Hi Ernest, Although this explains why the system breaks when the noise becomes large (~10dB) and so the overall signal amplitude increases beyond (~1), it cannot explain why the system does not recover AFTER all amplitudes are set back to normal values (~1) and noise back to -30dB ...
It was my impression that the polyphase sync block will completely reset once it sees a tag from the correlate and sync block, but this does not seem to be the actual behavior... Achilleas On Wed, Jul 10, 2019 at 12:16 AM Ernest Fardin <efar...@ieee.org> wrote: > Hi, > > I think this behaviour may be due to the level into the Polyphase Clock > Sync block. The block expects a signal amplitude of 1 as explained in [1]. > > An AGC between the Correlate and Sync and the Polyphase Clock Sync blocks > might do the trick. > > Cheers > > Ernest > > [1] https://destevez.net/2017/08/agc-for-gr-satellites/ > > > On Wed, Jul 10, 2019 at 6:22 AM Achilleas Anastasopoulos < > anas...@umich.edu> wrote: > >> Hi all, >> >> I am not very successful in running the uhd_corr_and_sync_tx/rx.grc >> example in the gr-digital examples directory (3.7.13.5) using usrps. >> >> In an effort to debug it, i merged the two graphs and eliminated the uhd >> sink/sources (see attached) and so I am running a simulation without the >> usrps. I also eliminated the FLL block as I do not have any frequency error >> and not even any noise. >> >> The behavior I see is as follows: >> >> The transmission seems fine (a nice rrc spectrum followed by silence >> periodically on and off). >> On the reception side the blocks seem to be working fine producing >> appropriate tags (one every 20Ksamples as expected) which means that the >> "correlate_and_sync" block works as expected. >> >> When I plot the output of the "polyphase_clock_sync" I expect to see >> three clear points: +/- A and 0. Indeed this is what I see at first. >> >> Now I do the following: I increase the noise for a while to a large >> number (~10dB) and then I take it back almost to 0 (-20dB). From that point >> on, although the "correlate_and_sync" block works as expected (I see the >> tag offsets back to normal) the picture does not contain three clear points >> but is blurred indicating that the "polyphase_clock_sync" does not work >> appropriately and I can never recover from this. >> >> I was hopping that since the "correlate_and_sync" block recovers and adds >> the appropriate tags to the stream, the downstream block can recover as >> well. However the behavior is not as robust as I expected. >> >> Can someone shed some light into this. >> >> thanks >> Achilleas >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >
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