Power spectral density or meansquare spectrum estimate using periodogram method
Estimation / Power Spectrum Estimation
dspspect3
The Periodogram block estimates the power spectral density (PSD) or meansquare spectrum (MSS) of the input. It does so by using the periodogram method and Welch's averaged, modified periodogram method. The block averages the squared magnitude of the FFT computed over windowed sections of the input. It then normalizes the spectral average by the square of the sum of the window samples. See Periodogram (Signal Processing Toolbox) and Welch's Method (Signal Processing Toolbox) for more information.
The block treats MbyN framebased matrix input and MbyN samplebased matrix input as M sequential time samples from N independent channels. The block computes a separate estimate for each of the N independent channels and generates an N_{fft}byN matrix output.
Each column of the output matrix contains the estimate of the power spectral density of the corresponding input column at N_{fft} equally spaced frequency points. The frequency points are in the range [0,F_{s}), where F_{s} is the sampling frequency of the signal. The block always outputs samplebased data.
Specify the type of measurement for the
block to perform: Power spectral
density
or Meansquare
spectrum
. Tunable (Simulink).
Select the type of window to apply. See the Window Function block reference page for more details. Tunable (Simulink).
Enter the level, in decibels (dB), of
stopband attenuation, R_{s},
for the Chebyshev window. This parameter becomes
visible if, for the Window
parameter, you choose
Chebyshev
. Tunable (Simulink).
Enter the β parameter for the Kaiser window.
This parameter becomes visible if, for the
Window parameter, you chose
Kaiser
. Increasing
Beta widens the mainlobe and
decreases the amplitude of the sidelobes in the
displayed frequency magnitude response. Tunable (Simulink). See the
Window
Function block reference page for more
details.
From the list, choose
Symmetric
or
Periodic
. See the
Window
Function block reference page for more
details.Tunable (Simulink).
Set this parameter to
FFTW
to support an
arbitrary length input signal. The block restricts
generated code with FFTW implementation to
MATLAB^{®} host computers.
Set this parameter to
Radix2
for bitreversed
processing, fixed or floatingpoint data, or for
portable Ccode generation using the Simulink^{®} Coder™. The first dimension
M, of the input matrix must
be a power of two. To work with other input sizes,
use the Pad block
to pad or truncate these dimensions to powers of
two, or if possible choose the FFTW
implementation.
Set this parameter to
Auto
to let the block
choose the FFT implementation. For
nonpoweroftwo transform lengths, the block
restricts generated code to MATLAB host computers.
When you select this check box, the block uses the input frame size as the number of data points, N_{fft}, on which to perform the FFT. To specify the number of points on which to perform the FFT, clear the Inherit FFT length from estimation order check box. You can then specify a power of two FFT length using the FFT length parameter.
Enter the number of data points on which to perform the FFT, N_{fft}. When N_{fft} is larger than the input frame size, the block zeropads each frame as needed. When N_{fft} is smaller than the input frame size, the block wraps each frame as needed. This parameter becomes visible only when you clear the Inherit FFT length from input dimensions check box.
When you set the FFT
implementation parameter to
Radix2
, this value must be a
power of two.
Specify the number of spectra to average.
When you set this value to 1
,
the block computes the periodogram of the input.
When you set this value greater
1
, the block implements Welch's Method (Signal Processing Toolbox) to compute a modified
periodogram of the input.
If you select the Inherit sample time from input check box, the block computes the frequency data from the sample period of the input signal. For the block to produce valid output, the following conditions must hold:
The input to the block is the original signal, with no samples added or deleted (by insertion of zeros, for example).
The sample period of the timedomain signal in the simulation equals the sample period of the original time series.
If these conditions do not hold, clear the Inherit sample time from input check box. You can then specify a sample time using the Sample time of original time series parameter.
Specify the sample time of the original timedomain signal. This parameter becomes visible only when you clear the Inherit sample time from input check box.
Port  Supported Data Types 

Input 

Output 

[1] FFTW (http://www.fftw.org
)
[2] Frigo, M. and S. G. Johnson, “FFTW: An Adaptive Software Architecture for the FFT,”Proceedings of the International Conference on Acoustics, Speech, and Signal Processing, Vol. 3, 1998, pp. 13811384.
[3] Oppenheim, A. V. and R. W. Schafer. DiscreteTime Signal Processing. Englewood Cliffs, NJ: Prentice Hall, 1989.
[4] Orfanidis, S. J. Introduction to Signal Processing. Englewood Cliffs, NJ: PrenticeHall, 1995.
[5] Proakis, J. and D. Manolakis. Digital Signal Processing. 3rd ed. Englewood Cliffs, NJ: PrenticeHall, 1996.