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Ken Davies: ATSC Transmission Model Must Be Redefined Before 8VSB vs. COFDM Testing Can Proceed

Ken Davies · 1999

Mentioned: Ken Davies, Bob Graves

Summary

Broadcast engineer Ken Davies argues that the fundamental flaw in the ATSC DTV rollout is an outdated transmission model inherited from the NTSC era, not the technical standards themselves. He calls for consensus on a new service model emphasizing portable, plug-and-play reception before further 8VSB versus COFDM testing debates can be resolved.

Source documentcirca 1999preserved as-is

"The Sinclair petition has certainly focussed attention on some of the key aspects of the service model"

Ken Davies

 

    The information from NxtWave and from the Sinclair petition have generated a great deal of mail and perhaps I can now add my own views to the string before things become even more politicized (witness Bob Graves famous letter and the latest CEA salvo of smoke!!)

    I think many would agree that the real problem with ATSC and the preceding ACATS activities is simply that the transmission model used, while reasonable at the time, did not take account of the future adequately, frequently a problem when politics enter into technical decision making. The technical work done was, however, excellent and the conclusions supportable in the context of the model used. I have the greatest admiration and respect for those involved. It is clear however that this model is today overwhelmed by new technologies in wireless delivery, enhanced expectations of users and by a marketplace that is totally changed. It is little wonder that the model and the standards it spawned are under attack, though much of the ATSC standard, I would point out, has stood the test and remains highly acceptable to all.

    This basic transmission model, with its concentration on spreading the signal thinly over square miles of the landscape,

    The real problem with ATSC and the preceding ACATS activities is simply that the transmission model used, while reasonable at the time, did not take account of the future adequately, frequently a problem when politics enter into technical decision making.
    taking insufficient account of the city centers and leaving the viewer to figure out how to receive it, is no longer viable. The model of today is strongly tilted towards delivering a highly receivable signal to as many people as possible, with an emphasis on highly reliable plug-and-play, cordless receiving devices, many effectively portable and others, perhaps, mobile. The standard for plug-and-play performance is established by competing media and the DTV system must do better, or fail in the marketplace. This concept was not unknown when 8VSB was selected, many even then could see the requirement was far more evolutionary than simple replacement of NTSC. I can recall spending a large amount of effort, energy and money with others in testing and in demonstrating the eminent suitability of a COFDM system for this enlightened model of TV broadcasting to a number of groups. In the five years the technology has matured, the market has changed dramatically and continues to change, making a forward-looking choice even more desirable. Even the "enlightened" model now needs some updating.

    There is thus a priority that must be dealt with before a response can be made to the many calls for further testing that are heard on all sides. Simply put, which model is to be the basis for testing? A repeat of the previous tests, derived from the 1950's era NTSC model, considering DTV as an NTSC replacement or a new model, using advanced wireless service concepts to maximize reliable, ubiquitous receivability on simple receivers to the largest number of users, fixed, portable and mobile? If the service model cannot be agreed, there is little chance of reaching the right decisions, or even of conducting useful testing. In that case the discussions of the relative merits of VSB and COFDM transmission will continue to fill my in-box every day, each being right in their own chosen context.

    The Sinclair petition has certainly focussed attention on some of the key aspects of the service model. What of the others? Is it not time to begin a discussion thread that could lead to a convergence on this key part of the search for a resolution? What do we think are the essential characteristics of the transmission model? With that in hand, progress can be made and DTV could evolve into a useful and viable service to the intended audience.

    I await comments with interest!

    Regards,

    Ken.Davies
    [email protected]

 

Copyright 1999

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