Table Of Contents

Synchronizing with the NI-USRP Driver

Last Modified: July 10, 2019

Complete the following steps to configure and synchronize the MIMO system:

  1. Open the receive (RX) session by specifying the IP address of each USRP device. Separate each IP address with a comma.
  2. Set the Start Trigger Time, in seconds and fractional seconds, to indicate when all USRP devices should begin fetching data.
  3. Set the inputs and outputs shared by all eight devices.
  4. Specify which devices use the external reference or MIMO cable.
  5. Use niUSRP Set Time to set the time of the onboard device timer. Set this time to be earlier than the Start Trigger Time you set in step 2. Set the onboard device timer according to your device configuration.
    • If the device uses an external PPS signal (PPS In or GPS), set apply timestamp to Next Timebase Edge.
    • If the device uses a PPS signal from the MIMO connector, do not call niUSRP Set Time. The onboard device timer automatically synchronizes to the master device and drives the timestamp over the MIMO connector.
    • If the device does not use an external PPS signal (Internal), set apply timestamp to Now.
    spd-note-note
    Note  

    The channel list specifies which devices to set to 0. Set the channel list input to a list of comma-separated string values such as "dev0, dev1" to denote the devices you want niUSRP Set Time on.

  6. Fetch the data using a single driver call, returned as a 2D array of complex samples where each row contains the complex in-phase/quadrature (I/Q) waveform from a single antenna.
  7. Repeat steps 1 through 6, replacing RX with TX to configure a transmit (TX) session.

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