[linux-dvb] DVB-T devices supporting hierarchical mode?
mauro.borghi at TILAB.COM
Wed Feb 15 17:09:02 CET 2006
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
>> 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:
> 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!)
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