Matt, There was a frequency offset of ~30 KHz at the Rx w.r.t Tx so I compensated for it and it worked!.
The settings I am using is as follows: ./benchmark_ofdm_tx.py -f 2.45G --tx-amplitude 0.9 -M 8 -s 200 -m bpsk --fft-length=512 --occupied-tones=80 -i 64 --tx-gain=10 --cp-length=128 ./benchmark_ofdm_rx.py -f 2.45G -m bpsk --fft-length=512 --occupied-tones=80 -d 64 --rx-gain=20 --cp-length=128 I calculate the data-rate for OFDM as follows Data rate R = (ADC sampling rate x Occupied Tones) / (Nfft x Decimation) For the above setting it is 244 KHz. Am I right with the data rate calculation ? Thanks very much for your time, On Thu, Feb 11, 2010 at 10:26 PM, Matt Ettus <m...@ettus.com> wrote: > On 02/11/2010 04:45 PM, Srinivas wrote: > >> Hi All, >> >> I have 2 pairs of USRP2s with GNURadio-3.2 installed on their hosts. On >> one pair I am able to successfully run OFDM (benchmark_ofdm_tx & rx) >> with almost 95+% packet success rate. However on the other pair I am not >> receiving even 1 packet! >> >> I am using the same host machines and scripts. I also tried swapping the >> daughtercards (XCVR2450) and the firmwares with the working pair, but >> the problem remains. >> >> Does any one have a clue of where the problem might be ? >> >> PS: The received signal spectrum (usrp2_fft.py) on one of the >> non-working USRP2s is attached herewith. Besides this I plotted the >> spectrum of the received data from usrp2_rx_cfile.py at the receiver >> using MATLAB. The spectrum is of the same shape and strength as >> usrp2_fft.py displays. >> > > > Srinivas, > > It looks like you are using a very narrow signal. The frequency offset of > the USRP2s giving you trouble may be enough that you are outside of the > search range of the OFDM receiver (which is a percentage of the bandwidth of > the signal). > > You could try any or all of the following: > > - increasing the data rate by a factor of 2 or 4 > - modifying the OFDM code to widen the search range > - locking the usrps to a common reference > - measure the frequency offset of the transmitter, and run the receiver > with the actual frequency. For example, if the receiver sees the signal 30 > kHz high using usrp2_fft.py, call the ofdm receiver with > > -f 2.450030G > on the command line > > > Matt > -- Srinivas WINLAB, Rutgers University New Jersey
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