[Noisebridge-discuss] Disaster Recovery SDR-based mesh

Matthieu Tourne matthieu.tourne at gmail.com
Fri Sep 13 06:47:53 UTC 2013


On Thu, Sep 12, 2013 at 7:33 PM, Marc Juul <juul at labitat.dk> wrote:

> Hi!
> Some of us at sudo room / east bay mesh are working on a low bandwidth
> disaster recovery mesh project based on software defined radios.
> We're prototyping with a combination of USRP1 and RTL-SDR devices and GNU
> Radio.
> We're having some issues getting the receivers to demodulate our data
> streams (using DQPSK and QAM modulation).
I never thought about doing much more than tuning to FM radios with my
rtl-sdr, but that's a pretty cool project!

I think that depends what's your goal, if you want to decode qpsk frame
from classic radios [1] I think rtl-sdr can do it.

If you want to Tx/Rx data accurately, I think you need a digital modulation
chip [2]
(my understanding is that it works best at the hardware level if you want a
decent bandwidth)

Something like this [3] could help, if you know someone who can program
fpga cards ..

But it's a pretty cool project, maybe you can use an OFDM stream instead
That's the hd tv data stream the chip RTL2832U [5] in the rtl-sdr is meant
to demodulate in hardware.

.. I even found an opencore for ofdm modulation [7], which could (in
theory) be loaded on an fpga ..



[1] http://en.wikipedia.org/wiki/Project_25
[2] http://www.maximintegrated.com/app-notes/index.mvp/id/686
[3] http://nuand.com/
[4] https://en.wikipedia.org/wiki/Orthogonal_frequency-division_multiplexing
[5] https://www.youtube.com/watch?v=TQ0KDjxhXNk
[7] http://opencores.org/project,ofdm
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