Make the most of the ‘20Mb/s pipe’ today, or face uncertainty tomorrow

In the last edition of HD Technology Update, Merrill Weiss urged television broadcasters to begin thinking out of the box about how they offer over-the-air television.

In this edition, HDTU concludes the interview with the NAB2006 Television Engineering Achievement Award winner.

HD Technology Update: ATSC over-the-air transmission of HD is delivering service today that is unsurpassed from the point of view of quality. Is that enough to keep broadcasters competitive, or must they take other steps to win back the audience to over-the-air service?

Merrill Weiss: We need to recognize that the satellite operators and most likely the cable operators are reducing the bit rate of the signal that broadcasters transmit — especially for HD — and that it ultimately reduces the quality of the image that can be displayed in a consumer’s home.

Whether that can be turned into an advantage by broadcasters for attracting people back to over-the-air reception will depend on whether broadcasters are even willing to promote the fact that they do have the best signal. Given that most broadcasters don’t even promote that they have an HD service on the air, it’s hard to see broadcasters promoting that their signal is superior to that of satellite or cable. And a second question is: How many people in the audience will that really matter to?

HDTU: Clearly one of the goals of the ATSC transmission scheme was a robust over-the-air method to deliver high definition television. Were the smallest of screens — i.e. LCD cell phone displays — ever considered as ATSC standards were being defined? Is there room in the ATSC transmission scheme to accommodate broadcast service to handsets as there is with DVB-H? I know one of your primary focuses has been DTV distributed transmission. Could that technology be useful in broadcasting to handsets (cell phones)?

MW: In the earliest stages of the development of what is now the ATSC system, the decision was made that the service to be provided was over-the-air transmission to fixed locations based on assumptions that people would be using an outdoor antenna at 30ft — on the rooftop. The objectives that were set did not include the transmission to portable or mobile receivers.

As other systems developed, the question has been raised in the ATSC context as to whether or not advancements or extensions should be targeted toward enabling portable and mobile reception. In fact, there have been some enhancements already adopted by the ATSC that help with reception in weaker signal areas.

Additionally, it recently has been proposed that they carry the potential further, and among the possible targets are portable and mobile receivers. But you have to recognize that, when you configure the signal to address portable and mobile reception, you are making a trade-off in the bit capacity of the signal in order to achieve the improvement in robustness required for non-stationary reception. And that tradeoff can be 2-to-1 or 4-to-1, so you get only half or a quarter of the bit capacity in return for more robust reception.

Clearly, if you were going to move in that direction, you would need to use more advanced coding to somewhat or fully make up for the loss of bit rate you would suffer to achieve the higher robustness. Even with that more efficient coding, you still might not have enough capacity left to do HD transmission if you were trying to provide service to cell phones.

If you did want to provide mobile and portable service, another factor that comes into play is that you would want to have multiple transmitters to improve the robustness of the system even if you were using lower bit capacity. When moving a receiver around, there will be places where the signal is cut off abruptly. So having signals illuminating those areas from a number of directions will help to mitigate those problems and to resolve that issue. Besides that, putting transmitters closer to receivers reduces the fading of the signals that will be received by the moving receivers.

It is important to recognize that, unlike a cell phone system, where each transmitter at each cell site is on a different frequency from the neighboring transmitter, and each cell uses a number of channels to cover the same sector for the same cell, if you are talking about a broadcast transmitter, it has to have exactly the same information on the same frequency from each cell. So you have to build technology into the receiver to eliminate echoes and extract the data from those signals.

Some of the other transmission systems, such as DVB-T, have been designed specifically to enable mobile and portable reception. It’s not entirely clear whether the ATSC system can be expanded to do that. It depends very much on what receivers have in their front ends for echo mitigation.

There is a technology that’s been brought to the ATSC recently that is being evaluated and might have some potential. It’s too early in the process to know how far it can be pushed and what can be achieved.

HDTU: Look down the road 25 years. What do you see in terms of the digital transmission capabilities of over-the-air television stations?

MW: Twenty-five years is very long time. It is hard to know what broadcasting itself will be like in 25 years. What can be envisioned is that the utility of a pipe into virtually every house in the country that can provide nearly 20Mb/s of data from a number of parallel sources would seem to be a resource that would be quite valuable going forward.

Whether that turns out to be the case or not, however, depends on what applications broadcasters or those who control the spectrum 25 years from now put on the channels licensed to them. A lot will depend on what broadcasters do over the next few years as to whether they are still the licensees of that spectrum 25 years from now.

What will happen to the spectrum in the political process? I’m not in possession of such a good crystal ball that I can divine that. Broadcasters, however, need to think about their businesses as bifurcated. It used to be that owning a broadcast license was a license to deliver content, and that was the only way to get that content to consumers.

Now, that is no longer the case. Broadcasters can deliver content through other avenues, such as cable and satellite. The continued carriage of their signals through those delivery media will depend on their creating content that’s so compelling for their communities that their communities won’t want to be without it and on their communities demanding of those gatekeepers that they deliver that content.

At the same time, broadcasters have to transmit a channel that they can use to deliver content and they might be able to use to deliver other types of information. Whether they will be allowed by the political process that controls the spectrum to do so over the long term will depend on what the broadcasters choose to do with the spectrum and on how the political process trades that use off against the other economic realities that might come to bear on that spectrum.

To read the first part of this interview, visit:

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