UHD2: IQ Collection

This page is still under development and the experiment described on this page is not yet generally available.

1) Experiment Overview

Experiment Definition: This experiment collects IQ samples from USRP and saves the results in a mat file for post-processing.

Experiment Goals: The IQ samples are collected at multiple center frequencies with some sampling rate for a specified amount of duration. The experimenter can then specify a wait duration after which another batch of IQ samples is collected. This can be repeated for the duration of the experiment. IQ samples are saved as mat files under /root/Results. A use case may be that a fixed node can be configured as eNB to transmit LTE signal and the portable can run IQ collection on a portable node to see the variation of LTE signal as the portable node follows a trajectory.       

Experiment Modes: This experiment is available in both EMULATION and TESTBED modes. However, to run this experiment in the EMULATION mode, you will need to couple this experiment with one of the other sample experiments to introduce a signal source, e.g. with SE1 sample experiment to introduce an LTE eNB.  

Configuration Parameters:

• USRP RX gain 

• USRP sampling rate

• Center frequencies

• Duration of IQ waveform

• Wait time between each IQ collection

• Experiment duration

2) Performing the Experiment:

Login to the E-VM and navigate to the folder containing all the Radio scripts 

$ cd /root/Profiles/ProfileScripts/Radio 

Copy the spectrum monitoring script as startRadio.sh

$ cp Samples/startIQCollection.sh startRadio.sh 

Use an editor to uncomment the line  /Radio/startRadio.sh in /root/startexperiment.sh and run the following command:

$ /root/startexperiment.sh  

3) Modifying the Experiment Configuration Parameters:

The python file located at the  /root/Profiles/SDR_control/LTE_IQ/myConstants.py can be edited to modify the parameters in the experiment

USRP RX gain (default value:40)

gainRX = (40,) 

USRP sampling rate (default value: 2 MHz)

fs = 2e6 

Center frequencies (default value:3500 MHz and 3510 MHz). One can specify as many center frequencies as needed.

fLO = (3500e6, 3510e6)

Duration of IQ waveform in ms (default value:20 ms)

IQ_duration = 20 

Wait time between each IQ collection in ms (default value:77 ms)

wait_duration = 77 

Experiment duration in seconds (default value: 0.5 seconds)

total_duration = 0.5 

4) Results:

The mat files that contain IQ samples can be loaded in MATLAB for post-processing. The experiment also creates a log file under /root/Results. For an example on post-processing the IQ samples based on LTE recordings, see the following user manual page under Section 4.1.4: https://sites.google.com/ncsu.edu/aerpaw-wiki/aerpaw-user-manual/4-sample-experiments-repository/4-1-radio-software/4-1-4-uhd-python-api-experiments/lte-iq-post-processing