[opendtv] Re: Rai is doing DVB-T2 tests at 45 Mbps
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Tue, 24 Mar 2009 17:56:02 -0400
John Shutt wrote:
> I believe that 45 Mbps is the raw throughput, not the net payload.
>
> As such, 8-VSB in a 6 MHz channel delivers 32 Mbps including FEC.
Hmmmm.
8-VSB (no T in there) should provide a raw bit rate of 32.28 Mb/s
without any FEC at all. If you add the trellis code and the RS(188/208)
code, you cut that down to 19.45 Mb/s, and then some more reduction due
to framing and the training sequence.
In the article, they did mention at least a 3/4 FEC, which is the LDPC
code, I assume. So they may not have the whole overhead picture, but I
don't think they meant raw bit rate.
The ATSC comparison would be if we invented a terrestrial form of
16-VSB. You could achieve a raw 43 Mb/s in a 6 MHz channel, then cut
that down to 32.28 with a 3/4 rate code of some kind (LPDC or turbo
code), and you'd have achieved 5.38 b/s/Hz.
The difference is probably due to the steeper slopes of the band when
using 32K COFDM.
But even here, without some idea of robustness, the numbers aren't that
useful.
Bert
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