Delay of NI USRP 2943R is too large

[aschwind]

Hey everyone,

I'm working on LabVIEW 2016 and NI USRP 2943R (via Ethernet 1G or PCIe-8371)

By the attached VI, the technical delay between incoming signal on RX2 and outgoing signal on TX1 has to been measured.

I expected a delay around 10-20ms, but I got about 80ms(IQ rate 500k) and 55ms (IQ rate 4M) by using Ethernet 1Gbit/s and I also got the same values by using PCIe.

1) Why is the delay larger at small IQ rate than big IQ rate?

2) Why is the delay so large? The USRP should be used for Rx/Tx LTE signals (BW 20MHz+). Can I improve these values by optimizing the VI?

3) Why is there no big difference between connection via Ethernet 1G and PCIe?

Here is my system:

Win7 (CPU: i7), LabVIEW 2016 (32bit), Realtek NIC (1G), NI USRP 2943R

Thanks, Andreas.

[Christoph_D]

Hi Andreas,

I didnt run your Vi and havent measured the times myself, but I try to answer your question anyway:

1. If you have a smaller IQ rate it should take longer to acquire a certain number of samples. You require a certain number of samples to be acquired and you get the samples after all samples have been acquired, so the delay is (also) caused by the time between the first and last sample. And that time is smaller for faster acquisitions
2. If you really improve that drastically you should make use of the user accessible FPGA of your 2943R then it would rather be a matter of ns to us. If you stream the data to the host application and back it just takes a while to do that and additional time for the host computer to process the request.
3. I would guess that the delay is dominantly caused by the host application and is not due to the connection or bandwith of the connection. As mentioned in (2) please make use of the FPGA for low latency I/O.

Best regards,

Christoph