Multi USRP Phased Array System

Dear all,

First of all I’m going to explain our problem: We are trying to build a
multi USRP system.

HW: 8 N210 ETTUS boards with WBS daughterboards. We’ve got a 10Mhz/1PPS
signal generator and distribution system for 8 channels.

Purpose: Our purpose is to capture the 8 channels coherently (we got
this thanks to the signal distribution system) and aligned (phase and
time the same for all the channels).

Problems:

  1. We started experimenting problems with the relative phase difference
    among the channels of our system. We have read through the forum that
    the WBS locks at a aleatory phase each time it’s tunned. We haven’t
    found any kind of solution to this problem directly solved by the uhd SW

  2. In order to solve the problem of the aleatorious phase we have
    thought to do the sampling in two steps, the first step would be a
    limited amount of data adquisition (100 ms), switching on a coupler, to
    inject a known reference signal (let’s say a tone), in order to stimate
    the Cross correlation by pairs of channels so that we could calculate
    the relative delay of each channel with a reference channel. Once done
    that we swithched off the coupler so we could start the sampling (no
    retunne, only stream command), but the problem is still there, altought
    no retune is done again a new phase (different from the first one) is
    observed.

We have gotten to a let’s say frustrating point and we don’t have much
more ideas to go ahead (we already know that with the MIMO it’s solved)
so we would really appreciate any input to give us any light to our
problem.

If you need the code or any other input, please let me know.

Thanks in advance and kind regards,

Javier

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