Save Captured Signal with Metadata to Baseband File

Since R2023a

This example shows how to configure a software-defined radio (SDR) as a baseband receiver to capture a signal from the air. The example then shows how to save to a baseband file with metadata that includes global positioning system disciplined oscillator (GPSDO) data and a custom label.

Set Up Radio

Call the radioConfigurations function. The function returns all available radio setup configurations that you saved using the Radio Setup wizard.

savedRadioConfigurations = radioConfigurations;

To update the dropdown menu with your saved radio setup configuration names, click Update. Then select the radio to use with this example.

savedRadioConfigurationNames = [string({savedRadioConfigurations.Name})];
radio = savedRadioConfigurationNames(1) ;

Use the radioConfigurations function with the configuration name to create a radio object.

rc = radioConfigurations(radio);

Configure Baseband Receiver

Create a basebandReceiver object with the specified radio. Because the object requires exclusive access to radio hardware resources, before running this example for the first time, clear any other object associated with the specified radio. In subsequent runs, to speed up the execution time of the example, reuse your new workspace object.

if ~exist("bbrx","var")
    bbrx = basebandReceiver(radio);
end

Set the baseband receiver object properties. To use the maximum sample rate available for your radio, call the hMaxSampleRate helper function. Alternatively, you can set a custom sample rate.

maxSampleRate = hMaxSampleRate(radio);
bbrx.SampleRate =  maxSampleRate;
bbrx.CenterFrequency = 2450000000;
bbrx.RadioGain = 30;

To update the dropdown menu with the antennas available for your radio, call the hCaptureAntennas helper function. Then select the antenna to use with this example.

antennaSelection = hCaptureAntennas(radio);
bbrx.Antennas = antennaSelection(2);

Capture Signal

To capture a signal, call the capture function on the baseband receiver object. Specify the length of the capture.

[data,timestamp] = capture(bbrx,milliseconds(100));

Get GPS NMEA Sentence

If your radio has a GPSDO sensor, use the radio object to get the National Marine Electronics Association (NMEA) sentence.

% Select the check box if your radio has a GPSDO
hasGPSDO = false;

if hasGPSDO
    sentence = getGPSNMEA(rc);
else
    sentence = "No GPSDO available";    
end

Create Metadata

Create a metadata structure that includes the NMEA sentence and a custom text label.

metadata.Timestamp = char(timestamp);
metadata.Antennas = char(bbrx.Antennas);
metadata.RadioConfiguration = char(radio);
metadata.NMEAGGASentence = char(sentence);
metadata.CustomLabel = 'Data from capture example';

Save Signal and Metadata to Baseband File

Call the comm.BasebandFileWriter System object™ to write the captured signal to a baseband file with the metadata. To read the content of the baseband file, you can use the comm.BasebandFileReader System object.

bbw = comm.BasebandFileWriter;
bbw.Filename = 'captured_data.bb';
bbw.SampleRate = bbrx.SampleRate;
bbw.CenterFrequency = bbrx.CenterFrequency;
bbw.Metadata = metadata;
bbw(data);