[opendtv] Re: 20050627 Mark's Monday Memo
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 4 Jul 2005 19:22:01 -0400
John Shutt wrote:
> No, Bert,
>
> Like being able to go from 19 Kbps to 4 Kbps during the
> time we are at low power on our standby antenna while
> our main antenna is being serviced.
Again, starting from the premise that there appears to be
no movement by the FCC or the NAB to switch over to COFDM,
can what you are asking for be achieved with 8-VSB?
Check out the new Amendment 1 to ATSC standard A/53C.
This is where E8-VSB is incorporated now. By layering an
extra convolutional and RS block FEC on top of what's
already there, they achieve increased robustness.
According to Wayne Bretl, with 5th gen receivers, this
buys an extra 6 dB of C/N margin, IIRC (but it wasn't
clear with which FEC this was the case). With older
receivers, the improvement was greater.
If all of the bandwidth is dedicated to the additional
1/2 rate FEC for E8-VSB, then the channel capacity is
8.45 Mb/s. If all the bandwidth is dedicated to the
additional 1/4 rate FEC, then you get 4.23 Mb/s.
So in principle, this scheme could fit right in with
what you want to do. Or you can provide a mix of wider
and more fragile along with narrower and more robust
streams.
Bert
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