[opendtv] Re: Kennard and Powell to the rescue
- From: "John Willkie" <johnwillkie@xxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Sun, 11 Jan 2009 17:42:12 -0800
There has already been testing done on this point, in the IDOV report, which
I read on May 14 of last year. The upshot was that -- before the system was
optimized -- M/P/H (now, in most contexts, M/H) needed 1/2 rate for handheld
devices in San Francisco. Not for automobile devices on streets, nor for
automobile devices on freeways.
It's all part of the bit-budget. How much do you want to spend in bits to
reach a particular market segment.
And, your calculation doesn't take into account other overhead elements,
including the pseudo-random data, the various mandatory elements, the tpc
and fic, and even the cost of doing something half-assed.
1 mbps is a non-starter. M/H is unlikely to ever be deployed in such a
context. Many SDTV only stations have 9 mbps or so free to play with.
Indeed, it's an absurd notion, perhaps the most absurd notion ever offered
here.
John Willkie
-----Mensaje original-----
De: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] En
nombre de Tom Barry
Enviado el: Sunday, January 11, 2009 5:29 PM
Para: opendtv@xxxxxxxxxxxxx
Asunto: [opendtv] Re: Kennard and Powell to the rescue
To me it seems equally likely because of 8vsb multipath that you will
need 1/4 rate FEC instead of 1/2 rate. And that more or less delivers
only half the usable payload, pretty much eliminating even mobile AVC
video if you started with only 1 mbps out of an ATSC stream.
- Tom
Manfredi, Albert E wrote:
> Bob Miller wrote:
>
>> So if all you take away from the main program is 1 Mb/s how
>> much of that is overhead and how much is for WHAT type of
>> video, MPEG2 or MPEG4? How many bits for this MPEG2 or MPEG4
>> low quality program? If its MPEG4 you will need a new receiver
>> right?
>
> The answer to the first question is in Table 6.1 of A/153. If you take
> away 0.917 Mb/s of the main channel, you can provide a 1/2 rate (over
> 2/3 rate) robust stream of 312 Kb/s capacity. So that gives you the
> extra convolutional code and the extra training sequences. Take away 1.8
> Mb/s capacity, and you have 629 Kb/s of robust capacity, at 1/2 rate.
> And so on.
>
> This (or these) robust stream(s) would all be H.264 compression.
>
> You would need a new receiver no matter what, if you wanted to be
> capable of receiving the M/H streams. So sure, you would need a new
> receiver. Initially, an added STB could take care of this, more or less
> manually. But eventually, CE manufacturers could also build this in more
> intelligently.
>
> Users of HD radio, for example, know that when the signal of the main
> digital subchannel falls below a certain threshold, HD radios seamlessly
> switch back to the analog FM signal. Only for the main digital
> subchannel, though. The other subchannels are allowed to go silent for a
> bit of time, and they the radio reverts to the analog signal.
>
> This same behavior could be programmed into sets with built-in M/H
> capability without any huge problems. If there's only one robust M/H
> stream offered, then only the main subchannel will failover to the M/H
> stream. If more M/H subchannels are offered, other streams would also be
> allowed to fail over.
>
> Bert
>
>
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