What is this, an annual unthinking pronouncement of yours? You've been
predicting such radical changes for about 9 years, and none has happened.
It certainly won't happen on your suggestion.
If the modulation scheme doesn't work well enough, a new modulation scheme
won't replace 8-vsb; television will just die, becoming non-existent in a
media world with many new choices.
Nobody wants to replace the embedded base of receivers, Bob. No broadcaster
will want to signal that receivers need to be replaced, since broadcasters
will be blamed for the message and cost of such replacement.
However, there is some room for maneuvering. Imagine, for example, if
error-free ATSC M/H transmissions could qualify as the free, SDTV-equivalent
transmissions required under the Act. I don't want to think too much about
what would have to come about to make this something broadcasters and their
viewers desired, but it is within the realm of possibility. However, such a
position would need to be nuanced; it obsoletes the billions of dollars that
consumers have spent on digital television sets and stbs.
John Willkie
-----Mensaje original-----
De: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] En
nombre de Bob Miller
Enviado el: Monday, January 12, 2009 9:45 AM
Para: opendtv@xxxxxxxxxxxxx
Asunto: [opendtv] Re: Kennard and Powell to the rescue
Within one year of the transition broadcasters themselves will be
asking for a better modulation.
Bob Miller
On Mon, Jan 12, 2009 at 10:14 AM, Manfredi, Albert E
<albert.e.manfredi@xxxxxxxxxx> wrote:
Tom Barry wrote:
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.
It would be nice to have the C/N margin requirements for the different
modes spelled out in A/153, however I would like to point out that some
applications of M/H could have more to do with compensating for lower
transmit power than more multipath, depending how it gets put to use.
John Shutt complained years ago that there's no way for a broadcaster to
reach its audience when it needs to cut its power for maintenance
reasons. This could be a way, and 1/2 rate would likely be just fine for
this application.
Anyway, Part 2, Table 6.1, says that if you want 1/4 rate for the entire
robust stream, you need to take 1.8 Mb/s of the 19.39 Mb/s in order to
provide one 312 Kb/s robust channel. That's still not unreasonable.
Or, if you insist on taking 0.917 Mb/s only from the 19.39 Mb/s, 154.6
Mb/s of 1/4 rate robust stream. That's probably not good for anything
but small screens.
Bert
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