[linux-dvb] DVB-S2 Multiple logical TS on the same frequency

Manu Abraham abraham.manu at gmail.com
Tue Oct 16 19:07:43 CEST 2007


Francesco Schiavarelli wrote:
> Manu Abraham wrote:
>> I guess it uses FEC short Frames and a Rolloff of 20%.
>> Currently we use FEC normal frames and a Rolloff of 35%. I will check
>> on this though.
> 
> Do you mean Rolloff and FEC type are somehow hardcoded in current
> linuxtv STB0899 driver?

Currently with CCM, we never had to worry about FEC long or short frames 
as it is always normal (LONG) frames with regards to CCM.

The STB0899 driver doesn't take rolloff as a parameter from either from 
the user in the form of the S2 delivery system descriptor, or from a config 
file.

It is in fact extracted from the Baseband header and used, thereby leading 
to "no" assumptions, in some cases the the SI can be wrong or missing, but 
the BaseBand header, not. So the STB0899 relies on a reliable method of 
extracting the rolloff and hence thereby the bandwidth of the same.

> If needed I can ask and provide here more detailed transmission
> parameters regarding this transponder...

This would be great, much appreciated.
 
>> It looks like a DSNG profile, some uplinks as far as i can guess.
> 
> I can confirm that this feed will be used by local terrestrial DVB-T
> transmitters, if I understand correctly your guessing.

Yes, that is what i understand too. This profile uses ACM, well i need more 
inputs to have this implemented (ie this is currently an unimplemented 
feature, although it can be implemented)

the advantage of using ACM is to maximize the transponder bandwidth 
(remember transponders don't come cheap) You can think of ACM in a 
similar way as how statistical multiplexing (VBR) is done, eventhough the 
entire transponder eventually is CBR, just that the distribution is more 
optimized.

This part needs some more clarity, that's what exactly it is. I have requested 
for some larger chunks of information from whatever sources i have, but don't 
rely on that alone (try to get whatever info, what you can), the more sources 
we have, the more we can have it implemented in a more robust way. Though 
it means some more large discussions going on.

Manu




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