Confidence intervals for PSD estimation

Display smoothed PSD estimation for the signal x1, compute:
a) for previously created signal with SNR=3 dB,
b) for modified mixture with SNR=10 dB,
c) for modified mixture with SNR=40 dB,
 4th checked result:
 Display smoothed PSD estimation and confidence intervals for the
significance level of 98%
for above mentioned 3 variants of signal x1, i.e. a mixtures of sinusionds and white noise with
SNR=3, 10 and 20 dB.
 Explain the reliability of PSD estimations for mentioned particular signals.
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