Lukas, Just before receiving your email, I ran the following with my custom c++ & matlab software using X310/UBX-160 with the connections I described. The following shows the output which is very consistent. I used a 100 tone multi-tone waveform spread over 4 MHz bandwidth (using 5 MS/s sample rate on Tx and Rx). Note the consistency of results as I toggled between 2 frequencies: 2450 and 2460 MHz.
My method was the following: - Tx waveform was 500 points long - Rx capture was 5000 points long - Compute cross-correlation (using Matlab xcorr) as follows: xcorr(rx0, conj(tx)) AND xcorr(rx0,conj(rx1)) - Find the correlation peak (which was very pronounced) which shows the sample delay between the two signals. Extract the phase at the peak Oops, I just realized that I used a constant DSP freq (10 MHz) and I changed the LO freq in my test. I will try again with moving the DSP freq instead. Rob Test 1: freq = 2450.0 MHz Rx0/Tx0 xcorr peak at index 108 with phase -121.8 Rx0/Rx1 xcorr peak at index 115 with phase -95.7 Test 2: freq = 2460.0 MHz Rx0/Tx0 xcorr peak at index 108 with phase -58.7 Rx0/Rx1 xcorr peak at index 115 with phase 13.1 Test 3: freq = 2450.0 MHz Rx0/Tx0 xcorr peak at index 108 with phase -121.7 Rx0/Rx1 xcorr peak at index 115 with phase -95.8 Test 4: freq = 2460.0 MHz Rx0/Tx0 xcorr peak at index 108 with phase -58.6 Rx0/Rx1 xcorr peak at index 115 with phase 13.0 Test 5: freq = 2450.0 MHz Rx0/Tx0 xcorr peak at index 108 with phase -121.7 Rx0/Rx1 xcorr peak at index 115 with phase -95.8 Test 6: freq = 2460.0 MHz Rx0/Tx0 xcorr peak at index 108 with phase -58.8 Rx0/Rx1 xcorr peak at index 115 with phase 12.7 Test 7: freq = 2450.0 MHz Rx0/Tx0 xcorr peak at index 108 with phase -121.8 Rx0/Rx1 xcorr peak at index 115 with phase -95.9 Test 8: freq = 2460.0 MHz Rx0/Tx0 xcorr peak at index 108 with phase -58.7 Rx0/Rx1 xcorr peak at index 115 with phase 12.9 Test 9: freq = 2450.0 MHz Rx0/Tx0 xcorr peak at index 108 with phase -121.8 Rx0/Rx1 xcorr peak at index 115 with phase -95.8 Test 10: freq = 2460.0 MHz Rx0/Tx0 xcorr peak at index 108 with phase -58.7 Rx0/Rx1 xcorr peak at index 115 with phase 12.9 >> On Thu, Mar 19, 2020 at 4:21 PM Lukas Haase <lukasha...@gmx.at> wrote: > Hi Rob, > > Yes, I confirm your conclusion. > > > - I calculate the relative phase by dividing the outputs of both > receivers. To understand better, note that I have an additional "IF stage" > in my own signal flow such that I exclude DC offset correction etc. the > USRP may perform. This is the block diagram of the transmitter part: > https://snipboard.io/YFgIKs.jpg . I send "exp(1j*1MHz*t) . This shows > the receiver part: https://snipboard.io/i9jLJg.jpg . I multiply the > received signal with exp(-1j*1MHz*t) and filter them. Then I divide both > streams and take the phase part. I take a moving average (for > flucatuations), add pi and display the number. > - https://snipboard.io/YFgIKs.jpg https://snipboard.io/YFgIKs.jpg > https://snipboard.io/YFgIKs.jpg That's so nice, thank you!! My code is > here: http://paste.ubuntu.com/p/MbCJfPGzYW/ . I'm not sure if you have > gnuradio(and QT) installed but if yes, simply "python2 switch_on_click.py" > should do. Let me quickly elaborate how it works: > - Class "switch_on_click" implements a normal gnuradio flow with > USRP transmitter and receiver. > - It also uses a custom module together with buttons and a probe > block to call functions upon clicking on a button > - The callback functions are defined in class "blk" > - The most important is "def button_rtx_handler" on line 106 which > is executed when user clicks on button "Switch RTX (together)" > - Again, thank you for trying this out!! If it works, would you mind > sharing this code then? I may be able to check then where it breaks on my > system > - I use 900 MHz as default center frequency (and "rf_freq"). When > clicking, I jump between dsp_freq=0 and dsp_freq=500e3. As to my waveform, > you can infer from my screenshots and code above: I am transmitting and > receiving a 1MHz waveform (which acts as an additional "IF stage"). The > received signal is then downconcerted from 1MHz to DC. I use 5 MSsps > sampling rate. > > > Again, thank you SO much. > > Best, > Lukas > > > *Gesendet:* Donnerstag, 19. März 2020 um 10:43 Uhr > *Von:* "Rob Kossler" <rkoss...@nd.edu> > *An:* "Lukas Haase" <lukasha...@gmx.at> > *Cc:* "USRP-users@lists.ettus.com" <usrp-users@lists.ettus.com> > *Betreff:* Re: [USRP-users] USRP X310 ignored DSP retuning on TX when > using a timed command > Hi Lukas, > So, the conclusion is that your Rx0-to-Rx1 relative phase is nearly > constant such that it seems that both Rx0/Rx1 are phase coherent and > Tx0/Tx1 are phase coherent. But, phase from Tx-to-Rx is random. Please > correct me if that is wrong. > > I have a few comments: > > - How do you measure/calculate the relative phase? > - Can you send me the full Python code to look at? As I mentioned > previously, I am not too good at gnuradio/Python, but I might be able to > spot something. > - As to your question, I always use synchronous measurements. And, > I'm confident that my Rx-to-Rx phase is coherent. But, I haven't really > looked at Tx-to-Rx in a while so I will do so later today. Here are the > steps I plan to take: > 1. Connect Tx0 to Rx1. Note that there is a pretty strong leakage > signal from Tx0 to Rx0 so I don't really need to provide a physical > connection in order to get a signal on Rx0. The signal attenuation in > this > leakage path is approx 40 dB so it is not too much different than the > signal level I will receive on Rx1 if I use an external 30 dB > attenuator. > 2. Set Rx and Tx frequency to freq 1 > 3. Measure and note the relative phase for Rx0/Tx0 and Rx1/Tx0 for > freq 1 > 4. Set Rx and Tx frequency to freq 2 > 5. Measure and note the relative phase for Rx0/Tx0 and Rx1/Tx0 for > freq 2 > 6. Repeat steps 2-5 a few times to ensure that the measurements are > repeatable > - Questions: what should I use for freq 1 and freq 2? What waveform > are you transmitting? What sample rates for Tx and Rx? > > Rob > > > > On Wed, Mar 18, 2020 at 7:47 PM Lukas Haase via USRP-users < > usrp-users@lists.ettus.com> wrote: > >> Hi Rob, >> >> I think the issue is really having two usrp_multi devices with timed >> commands and same timestmap or similar. From your tests below: >> >> 1.) I can *confirm *that the relative phase between two RX in your >> suggested test is always the same! In fact, it is always 4.56 rad, even >> across restarts and for different frequencies! That somewhat makes sense >> because the phase offset is now only dependent on the difference between >> the two channels (fixed) and cable lengths from the splitter (fixed). I >> verified by removing the timed command on usrp source, the phase offset >> becomes random after each retune. Of course, this is independent of TX >> tuning (timed vs. not). For reference, this is the code used: >> >> tune_req_rx = uhd.tune_request() >> tune_req_rx.rf_freq_policy = uhd.tune_request.POLICY_NONE >> tune_req_rx.dsp_freq_policy = uhd.tune_request.POLICY_MANUAL >> tune_req_rx.dsp_freq = -dsp_freq >> tune_req_tx = uhd.tune_request() >> tune_req_tx.rf_freq_policy = uhd.tune_request.POLICY_NONE >> tune_req_tx.dsp_freq_policy = uhd.tune_request.POLICY_MANUAL >> tune_req_tx.dsp_freq = dsp_freq >> >> now = usrp_sink.get_time_now() >> when = now + uhd.time_spec(1.0) >> >> usrp_sink.set_command_time(when) >> usrp_source.set_command_time(when) >> res1 = usrp_sink.set_center_freq(tune_req_tx) # TX >> res2 = usrp_source.set_center_freq(tune_req_rx, 0) #RX1 >> res3 = usrp_source.set_center_freq(tune_req_rx, 1) #RX2 >> usrp_sink.clear_command_time() >> usrp_source.clear_command_time() >> >> 2.) I also tried your second suggestion. Before reading on, you wanna >> guess what the outcome is? >> I connected "TX/RX" to "RX2" on UBX #1 (TX1 --> RX1) and "TX/RX" to "RX2" >> on UBX #2 (TX2 --> RX2). In absence of a second 30dB attenuator I used two >> antennas closely spaced together. For reference, my code looks now like: >> >> tune_req_rx = uhd.tune_request() >> tune_req_rx.rf_freq_policy = uhd.tune_request.POLICY_NONE >> tune_req_rx.dsp_freq_policy = uhd.tune_request.POLICY_MANUAL >> tune_req_rx.dsp_freq = -dsp_freq >> tune_req_tx = uhd.tune_request() >> tune_req_tx.rf_freq_policy = uhd.tune_request.POLICY_NONE >> tune_req_tx.dsp_freq_policy = uhd.tune_request.POLICY_MANUAL >> tune_req_tx.dsp_freq = dsp_freq >> >> now = usrp_sink.get_time_now() >> when = now + uhd.time_spec(1.0) >> >> usrp_sink.set_command_time(when) >> usrp_source.set_command_time(when) >> res1 = usrp_sink.set_center_freq(tune_req_tx, 0) # TX1 >> res2 = usrp_sink.set_center_freq(tune_req_tx, 1) # TX2 >> res3 = usrp_source.set_center_freq(tune_req_rx, 0) # RX1 >> res4 = usrp_source.set_center_freq(tune_req_rx, 1) # RX2 >> usrp_sink.clear_command_time() >> usrp_source.clear_command_time() >> >> I again look at the *relative phase* of RX1 and RX2 (obtained by >> dividing the two) and guess what: Also now the relative phase stays >> constant! (This time it actually slightly varies from 3.0 rad to 3.7 rad >> between two different frequencies). >> What does that mean? I think it means that TX must be tuned coherently >> and RX must be tuned coherently, i.e., timed commands generally work for >> multiple TX's and multiple RX's *individually*. Do I get that right? >> >> What doesn't seem to work is RX+TX *together*. >> >> I am very desperately asking if you had coherent TX+RX setup working at >> any point or know somebody who did. It would be so much worth to know if >> this is something that never worked to begin with or if I'm just doing >> something wrong. On the other hand I don't want to believe being the only >> person on the planet having tried TX+RX phase coherent operation :-/ >> >> Any other further suggestions on how to continue debugging with the above >> in mind would be helpful too. >> >> In my opinion there are two options left: >> 1.) There is still a nondeterministic delay between the TX and RX timed >> commands (to my understanding, even a constant delay would result in >> coherent phase) >> 2.) While the phase accumulators in RX are set to the same values (and in >> TX as well), they may be set to a different, random value. >> >> However, I don't really know how to test these. >> >> Thanks, >> Lukas >> >> >> *Gesendet:* Freitag, 13. März 2020 um 12:27 Uhr >> *Von:* "Rob Kossler" <rkoss...@nd.edu> >> *An:* "Lukas Haase" <lukasha...@gmx.at> >> *Cc:* "Marcus D Leech" <patchvonbr...@gmail.com>, " >> USRP-users@lists.ettus.com" <usrp-users@lists.ettus.com> >> *Betreff:* Re: [USRP-users] USRP X310 ignored DSP retuning on TX when >> using a timed command >> Ok, great. I am trying to think of ways to now add the phase >> measurement. Ideas... >> >> - In order to get consistent phase, you would need to tune Rx and Tx >> DSP at the same time (rather than below where you are only tuning one of >> them). So, assuming that this will not produce consistent phase results, >> then maybe try the following idea... >> - If you want to check just Rx DSP tuning (with fixed Tx DSP tuning), >> you could try a 2 channel Rx measurement