On Wed, 25 Apr 2012 12:01:33 +0800, Alick Zhao wrote: > On Tue, 24 Apr 2012 07:52:09 -0700, Nick Foster wrote: > >> >> Alick, >> >> You will have to instrument your flowgraph in order to find out. Add file >> sinks to different stages in the transmitter and receiver to verify that >> the data looks as expected. You can use MATLAB or Octave to visualize the >> data. There are scripts in gnuradio-core/src/utils which will aid you in >> loading sample data into MATLAB. Verify that the frequency offset is within >> bounds and being handled appropriately. Verify that clock recovery is >> keeping a lock on the incoming data. >> >> --n
I also make some plots with the logged data. I can see that consecutive 1000 points of data after freq_recov or time_recov are distributed around the unit circle. I think the freq/time recovery may not work well. Given static indoor environment, the coherence time should be long. I'd expect that the constellation points after timing recovery should stay around two certain points for some thousands of samples. Is it so? If the problem is with the recovery loop, I wonder how I can adjust the parameters of the loop. I have read Tom's post about loop gain values[1]. It seems that damping factor (0.707) should not be changed, and loop bw is somewhere around pi/100 to 2*pi/100. So I find little change can be done. By plotting data directly output by usrp source I find that the constellation points are disperse too. But I think it is due to lack of synchronization between tx/rx. Am I wrong about this? [1] http://www.trondeau.com/blog/2011/8/13/control-loop-gain-values.html -- alick Fedora 16 (Verne) user https://fedoraproject.org/wiki/User:Alick _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio