DAB with GNU Radio

GNU Radio
1

Hello everybody,

we would like to implement a DAB receiver with GNU radio. On the
hardware side we have a USRP with the TVRX daughterboard. From some
older posts on this list, i learned that there are already some people
trying to do this.
Is there any initial advice or pointers to existing implementations you
could give us? Do we need the checkout the svn version or even some
branch or is the ‘latest stable’ enough?

Any help is very appreciated!
Thanks in advance,
Chris

2

Hello Chris

we would like to implement a DAB receiver with GNU radio. On the
hardware side we have a USRP with the TVRX daughterboard.

Jens E., who worked on DAB some time ago, found out that the TVRX
actually disturbs the OFDM signal very much, making it rather hard to
receive DAB, so I would strongly discourage its use (I’m not able to get
any information out of TVRX samples currently).

My current setup involves a spectrum analyzer to receive the signal, and
an external mixer+signal generator to convert from the IF of the SA down
to 10 MHz for the BasicRX. I have uploaded some of the samples to [1].

If you have a DAB station in the L-Band near you, you can also use the
DBSRX. (@Jens → is it ok if I publish your mode 2 samples as well?).

From some
older posts on this list, i learned that there are already some people
trying to do this.

I have implemented part of DAB for my current semester thesis. I have a
working physical layer (all OFDM stuff, all 4 DAB modes complete for
transmitting and receiving), and enough of the FIC (fast information
channel) to see the names of the radio stations (receiving+some blocks
for transmitting; all modes). To actually hear something, the MSC
(main service channel) would be needed (many blocks in the MSC already
exist, as they are needed for the FIC too, so it should not be that much
work).

Is there any initial advice or pointers to existing implementations you
could give us? Do we need the checkout the svn version or even some
branch or is the ‘latest stable’ enough?

I have uploaded my current code to [2]. It requires GNU Radio from the
trunk and some small patches (mainly for the peak detector). If you are
interested, I can also send you my mostly-finished semester thesis
off-list.

I hope to finish the FIC in the next week or so, but as my thesis is
over at the end of this week, I am not sure, when/if I’ll get to the
MSC. The code for OFDM and FIC currently runs real-time on my four year
old ThinkPad (Pentium M 1.6 GHz).

Regards, Andreas

[1] http://people.ee.ethz.ch/~andrmuel/files/gnuradio/samples/
[2] http://people.ee.ethz.ch/~andrmuel/files/gnuradio/gr-dab.tgz

3

Hi Andreas,

I am also interested in your work. Would you be so kind of sending me
your
thesis when it is finished?

Thanks a lot!

Best regards,
Carles Fernández.

4

Christoph Fischer wrote:

any information out of TVRX samples currently).

That is bad news… So perhaps at first we should do some analysis if
DAB is really impossible with the TVRX or if we only have severe
degradation of SNR. We have a DAB transmitter just some km away from the
university so perhaps it could somehow work at least for this one…
Does anyone already have some data about the phase stability of the
TVRX? Unfortunately the L-Band is no option here.

You could try undersampling with basicRX.
Frequency stability wouldn’t be an issue. But the sensitivity is very
very low and you get interference from all bands above 32 Mhz folded
over
each other.

This could be improved by using a bandfilter and an amplifier in front
of the basicRX.
Just use a bandfilter which only passes the part of band III which you
are interested in.
The bandfilter should have a bandwidth of 30 Mhz or less.
For example 170 - 200 Mhz.

For amplification best would be a dedicated amplifier for this freq-band
with 20 to 50 dB gain.
But to keep things simple you could use an off-the-shelf amplifier for
TV-signals which have usually 10 to 15 dB gain.

As an antenna you could use a home-made vertical dipole or J-antenna for
exactly the right freq.
This also improves selectivity.

greetings,
Martin

5

Hello Andreas,

thank you for your very interesting reply.

we would like to implement a DAB receiver with GNU radio. On the
hardware side we have a USRP with the TVRX daughterboard.

Jens E., who worked on DAB some time ago, found out that the TVRX
actually disturbs the OFDM signal very much, making it rather hard to
receive DAB, so I would strongly discourage its use (I’m not able to get
any information out of TVRX samples currently).

That is bad news… So perhaps at first we should do some analysis if
DAB is really impossible with the TVRX or if we only have severe
degradation of SNR. We have a DAB transmitter just some km away from the
university so perhaps it could somehow work at least for this one…
Does anyone already have some data about the phase stability of the
TVRX? Unfortunately the L-Band is no option here.

Is there any initial advice or pointers to existing implementations you
could give us? Do we need the checkout the svn version or even some
branch or is the ‘latest stable’ enough?

I have uploaded my current code to [2]. It requires GNU Radio from the
trunk and some small patches (mainly for the peak detector). If you are
interested, I can also send you my mostly-finished semester thesis
off-list.

Thank you very much for all that. We also would be very interested in
your thesis.

Regards,
Chris