that would receive signals on-the-go but would only achieve about 4 Mb/s of throughput. Zenith expects to create a VSB-M prototype in the first quarter, but doesn't plan public demonstrations.

Richer thinks the MSTV/NAB technical report and subsequent vote should put the VSB/COFDM debate to rest.

"There may be one or two organizations out there pushing for an alternative, but I think the industry is pretty united now," he says.

Sinclair might disagree. The station group still believes COFDM is the better standard, and ran last-minute tests Jan. 14 to prove its point.

Sinclair alleges the MSTV/NAB testing of COFDM was prejudiced because the European DTV receiver used was not optimized for the U.S. market. Sinclair says the COFDM receiver, which had been modified to receive the U.S.'6 MHz DTV channels, didn't have proper "front-end filter" protection to deal with signal overload from analog TV, cell phones and FM radio signals in the testing environment.

According to Sinclair, that's why the COFDM signals actually performed worse when received by a 30-foot antenna than when received by a 6-foot antenna. VSB reception, on the other hand, improved dramatically when the 30-foot antenna was used.

While MSTV sources indicate Sinclair was intimately involved with the testing all along and has no reason to complain, Sinclair executives say they weren't made aware of the "COFDM anomaly" until late November, when the MSTV-NAB report was already being drafted.

"The results of the field testing for both receivers proved, beyond a reasonable doubt, that the COFDM receivers and, consequently the COFDM data taken from the tests are not representative of the correct results," said Sinclair VP of New Technology Nat Ostroff in a statement. "In short, the COFDM results are simply wrong!"

Sinclair's complaints ultimately had little effect on the vote, and both the NAB and MSTV boards adopted the resolution.

As for the Big Four networks, NAB board members ABC and CBS agreed to back 8-VSB, even though last April engineers at Disney-owned ABC were warning the industry that COFDM might work better. NBC and Fox didn't attend the meeting because neither network belongs to either association, but attending board members say Fox is aboard. An NBC source confirmed NBC's approval.