Spectrum Analysis of Signals
This example shows downstream spectrum analysis of signals using MATLAB®, Communications Toolbox™ and DSP System Toolbox™. You can either use captured signals, or receive signals in real time using the RTL-SDR Radio, ADALM-PLUTO Radio or USRP™ Radio. You can change the radio's center frequency to tune the radio to a band where a signal is present. You can then use the spectrum analyzer to view and make measurements on the received spectrum.
For Simulink® implementation of this example, refer Spectrum Analysis of Signals in Simulink.
Required Hardware and Software
To run this example using captured signals, you need the following software:
To receive signals in real time, you also need one of the following hardware:
RTL-SDR radio and the corresponding software Communications Toolbox Support Package for RTL-SDR Radio
ADALM-PLUTO radio and the corresponding software Communications Toolbox Support Package for ADALM-PLUTO Radio
USRP radio and the corresponding software Communications Toolbox Support Package for USRP Radio
For a full list of Communications Toolbox supported SDR platforms, refer to the "MATLAB and Simulink Hardware Support for SDR" section of Software-Defined Radio (SDR).
The receiver asks for user input and initializes variables. Then, it calls the signal source and FM broadcast receiver in a loop. The loop also keeps track of the radio time using the frame duration and lost samples reported by the signal source.
For the option to change default settings, set |cmdlineInput| to 1.
cmdlineInput = false; if cmdlineInput % Request user input from the command-line for application parameters userInput = helperSpectralAnalysisUserInput; % Set initial parameters [SAParams, sigSrc] = helperSpectralAnalysisConfig(userInput); else % Set initial parameters load defaultInputSpecAnalysis.mat [SAParams, sigSrc] = helperSpectralAnalysisConfig; end
spectrumAnalyzer object and configure based on user input
hSpectrum = spectrumAnalyzer(... 'Name', 'Passband Spectrum',... 'Title', 'Passband Spectrum', ... 'Method', 'Welch', ... 'SpectrumType', 'Power density', ... 'FrequencySpan', 'Full', ... 'SampleRate', SAParams.FrontEndSampleRate, ... 'SpectralAverages', 50, ... 'FrequencyOffset', SAParams.CenterFrequency, ... 'YLimits', [-120 10], ... 'YLabel', 'Magnitude-squared, dB', ... 'Position', figposition([50 30 30 40]));
View the spectrum. While the spectrum analyzer is running, you can measure peaks, occupied bandwidth, and other properties of the signal.
% Initialize radio time radioTime = 0; % Main loop while radioTime < userInput.Duration % Receive baseband samples (Signal Source) if SAParams.isSourceRadio if SAParams.isSourcePlutoSDR rcv = sigSrc(); lost = 0; late = 1; elseif SAParams.isSourceUsrpRadio rcv= sigSrc(); lost = 0; else [rcv,~,lost,late] = sigSrc(); end else rcv = sigSrc(); lost = 0; late = 1; end rcv = rcv - mean(rcv); % Remove DC component. step(hSpectrum, rcv); % Update radio time. If there were lost samples, add those too. radioTime = radioTime + SAParams.FrontEndFrameTime + ... double(lost)/SAParams.FrontEndSampleRate; end % Release all System objects release(sigSrc); release(hSpectrum);
In this example, you used Communications Toolbox™ System objects to analyze the spectrum of a received signal.