[vdr] Re: vdr-1.3.4 autopid and DVB-T

[Marcel Wiesweg <marcel.wiesweg@gmx.de>]

Am Donnerstag, 12. Februar 2004 16:34 schrieb Klaus Schmidinger:
> Marcel Wiesweg wrote:
> > Am Mittwoch, 11. Februar 2004 18:41 schrieb Koen De Vleeschauwer:
> > > While playing around with vdr-1.3.4 and the "autopid" feature, I
> > > noticed that sometimes vdr changes channels to values which seem wrong.
> > >
> > > Questions:
> > > - Is my analysis correct?
> > > - If it's correct, has this been solved already?
> > > - If it hasn't been solved already, does anyone have code for vdr-1.3.4
> > > which dumps all PSI information?
> > >
> > > thanks.
> > >
> > >
> > > When tuning to a DVB-T transponder which emits multiple NIT's, vdr
> > > seems to sometimes select the wrong NIT. As a result, when you're tuned
> > > to one transponder vdr may changes parameters of other transponders to
> > > values which correspond to a different location than the one you're in.
> > >
> > > Here I have three transponders. One (834 MHz) is part of a SFN, a
> > > single frequency network. The same frequency is used throughout the
> > > country. The transponder does emit 13 NIT's, corresponding to 13
> > > geographic regions, but all NIT's include a transponder at 834 Mhz
> > > (since it's a single frequency network). Right now vdr checks whether
> > > the NIT contains the frequency we're tuned to. But since the frequency
> > > is the same in all 13 regions, this test is always true. So vdr chooses
> > > one NIT more or less at random, and starts changing transponders based
> > > upon that choice.
> >
> > It seems that the SI mechanisms used for DVB-T are more complex than
> > DVB-S/C and non-trivial to implement.
> > A complete solution will probably have to use some descriptors among
> > Service Availability Descriptor, Cell frequency link descriptor, Cell
> > list descriptor,  Frequency list descriptor,  Linkage Descriprot
> > (linkage_type == 0x08) with knowledge about the longitude/latitude of the
> > current position :-)
>
> I don't believe that an STB needs to know the longitude/latitude of the
> current position. If you buy any commercial DVB-T STB and turn it on, it
> also has to be able to get the correct channels, without knownig where it
> is - or does it?

 I just had a look at the Cell list descriptor which provides this information 
(I don't know whether any broadcast uses it, in the end I'm neither living 
near Berlin nor do I have DVB-T hardware).
I'd like to know how this is supposed to work, somehow you need to know which 
NIT is the right one. Maybe offer a menu to choose the right network if 
multiple NITs are available and the current transponder is contained in more 
than one of them?


>
> Klaus



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