[linux-dvb] DVB-T devices supporting hierarchical mode?

Mauro Borghi mauro.borghi at TILAB.COM
Wed Feb 15 17:09:02 CET 2006


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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