This has never been clear to me! What about the phase ambiguity due to the fractional-N VCO's, as Marcus has mentioned?
This has to be calibrated out, yes/no?, but how?, unless after a retune you then TX a calibration sequence that you can correlate against and correct. But after this, then, do you really need to accurately wait for a PPS? It's just stuff in the buffer, with the computational overhead of alignment. Basically, how do you compensate for the ambiguity? (maybe it doesn't matter and I'm probably talking rubbish :-/ ) Cheers ----- Original Message ---- From: Josh Blum <j...@ettus.com> To: Khalid Jamil <khalid.ja...@gmail.com> Cc: discuss-gnuradio@gnu.org Sent: Tue, 26 April, 2011 21:12:08 Subject: Re: [Discuss-gnuradio] Synchronization issue with multiple USRPs On 04/26/2011 11:22 AM, Khalid Jamil wrote: > Please correct me if I am wrong. I think that this random channel-channel > phase offset at each acquisition depends on when each usrp 100MHz LO locks > to 10MHz external frequency reference by PLL. How PPS will help in that > case? Unless PPS is locked somehow to 10MHz clock? > Yes, but I strongly recommend that you get time-aligned samples working before trying to calibrate for the LO phase offsets. In your GRC flowgraph, each USRP source block will provide samples that start at a different random time that could be offset by many milliseconds. I don't think you want that? In order to get time-aligned samples from N devices, you must 1) synchronize the the time registers (seconds/ticks) across all USRP devices. You should use the PPS to do this 2) tell the devices to stream at the same time. > Is there a good example to follow, may to start with 2 or 4 channels? > There is an example that comes w/ uhd called rx_multi_samples. if you want to do this in GRC, follow the instructions in the previous email. -Josh _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
