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[Discuss-gnuradio] OFDM modulation/demodulation over USRP2


From: Veljko Pejovic
Subject: [Discuss-gnuradio] OFDM modulation/demodulation over USRP2
Date: Wed, 13 Jan 2010 13:22:01 -0800

Hi,

I'm using Ubuntu 9.10, gnuradio version 3.2.2 and two USRP2 boards
with XCVR2450 daughter boards. The boards are about a meter apart from
each other.

I'm trying to get OFDM working over USRP2 boards and for that I'm
using GRC. I created a simple local loop (without USRPs):
signal_source->modulation->channel_model->demodulation->scope_sink. In
this case OFDM modulation/demodulation works fine. However, when I
split the loop into a sender signal_source->modulation->usrp2_sink and
a receiver: usrp2_src->demodulation->scope_sink the decoding does not
work, i.e. I don't get any output on the scope_sink. Although, FFT of
the usrp2_src output looks exactly like what OFDM should look like.
I'm pretty sure that the error is connected to OFDM as I got this
transmitter/receiver pair working with GMSK, for example.

I also tried the examples in
gnuradio-3.2.2/gnuradio-examples/python/ofdm which I had to tweak a
bit in order to get them using USRP2, but I got the same results:
there is an OFDM-like signal in the air, but it's not getting decoded.

Did anyone got OFDM demodulation working on USRP2? If so, any hints
are highly appreciated.

Thanks,


Veljko




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