USRP: Time and phase synchronization for source localization ??

[USRP]

Hello,

I used 2 USRP in Reception. They are connected between them via Mimo cable.

I want to localize transmitter source. So i need to synchronize the two receivers.

I did the constellation with the two USRP:

1-with identical cables         2-  with different cables.

(figure :attached files)

Have I synchronized my receivers (in time and  phase)?

please    help me

Best regards

[Anthony_F]

The MIMO cable with synchronize the USRPs frequency oscillator. There will still be some fixed phase offset between the two devices.

Can you explain more on "identical cables" and "different cables"

[USRP]

Identical cables: means that  the cables who connect each receiver to the transmitter have the same length.

Can I give to the two receivers the same phase offset to have two superposed signals when I use Identical cables?

Best regards

[USRP]

the two receivers with the transmitter:

[Anthony_F]

Thank you for the excellent picture.

The 10 MHz reference clock will ensure that all connected USRPs will remained locked in both frequency and phase, however it is still possible that the initial phase offset between USRPs is different.  I would suspect this is what you are seeing.

A quick reference into your communications book should show you that multiplying by e ^ (j * theta) can correct for these offsets. In LabVIEW this is easy with the Polar to Complex function. Take a quick look at this code snippet:

A MathScript version (which was mentioned in another thread) is contained here as well: https://decibel.ni.com/content/docs/DOC-19209

[USRP]

Thank you for your reponse.

I tried to mutplied the signal by exp(j*phaseOffset), but the problem is that the phase offset isn't constant !??

I did two measures: (phae offset isn't constant!)

this problem does not allow me to do localization: 

[ErikL]

The following example sends a calibration signal into the second input. Leakage between the two RX ports is used to detect and correct for the phase offset. From there MUSIC is used for position detection.

https://decibel.ni.com/content/docs/DOC-25716

[USRP]

Thank you for your reponse

Can you tell me if I can remplace the USRP REF TX by a generator to produce the calibration signal?

Best regards

[ErikL]

Yes. Any RF tone should work near the center frequency of the radio.

[USRP]

Thank you

I used RF generator that produced the calibration signal (near center frequency). But i have the same problem (phase offset not removed).

I have to add a code to remove phase offset?

Best regards