Hello everyone working with the USRP,
I share my experience for setting live all the parameters of a QAM transmission between 2 USRP (2920 or 2932). We will use these VIs to train our students in the basics of digital radio transmissions.
As I am a new participant in this forum, I do not know if I can transmit my complete Labview project, so I am already publishing the operating principle and views of the 2 VIs.
I relied on the National Instruments examples, "niUSRP EX QAM Tx.vi" and "niUSRP EX QAM Rx.vi".
The idea was to be able to modify all the settings without having to stop and restart the VIs.
The most sensitive setting is the modification of the IQ sampling rate: I used a case selection to briefly stop the USRP session and restart it with the new sampling rate value.
I also noticed some problems:
- The Gaussian mode for the filter is seemingly not supported for QAM modulation. So I deleted this choice in the "TX and RX" Filter controls.
- USRP 2920 and 2932 seem to have problems with RX operation when the Carrier Frequency is not a value ending in 0 or 5. I have set the "step" of these controls in steps of 5 MHz. This problem still needs to be deepened, because I did not have time to do more precise tests to determine why the RX frequency does not work with a finer step.
I look forward to receiving feedback!
P.S.:
- my development is done in LabVIEW 2017, with Modulation Toolkit v18.0 and NI-USRP v17.1.
