Letter from Joe Flaherty to ATSC VSB Performance Ad Hoc Group on 8-VSB vs. COFDM Testing

This letter from Joe Flaherty to the ATSC committee has been circulated about in E-mail forums. Some mock it saying it is so unrealistic because so few decoders in the marketplace makes the movement a failure more than an "inexorable march toward an all-digital television system in America!"

To:  Frank Eory, Chairman ATSC VSB Performance Ad Hoc Group
From:  J. A. Flaherty, Senior Vice President Technology, CBS Television
Subject: “Draft Report of the VSB Performance Ad Hoc Group to the ATSC Task Force on RF System Performance”

Letter From Joe Flaherty
CBS, Inc.

As you know, the rapid improvements in ATSC 8-VSB receivers over the last few months have made most significant advances in the overall performance of the ATSC 8-VSB digital transmission system. These improvements have been tested and documented by the MSTV/NAB COFDM/8-VSB Project Group with similar tests well along by the CRC in Canada and 8-VSB tests conducted by the FCC. In fact, one 8-VSB receiver is working at -1db ghosts, up from -3db. Many of the chip manufacturers are approaching 0 db. ghosts.

Since the MSTV/NAB tests are complete and the report will be finished by year-end, the results of these tests combined with the CRC tests in Canada represent state-of-the-art objective American tests. The “Draft Report of the VSB Performance Ad Hoc Group to the ATSC Task Force on RF System Performance” cannot be considered complete and prepared for transmission to the ATSC Task Force on RF System Performance without the incorporation of these American test results.

While the foreign test data may be also useful, it is over a year old, and at the speed with which 8-VSB improvements have been, and are being, made; much of that foreign data is ancient history. In short, it is absolutely essential to include the MSTV/NAB test data in the report. Without it, the ATSC Task Force, the ATSC Executive Committee, and many outside organizations will challenge the thoroughness and accuracy of the report.

The care with which the ATSC report has been assembled so far argues strongly for incorporating the American test results, as this will only involve six to eight weeks of delay – a small price to pay for timeliness and accuracy.

The American COFDM/8-VSB test results could well result in major changes in the Draft Report, especially in its “Executive Summary, "Conclusions", and "Recommendations”.

Specifically, the final paragraph in the Draft 4.2 Executive Summary in lines 20 through 26 must be deleted pending the results of the American COFDM/8-VSB test results. Those results will determine what, if any, recommendation is required on the need for further investigations of alternative DTV transmission systems in the U.S. environment.

Similarly, the Draft 4.2, Section 9 “Conclusions” in paragraphs 9.3 and 9.4 note, among other things, that: “…the field test data available to the group, which is largely based on the Grand alliance receiver implementation, …”. These data are, of course, wholly obsolete. Newer versions of 8-VSB receiver designs were utilized throughout the MSTV/NAB tests as well as in the FCC tests. These new data will likely have a profound effect on the conclusions reported in the Draft Report 4.2. Both of these paragraphs, lines 1283 through 1322 and lines 1324 through 1347, need to be deleted as they will need to be largely rewritten based on the modern American test results from the CRC and the MSTV/NAB tests.

The Draft 4.2, Section 10 “Recommendations to the Task Force on RF System Performance” in paragraph 10.5 takes notes in lines 1448 to 1450 that “…comparative tests of DVB-T and ATSC are being currently being conducted in the U.S.” As noted above, these U.S. comparative tests are completed and the report is being finished in the next 60 days. Thus, as reported in lines 1451 to 1454, the need for the group to “recommend ATSC conduct a performance assessment of the two COFDM systems and their applicability or lack thereof for U.S. DTV” is clearly premature. These four lines must be deleted until the MSTV/NAB comparative test results have been evaluated and incorporated into the Draft report. Then, and only then, could the Ad Hoc Group sensibly conclude that: "…there is an industry need for a balanced review of these alternative modulation systems and how they compare with 8-VSB."

The Draft 4.2 of the report cannot be sensibly released to the ATSC Task Force and beyond until the modern American test data is included and the report updated to reflect the present state-of-the-art! Lacking the modern up-to-the-minute American test data, the good work so far accomplished by the ATSC will go for naught!

It should also be noted that the recommendations made in paragraphs 10-2, 10-3, and 10-4 will require significant time to complete, and Tempus fugit! There may be little opportunity to pursue such recommendations with the digital rollout well underway and accelerating.

As put by Hippocrates:

“Time is that wherein there is opportunity, and opportunity is that wherein there is little time.”

The DTV/HDTV rollout cannot be slowed or stopped in its inexorable march toward an all-digital television system in America!