Synchro to external 1pps in PN generation and correlation

[Piero_AQ]

I am trying to use a USP NI 2920, under Labview control, in order to make a sort of channel sounding.  The USRP generates a pseudonoise (PN) sequence that BPSK modulate the carrier sent to a TX antenna.  The same USRP runs a receiver process that acquire the signal form RX antenna, demodulate it and correlate it with a copy of the PN.  Both TX sequence and RX acquisition must be synchronized to the 1PPS input signal. This because I want to use another USRP located in a different place but sharing the same 1PPS and 10 MHz with the first USRP.

Can I do that from Labview?  Is there any example or tutorial from which I can get some suggestions? Are there any limitations in time accuracy? I need a time resolution of 1 sample (e.g. 50 ns @ 20 MHz sampling rate) both at TX and RX.

Thank you in advance.

Best regards

Piero

[kimera]

Hi Piero,

looks about these examples:

NI USRP Example LabVIEW VIs

https://decibel.ni.com/content/groups/ni-usrp-example-labview-vis?view=documents

Regards,

A.

[ErikL]

Hello!

You have two options:

1. Cabled

See the MIMO tutorial.  It has a brief discussion on synchronizing multiple USRPs.  http://www.ni.com/white-paper/14311/en

2. GPSDO.

The USRP-293x integrate a GPS and OCXO for distributed synchronization.  Ideally this is down to 50nS but should be at least a sample in practice.  Frequency accuracy will also be better which is important for channel sounding.

[Piero_AQ]

Hello ErikL,

thank you for your suggestions.  From those it seems that using a single USRP don't allow to synchronize TX and RX processes within the same USRP. Does it?

Another question: if I use two USRP with 1pps & 10 MHz distribuited from a common source, can I avoid to use the MIMO cable?

Thank you in advance

Piero

[Piero_AQ]

Is there any specific example you suggest to start from?

Best regards

Piero

[ErikL]

You can syncrhonize TX/RX on the same USRP using timed commands.  You can use the same approach on a single or any number of USRP so long as they share the time reference.

Yes, externally abling PPS and Ref has the same effect as the MIMO cable.  The MIMO cable is only for convenience.

The following example explains timed commands:

niUSRP EX Rx Multiple Synchronized Inputs.vi

niUSRP EX Tx Multiple Synchronized Outputs.vi

On my computer examples can be found in the folder:

C:\Program Files (x86)\National Instruments\LabVIEW 2011\examples\instr\niUSRP