At 6:33 PM -0500 11/12/06, Manfredi, Albert E wrote:
Bob Miller wrote:I didn't spell it out but all the conversations I have been privey to suggest that broadcasters would be using MPEG4 with any A-VSB robust mode which makes all current receivers incompatible.Well, then that's a completely different discussion, isn't it. We were talking about the technical aspects of A-VSB, not how some particular broadcasters might want to use it.
No it's the same discussion Bert. It really does not matter what kind of decoders are in the legacy receiver, if it cannot understand the A-VSB bits.
Any receiver designed to understand SRS and STS, can also be designed to use new codecs. But there is NOTHING you can do to take advantage of these new tools in legacy receivers.
So as Bob says, in the end we may see a U.S. broadcast system that delivers one MPEG-2 encoded stream using the standard 8-VSB tools for legacy receivers, and the rest of the bandwidth used to deliver something new that is only backwards compatible, in that it does not break the stream for the legacy receivers.
So compatibility issues are by no means the sole province of ATSC.
Correct. The world keeps evolving quite rapidly. So the real challenge is to introduce new services that do not break existing services, but give the consumer a good reason to invest in the new receivers.
From this perspective, those in Europe who want to invest in an HD capable display will have the option of buying a new STB that delivers multiple services. Or they can invest in portable and handheld devices that take advantage of other new services.
Meanwhile here in the U.S., consumers will be able to invest in new receivers that may actually improve reception of DTV, including HDTV programming, however, this will come at a cost in quality to the programming that is staved for bandwidth like HDTV. Or they may be able to buy devices that will receive A-VSB broadcasts, that do not need HDTV image quality.
So in Europe consumers are being given more options, that need only be exercised if they want more services. In general the trend is toward improved services and image quality, relative to "First Generation DTV." Meanwhile here in the U.S. consumers are being given the option of actually receiving DTV reliably, or investing in new devices that are portable/mobile, but the trend is toward reduced services and image quality.
I'm saying, that 1.5 Mb/s, using let's say A-VSB in 1/4 rate STS mode, does not in any way make the remaining 13 Mb/s less robust or incompatible with all existing receivers. And, of course, that is only the worst case example.
No Bert, that's the BEST CASE example, or at least very close to it. We may learn that we can reduce the SRS overhead slightly, but it will clearly reduce the overall payload significantly. And we may find that we can use 1/4 rate STS rather than 1/2 rate. It's still a bit early to tell just how much of the payload we need to gain improved reception and ONE STS stream, but Best case we will probably lose 3-4 Mbps.
The worst case example is when the broadcaster decides to leave only 3-5 Mbps for the legacy service, and use the rest of the bandwidth for multiple STS streams.
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