Capture Over-The-Air Signals

You can use the Communications Toolbox™ Support Package for USRP®[1] Embedded Series Radio together with a supported SDR device to capture over-the-air signals to the MATLAB® workspace.

Capture RF Data to Baseband File Using E3xx Radio Hardware

Use the capture function to record RF signals for post-capture processing in MATLAB®. Save an FM broadcast signal to a file as baseband samples. Read the file containing the recorded signal and demodulate the baseband samples.

Configure SDR Hardware

If your radio hardware is already configured for host-radio communication, you can skip this section. To configure your radio hardware for host-radio communication, follow the steps in the Guided Host-Radio Hardware Setup. Attach an antenna suitable for the 88-108 MHz band to the first RX channel.

Configure Receiver System Object

Create a receiver System object with the specified properties. The specified center frequency corresponds to a local FM station.

stationCenterFrequency = 95e6;
deviceName = 'E3xx';
rx = sdrrx(deviceName,'BasebandSampleRate',528e3,...
    'CenterFrequency',stationCenterFrequency,'OutputDataType','Double');

Initiate Data Capture to File

Call the capture function, specifying the receiver object, capture duration, and file name. The function returns the captured data in a file named "FMRecording.bb". After capturing the FM signal, unlock the receiver object using the release function.

capture(rx,5,'Seconds','Filename','FMRecording.bb');
## Establishing connection to hardware. This process can take several seconds.
release(rx);

Demodulate FM Recording

Create a comm.BasebandFileReader System object to read the captured signal and extract frames of data from the file. Set baseband file reader to take 4400 samples per frame when reading the saved baseband signal.

bbr = comm.BasebandFileReader('FMRecording.bb');
bbr.SamplesPerFrame = 4400;

Use the BasebandSampleRate field of the baseband file reader object to set the SampleRate property of the demodulator. Find the BasebandSampleRate field in the MetaData structure. Create a comm.FMBroadcastDemodulator System object. Demodulate and play back each frame of the FM data. Use a while loop to read all frames of the captured data.

fmbDemod = comm.FMBroadcastDemodulator( ...
    'AudioSampleRate', 48e3, ...
    'SampleRate',bbr.Metadata.BasebandSampleRate,'PlaySound',true);

while ~isDone(bbr)
    fmbDemod(bbr());
end

See Also

Functions

See Also

Objects


[1] USRP, USRP2, UHD, and Ettus Research are trademarks of National Instruments Corp.