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
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