- Measure & Report phase alignment and phase stability of USRPs
 - Wire diagram: 

    ______________       ______________ 
   |              |     |              |
   |    USRP 1    |     |    USRP 2    |
   |______________|     |______________|
     ^ |______^ |_________^  | 
     |_______________________|

    - USRP 1: send tone from first to second daughterboard - delta_phi_1
    - USRP 1: send tone from second daughterboard to USPR 2 - delta_phi_2
    - USRP 2: send tone to first daughterboard (USRP1) - delta_phi_3
    
    Arbitrary number of RX-USRPs and TX-USRPs possible.

    test_signal = sin(2*pi*f*t + phi)
    reference = sin(2*pi*f*t)