Thanks for the reply Patrik, I managed to identify parameter values that make OFDM decoding work. It seems that low decimation/interpolation rates don't work (a bunch of "S"s at the receiver), nor do higher modulation schemes. The performance is very sensitive to the fft_length/occupied_tones.
As a side note, the OFDM example from gnuradio-3.2.2/gnuradio-examples/python/ofdm works with BPSK but doesn't deliver any correct packets with the other modulations. The example I made in GRC though, works fine with both BPSK, QPSK and 8PSK. However, the packet error rate is quite high, I still haven't identified a case in which the error rate would be less than %40. cheers, Veljko 2010/1/15 Patrik Eliardsson <patrik.eliards...@foi.se>: > Hi, > > I've tried the OFDM example on the USRP2 with minor changes and I didn't > encounter any problems. Be sure that you have the same FFT-length, number of > occupied tones, interpolation/decimation on both the receiver and > transmitter. Have you tried to increase the distance between the transmitter > and the receiver? Depending on your surrounding environment you may have to > tweak the length of the CP. > > I have the same configuration as you, but I have the RFX2400 instead of the > XCVR2450. > > Regards, > Patrik Eliardsson > >> -----Original Message----- >> From: >> discuss-gnuradio-bounces+patrik.eliardsson=foi...@gnu.org >> [mailto:discuss-gnuradio-bounces+patrik.eliardsson=foi...@gnu. >> org] On Behalf Of Veljko Pejovic >> Sent: Wednesday, January 13, 2010 10:22 PM >> To: discuss-gnuradio@gnu.org >> Subject: [Discuss-gnuradio] OFDM modulation/demodulation over USRP2 >> >> 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 >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
