step
System object: phased.MatchedFilter
Package: phased
Perform matched filtering
Syntax
Y = step(H,X)
Y = step(H,X,COEFF)
[Y,GAIN] = step(___)
Description
Note
Starting in R2016b, instead of using the step method
to perform the operation defined by the System object™, you can
call the object with arguments, as if it were a function. For example, y
= step(obj,x) and y = obj(x) perform
equivalent operations.
Y = step(H,X) applies the matched filtering
to the input X and returns the filtered result
in Y. The filter is applied along the first dimension. Y and X have
the same dimensions. The initial transient is removed from the filtered
result.
The size of the first dimension of the input matrix can vary to simulate a changing signal length. A size change can occur, for example, in the case of a pulse waveform with variable pulse repetition frequency.
Y = step(H,X,COEFF) uses the input COEFF as
the matched filter coefficients. This syntax is available when you
set the CoefficientsSource property to 'Input
port'.
[Y,GAIN] = step(___) returns
additional output GAIN as the gain (in decibels)
of the matched filter. This syntax is available when you set the GainOutputPort property
to true.
Note
The object performs an initialization the first time the object is executed. This
initialization locks nontunable properties
and input specifications, such as dimensions, complexity, and data type of the input data.
If you change a nontunable property or an input specification, the System object issues an error. To change nontunable properties or inputs, you must first
call the release method to unlock the object.
Examples
Match Filter Linear FM Waveform
Construct a linear FM waveform with a sweep bandwidth of 300 kHz and a pulse width of 50 μs. Obtain the matched filter coefficients using the getMatchedFilter method. Then, use the step to match-filter the waveform.
waveform = phased.LinearFMWaveform('SweepBandwidth',3e5,... 'OutputFormat','Pulses','SampleRate',1e6,... 'PulseWidth',50e-6,'PRF',1e4); wav = waveform();
Plot the entire waveform. The length of the waveform is the pulse repetition interval (100 samples).
stem(real(wav)) xlabel('Samples') title('Real Part of Waveform')
Obtain the matched filter coefficients for the linear FM waveform. The length of the matched filter coefficients is the length of the pulse.
mfcoeffs = getMatchedFilter(waveform); stem(real(mfcoeffs)) xlabel('Samples') title('Real Part of Matched Filter Coefficients')
Use phased.MatchedFilter step method to obtain the matched filter output.
filter = phased.MatchedFilter('Coefficients',mfcoeffs); mfoutput = filter(wav); stem(real(mfoutput)) xlabel('Samples') title('Real Part of Matched Filter Output')
