Hi Patrick,
my comments inline...
Patrick Boettcher wrote:
Hi Mauro,
On Tue, 14 Feb 2006, Mauro Borghi wrote:
For the first time here in Torino, RAI (Italy's public television
broadcaster) is broadcasting an experimental DVB-T channel, featuring
in high definition the Olympic Winter Games.
They are exploiting *hierarchical* modulation, in order to accomodate
-in the same radio channel- both a DVB-H test stream and this HDTV
stream.
The low bitrate DVB-H stream is the "high priority" stream, while the
HDTV stream (H.264/AVC) is the "low priority" one.
From the information I got from devices supporting hierarchical mode,
tuning data are as following:
RAIHD:538000000:INVERSION_OFF:BANDWIDTH_8_MHZ:\
FEC_1_2:FEC_3_4:QAM_64:TRANSMISSION_MODE_8K:\
GUARD_INTERVAL_1_8:HIERARCHY_2:x:x:x
Very interesting. I would have never thought that they will use
hierarchical transmission in the real world, but anyway.
It makes sense, however: on the same frequency you can host both a very
robust signal for mobile reception, and an high bitrate stream, which
needs a proper antenna to be received...
The high priority (low bitrate) stream in this case is around 5 Mbps -
enough to host 8 to 10 low-res services.
[intro end]
Do you know about LinuxDVB-supported devices which are known to
support hierarchical modulation?
Is it meant to be sufficient setting HIERARCHY_2 in the struct passed
to the frontend device when tuning, in order to select the LOW
priority stream?
Although it was most likely never tested with most of the
demod-drivers in linux-dvb it should be possible with all of them.
From the tests I did with a Twinhan 7045 USB2 clone (from digicom),
the device seems to always lock on the HIGH priority stream, no
matter what params are passed!
The Twinhan box has a MT352 inside and the controlling is done inside
the FX2 USB firmware. As hierarchical transmission has significant
drawbacks when used and no one (not even Twinhan :) ) expected that to
be used anywhere, they don't have it implemented. Ie. there is no way
to give this information to the firmware.
It would be interesting to see how devices perform.
As far as I can see, maybe too optimistic, only the vp7045 and
dtt200u-driver (Twinhan and Wideview Clones) are definitely not
supporting the reception of hierarchical transmissions. Every other
DVB-T demodulator driver has at least the option to set (if the
hardware works is another question).
I know that hierarchical transmissions are working with DiBcom
demodulators. Maybe the current dib3000mb/mc driver is not doing it
correctly, but the hardware works - in that case I could help to fix
the driver.
Thanks for this info!
In the next few days I'll try using an Hauppauge/Technotrend (Philips
tda1004x frontend), and let you know if it worked.
Unfortunately I do not have any DiBcom demod at hand...
(To make things worse, the signal is transmitted with vertical
polarization, while all the other DVB-T channels are horizontal: only in
the lab at work I have a suitable antenna system!)
Ciao,
Mauro.
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