[opendtv] Re: Kennard and Powell to the rescue
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 12 Jan 2009 10:14:12 -0500
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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