Hi Tom, Matt replied inline:
On Wed, Feb 17, 2010 at 10:26 AM, Tom Rondeau <trondeau1...@gmail.com>wrote: > On Tue, Feb 16, 2010 at 5:45 PM, Srinivas <psriniva...@gmail.com> wrote: > > Matt, > > > > Thanks for verifying the data rate calculation! > > > > I tried the other solutions that you suggested, namely, > > > > - increasing the data rate by a factor of 2 or 4 > > It works. > > > > - modifying the OFDM code to widen the search range - How do I widen the > > search range ? > > Should I be looking in the "ofdm_sync_" blocks in "blks2impl" folder ? If > > yes, which synchronizer is currently used with ofdm_examples ? > > You need to add an argument to gr.ofdm_frame_acquisition in > ofdm_receiver.py (in python/gnuradio/blks2impl). > > In the current Git master, this is located on line 109 of > ofdm_receiver.py. After the "ks[0]" argument, you can put in an > integer. This is the maximum number of bins the receiver will search > over for correlation. It defaults to 10. > > I added this extra argument and tried changing the values from 10 to 100. I also tried with "int(0.5*occupied_tones) " as the argument, but it doesn't receive for lower data rates (< 1M). Only when I increase the data rate > 1.2M, I start receiving some pkts. As mentioned before, when I compensate for the frequency offset at the receiver it starts receiving packets successfully too. > - locking the usrps to a common reference > My usrp2s are located wide apart so I guess this solution is not practical. > > Besides, this confirms that the problem is somewhere in the USRP2 board, > right ? (as I tried swapping the daughter cards & firmware with the working > pair) > > Thanks, > Srinivas Nope, this is typical of radio hardware. They are always off > frequency. If two oscillators are off frequency and then multiplied up > to another frequency, the difference will also be magnified. So a 2.4 > GHz board will have a larger frequency offset than if you ran it just > through the BasicTx/Rx boards (even though the ratios should be the > same). > > Tom > Thanks! I understand this now. -- Srinivas WINLAB, Rutgers University New Jersey
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