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Re: [Discuss-gnuradio] DVBT Tx

From: Jens Elsner
Subject: Re: [Discuss-gnuradio] DVBT Tx
Date: Mon, 5 Mar 2007 08:52:22 +0100
User-agent: Mutt/1.5.9i


I did some experiments with DAB which is, (due to differential
modulation), simpler than DVB. On the PHY level I managed to get
"almost" (about 60%) real-time performance on my P4 with GNU Radio
and prerecorded samples.

This was only PHY (even without channel coding!), and the
synchronization algorithm used was pretty shaky. Channel coding eats
up a lot of resources as well, look at the throughput figures for

DAB has a bandwidth of 1,5 MHz, DVB more than 5 MHz. All in all considered,
my guess is that 5-8 years from now it might be possible to do these kind
of bandwidths on a general purpose processor. But this is just my 
unjustified guess. :-)

When starting to work on DVB, you'll have to write a transmitter chain 
and a receiver separately, to you can test both. Just look at the 
GNU Radio examples. I would suggest to limit your final thesis to the
PHY layer first - OFDM synchronization by itself is a real challenge.
What I noticed is that, due to the way transmission protocols are
designed, there is not "one solutions fits all" approach. You would
have to tailor available OFDM code to the specific needs of DVB (DAB).
A good way to start might be the new GNU Radio OFDM code available
from trunk. 

A good way to "get a feeling" for real data might be to look at it in
Matlab or Octave. You could test signal processing algorithms in such
an enviroment as well.

Best regards,

> I am a telecommunication engineering student in italy at Pisa University
> (Italy) at the moment, and it is quite likely that my final thesis (to be
> started in about a year from now) will be a DVB-T transmitter.
> So I'm slowly approaching the subject, and starting to figure out some
> preliminary choices  and possibilities...
> My  first  questions  then are :
> ..Do you think it is possible to reach real time, considering hardware
> improvements  since the video was recorded?

> ..How  could  I  test a non  real  time  transmitter?  (I  think  I
> understand  not   real  time  receiver but how did you test the
> transmitter?)
> Best Regards
> -- 
> Vincenzo Pellegrini

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