[opendtv] Re: 4K TV over DVB-T2 experiments
- From: Albert Manfredi <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Sat, 13 Mar 2010 19:17:59 -0500
Olivier Houot wrote:
> In case this was not already mentionned here,
> details can be found on the DVB website:
http://www.dvb.org/news_events/dvbscene_magazine/DVB-SCENE33.pdf
> What was broadcasted was 3840x2160p/25.
> The source was a RED camera.
> The data was broken into four standard HDTV
> streams, the nominal capacity of an 8 Mhz
> DVB-T2 multiplex. In the future they intend to
> do it all in one stream using H.264 High Profile
> level 5.1.
That report describes the DVB-T2 modes used thus:
"Real transmission on channel 29 UHF from the Torino-Eremo transmission site
was carried out using DVB-T2 with the following parameters: 256QAM
constellation, 32K OFDM mode, and Guard Interval 1/128. Two different FEC
values were used in order to test two different configurations with a useful
bitrate ranging from about 36 Mbit/s (FEC 3/5) to 45 Mbit/s (FEC 3/4), ..."
...
"The DVB-T2 configuration with FEC 3/5 and 36 Mbit/s capacity required
approximately the same C/N ratio (16 dB for BER = 10-7) of one typical DVB-T
configuration (64-QAM, FEC=2/3, 24 Mbit/s capacity) while providing 50 percent
more capacity. The configuration with FEC=3/4, providing an 88 percent capacity
increase, required additional 4 dB (C/N=19.9 dB for BER = 10-7)."
Something seems odd, though. According to the RAI Research presentation,
http://www.fub.it/public/Morello020408B.pdf
Slide 35,
you're better off using 64-QAM for anything with 16 dB of C/N. And even then,
to achieve 35 Mb/s in the 8 MHz channel, they needed to use 5/6 FEC rather than
the more robust and bandwidth-hogging 3/5 FEC. My take is that the 16 dB C/N
they are hoping for is a bit optimistic. (Not that the BER makes a big
difference, since it degrades very rapidly when it starts degrading, but even
that seems odd. The BER criterion used in this paper was 10E-7, as opposed to
10E-4 in the presentation. That would make the criterion more difficult in the
4K test, implying less rather than more spectral efficiency.)
So here's the plan for doing 4K over ATSC. Since they have split the 4K image
into four HD streams, the quickest approach is to use two 8-VSB channels as is,
sending two HD streams over each one. Since these are 25p streams (in the US it
would be 24p), should be no problem. Of course, you're taking up 12 MHz instead
of 8 MHz, but you're still using H.262 compression and you're achieving a C/N
of 15.2 dB.
To reach 35 Mb/s in a 6 MHz (5.38 MHz) channel, you would have to go with
16-VSB, which gives a gross 40+ Mb/s in the 6 MHz channel. Then you would need
to adopt the LDPC FEC, and use no more than 7/8 FEC.
Bert
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