Re: [USRP-users] B210 dual channel operation with length tag in GNU Radio

[Ian Buckley via USRP-users]

Felix, Are you adding an explicit “tx_time” tag( with associated identical time tuple value) in both streams at the same offset as the TSB tag you are adding? I don’t think you can safely assume the TSB tag (Which causes bursting behavior in the USRP, equivalent to the use of the sob/eob) tags will cause both bursts to start at the same exact absolute time value. (Ready to be corrected by a GR guru on that….) Regardless attached is a simpler flow graph that uses streaming rather than bursting to achieve same effect you are looking for. The UHD sink guarantees to start two MIMO streams simultaneously for this kind of flow graph style. -Ian

felix.grc
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On May 2, 2018, at 7:27 AM, Wunsch, Felix (CEL) via USRP-users <usrp-users@lists.ettus.com> wrote: Hi all, I'm currently trying to emulate switching between two TX antennas using a B210 and GNU Radio. Unfortunately, there seems to be a delay between the two streams. The simplest MWE demonstrating my problem comprises two vector sources where source A repeats X (e.g., 1000) ones to emulate the ON state and then X zeros to emulate the OFF state. Source B works the other way round, i.e., first X zeros then X ones such that when the signals overlap during transmission, only one antenna is supposed to be "active". Each stream runs through a "stream to tagged stream" block with  a burst length of 2X (or a multiple thereof) and is finally fed into a (single) UHD USRP sink with num channels = 2, a matching TSB tag name, and a moderate sample rate of 1 MSps. There are no U's or other letters appearing in the console output. When I observe the resulting time domain signal with a second, independent USRP in the same flow graph, there seems to be a 45us delay in the second stream.  In the signal, it results in a small gap of 45us between when the first antenna connected to source A goes off and the second switches on and then a small overlap of the same length at the end of the second antenna's signal connected to source B. This repeats over the entire receive signal and does not seem to change in any way. I also restarted devices multiple times, the delay seems to be always the same. So now the obvious question: Where does this delay come from and how do I get rid of it? My application requires exactly time-aligned streams. I'm thankful for suggestions! Cheers, Felix _______________________________________________ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com

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