[linux-dvb] Re: Problem with scan app

[Johannes Stezenbach <js@convergence.de>]

On Tue, Dec 09, 2003 at 10:19:47AM +0000, jp wrote:
> 
> IMHO scan is too clever for its own good. It does it the right way(tm)
> but in practical terms not every transmitter is set up the right way.
> 
> Heck some transmitters don't even include the NIT.
> 
> The only safe approach is to try to scan each RF channel individually.
> (using scan -c)
> Sure this will take a while (there are ~46 RF channels used in the UK) 
> the first time, but once you establish what frequencies you
> need you can rescan them to pick up new channels/revised pids etc.

Yes, this should be implemented as a fall back strategy for DVB-T and
DVB-C. But because it usually takes more time it shouldn't be used
unless really necessary.

> The check "have I scanned this freq before?" combined with -n flag 
> should get you all channels.conf in a single pass assuming the 
> transmitter has a well-formed NIT.
> 
> In boundary areas, like where Gavin is, where the best signal comes from 
> one transmitter for some multiplexes and some from another, scanning 
> each possible freq and picking those with the better signal (by reading 
> SNR from the card if that is supported on your card) is the most 
> practical approach.

I think www.dvb.org has some interesting white papers about DVB-T,
and also about mobile DVB-T reception, just in case someone wants
to do some research. (Unfortunately I don't have time to read
them all by myself ;-( ).

And BTW, http://www.engr.sjsu.edu/rmorelos/ee252s03/WhyCOFDM.pdf
is a nice paper which explains how COFDM works.


Regards,
Johannes


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