where the Tx is split externally >> with 1:2 splitter in order to drive both Rx0 and Rx1. Then, measure the >> relative phase Rx0/Rx1 and then tune back and forth between two Rx DSP >> freqs to see if the relative phase on Rx remains constant. If so, this >> would give you good confidence that Rx DSP tuning is indeed happening >> synchronously >> - Assuming that the Rx IS synchronous in the step above (perhaps a >> bad assumption, but here goes), you could then check TX DSP tuning (with >> fixed Rx DSP tuning) by using two Tx and two Rx channels with Tx0 >> connected >> to Rx0 and Tx1 connected to Rx1. At this point we are confident that Rx >> DSP tuning is synchronous so any synchronous misbehavior would imply a Tx >> sync problem. >> >> Sorry I can't think of better ideas. >> Rob >> >> On Fri, Mar 13, 2020 at 12:12 PM Lukas Haase <lukasha...@gmx.at> wrote: >> >>> Hi Rob, >>> >>> 1.) yes, works(*) >>> 2.) yes, works(*) >>> >>> (*): qualitatively. I set the timed command to "get_current_time() + >>> uhd.time_spec(2.0)" and I see the chance 2 seconds after my click on the >>> screen. I cannot (do not know how) check if it actually happens at >>> sample-precicse location. >>> >>> Great, any ideas to simplify the setup would nice. I just don't know how >>> I could continue to debugging the phase. >>> >>> Best, >>> Luke >>> >>> >>> Gesendet: Freitag, 13. März 2020 um 11:08 Uhr >>> Von: "Rob Kossler" <rkoss...@nd.edu> >>> An: "Lukas Haase" <lukasha...@gmx.at> >>> Cc: "Marcus D Leech" <patchvonbr...@gmail.com>, " >>> USRP-users@lists.ettus.com" <usrp-users@lists.ettus.com> >>> Betreff: Re: [USRP-users] USRP X310 ignored DSP retuning on TX when >>> using a timed command >>> >>> Thanks Lukas, >>> I wanted to confirm that you did not have an older version of FPGA >>> firmware because there was a DDC/DUC bug fix[ >>> https://github.com/EttusResearch/fpga/commit/0b2364653405612a6d5dfaa0e69b1c6798771e6d] >>> related to phase. However, the version you provided with uhd_usrp_probe >>> confirms that you have the bug fix included. So, this is not the problem. >>> >>> From what you said, I assume that you can successfully do the following: >>> 1) with Rx tuning fixed (no re-tuning at all), tune Tx DSP only (do not >>> change TX RF) and you can see the frequency change at the specified command >>> time (i.e., if you specify the command time 1 sec in the future, the change >>> does not occur until 1 sec in the future). >>> 2) opposite of #1: with Tx tuning fixed, tune Rx DSP only and you can >>> see the frequency change at the specified command time. >>> >>> I am trying to simplify the issue by removing RF tuning completely and >>> by tuning only 1 of Rx/Tx at a time. Perhaps this will help lead to the >>> answer. >>> Rob >>> >>> >>> >>> On Fri, Mar 13, 2020 at 10:53 AM Lukas Haase <lukasha...@gmx.at[mailto: >>> lukasha...@gmx.at]> wrote:Hi again Rob, >>> >>> Yes, I confirm: >>> >>> 1.) Finally I get the commands to execute at the same time (TX and RX >>> individually and both at the same time) >>> 2.) Yes, the phase is random after each retune, even when I retune back >>> to the same frequency >>> 3.) (2) is only true if it includes *DSP* retuning. With naalog retuning >>> (+integer-N retuning) I get phase coherence, as expected. >>> >>> I actually expected the PLL retuning much more challenging than the DSP >>> retuning but for some reason it seems to be the opposite... >>> >>> Thanks, >>> Lukas >>> >>> >>> >> >> _______________________________________________ >> USRP-users mailing list >> USRP-users@lists.ettus.com >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > >
_______________________________________________ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
