Can spectrumAnalyzer show the power level of complex I&Q signal?

I created a complex linear frequency modulated Chirp signal (constant envelop) anad complex noise. When I use spectrumAnalyzer within the MATLAB live script, it shows non-constant spectrum. Is there a way to show complex signal's power and noise?

% For repeatable simulations, set the random number generator to default
rng default;
noisesigI = wgn(numSamples,1,10*log10(N))';
noisesigQ = wgn(numSamples,1,10*log10(N))';
noisesig = 1/(sqrt(2))*complex(noisesigI,noisesigQ);
rxwaveform = (scaledsig + noisesig);

% Scale the received signal for having unit power
Scaled_rxwaveform = rxwaveform/rms(rxwaveform);
ShowVisualizations =1;
if ShowVisualizations == 1
    rxscope = spectrumAnalyzer(SampleRate = baseFs, ...
        PlotAsTwoSidedSpectrum = true, ...
        SpectrumType = "Power", ...
        SpectrumUnits = "dBW", ...
        Title = "Received signal BB UDC + Noise spectrum");
    rxscope(rxwaveform', noisesig',scaledsig');  %scope accepts only column vec.
end

Answer 1

[Alan]

Hi Taehwan,

It looks like you are expecting only the noise signal’s spectrum. The figure you have shown has 3 spectrums which are the original signal, noise signal, and the signal with noise. That is because you have called rxscope on all 3 signals together.

If you aim to view the signals separately, call different instances of spectrumAnalyzer on each signal separately:

rxscope = spectrumAnalyzer('SampleRate', fs, ...

'PlotAsTwoSidedSpectrum', true, ...

'SpectrumType', "Power", ...

'SpectrumUnits', "dBW", ...

'Title', "Resultant Signal");

rxscope(rxwaveform'); % Resultant signal with noise

rxscope2 = spectrumAnalyzer('SampleRate', fs, ...

'PlotAsTwoSidedSpectrum', true, ...

'SpectrumType', "Power", ...

'SpectrumUnits', "dBW", ...

'Title', "Noise Signal");

rxscope2(noisesig'); % Noise signal

For more information on spectrumAnalyzer you can check out:

https://www.mathworks.com/help/releases/R2023b/dsp/ref/spectrumanalyzer.html

I hope this helps.