[opendtv] Re: New Thread: What becomes of Legacy Analog Equipment
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Tue, 27 Nov 2007 13:29:15 -0500
Craig Birkmaier wrote:
> All you are able to relate is that the ATSC system has become
> usable by a handful of laggards who are unwilling or unable
> to pay a monthly subscriber fee for their TV fix.
Uhhh, yeah, just as DVB-T. What's your point?
> What will happen to the image quality of programming if and
> when broadcasters decide that they want to reach portable and
> mobile receivers?
They can either use schemes like A-VSB or MPH, or they can use DVB-H on
dedicated frequencies. Assuming that model survives. And unless OTA TV
is deliberately written off by those entrusted to use this slice of
spectrum,, for reasons that have nothing at all to do with modulation,
one can predict that ATSC, just like DVB-T, will continue to evolve. Not
just at the physical layer, as BOTH are doing now, but higher layers
too.
John Shutt wrote:
> Combine 1999 guard interval performance of DVB-T, add in 2007
> blind equalizers, and what do you get? Still something far
> superior to ATSC.
Not really. What you are ignoring is that if you go to the trouble of
using powerful equalizers in COFDM receivers, you still need to support
legacy receivers out there. One of the big benefits of depending more on
equalizers and less on pilots is that you get a lower peak to average
ratio. If you add powerful equalizers to some COFDM receivers, you'll
still need hundreds of full power QAM active carriers, 8K mode, or
dozens in 2K mode.
So in fact, by adding more powerful equalizers to existing DVB-T
receivers, you won't get the best of all worlds, as you seem to believe.
Not unless you change all the existing receivers out there first.
> ATSC still cannot do mobile at all, and the A-VSB and E-VSB
> schemes proposed come with a much higher bitrate hit than DVB-T
> HM.
All of these are half-truths.
First off, mobile 8T-VSB is certainly possible, and was demoed many
years ago already, and it can be made far better with the sorts of
techniques we have discussed on here from time to time. Secondly, when
you "compare" A-VSB with HM COFDM, as we have already discussed, John,
you have to look at the C/N margins and the capacity of each subchannel,
BOTH. They go hand in hand. And you can't draw conclusions by looking at
only the most robust, 1/4 rate A-VSB mode. I'm too lazy to do this
again, but the C/N margins for the robust stream in HM is something like
9 to 11 dB of C/N, compared with 4 dB for the 1/4 rate A-VSB. And then
you need to look at the wide channel too. How much bit rate and the C/N
margin of that.
> DVB-T still has a full continuum of bitrate vs. robustness
> that is settable by each individual broadcaster to meet their
> perceived needs. ATSC does not.
If the robustness of 3.3 b/s/Hz reception in one scheme starts
approaching that of 2.0 b/s/Hz reception in the other scheme, will you
still worry so much about this continuum of yours?
Fact is, DVB-T2 is being developed to allow modern technologies to
address some of the tradeoffs previously made in COFDM. I would expect
8-VSB to go through similar updates, as indeed is happening with A-VSB,
MPH, and numerous other schemes being proposed and pursued now.
But the absolutely MOST IMPORTANT point you continue to miss, John, is
that WE DON'T HAVE DVB-T IN THIS COUNTRY. So all this talk is academic.
At what point will you reconcile yourself to this fundamental fact of
life?
Bert
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