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step

System object: phased.SubbandPhaseShiftBeamformer
Package: phased

Beamforming using subband phase shifting

Syntax

Y = step(H,X)
Y = step(H,X,ANG)
[Y,W] = step(___)
[Y,FREQ] = step(___)
[Y,W,FREQ] = step(___)

Description

Y = step(H,X) performs subband phase shift beamforming on the input, X, and returns the beamformed output in Y.

Y = step(H,X,ANG) uses ANG as the beamforming direction. This syntax is available when you set the DirectionSource property to 'Input port'.

[Y,W] = step(___) returns the beamforming weights, W. This syntax is available when you set the WeightsOutputPort property to true.

[Y,FREQ] = step(___) returns the center frequencies of subbands, FREQ. This syntax is available when you set the SubbandsOutputPort property to true.

[Y,W,FREQ] = step(___) returns beamforming weights and center frequencies of subbands. This syntax is available when you set the WeightsOutputPort property to true and set the SubbandsOutputPort property to true.

    Note:   The object performs an initialization the first time the step method 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.

Input Arguments

H

Beamformer object.

X

Input signal, specified as an M-by-N matrix. If the sensor array contains subarrays, N is the number of subarrays; otherwise, N is the number of elements.

ANG

Beamforming directions, specified as a two-row matrix. Each column has the form [AzimuthAngle; ElevationAngle], in degrees. Each azimuth angle must be between –180 and 180 degrees, and each elevation angle must be between –90 and 90 degrees.

Output Arguments

Y

Beamformed output. Y is an M-by-L matrix, where M is the number of rows of X and L is the number of beamforming directions.

W

Beamforming weights. W has dimensions N-by-K-by-L. K is the number of subbands in the NumSubbands property. L is the number of beamforming directions. If the sensor array contains subarrays, N is the number of subarrays; otherwise, N is the number of elements. Each column of W specifies the narrowband beamforming weights used in the corresponding subband for the corresponding direction.

FREQ

Center frequencies of subbands. FREQ is a column vector of length K, where K is the number of subbands in the NumSubbands property.

Examples

Apply subband phase shift beamformer to an 11-element ULA. The incident angle of the signal is 10 degrees in azimuth and 30 degrees in elevation.

% Signal simulation
ha = phased.ULA('NumElements',11,'ElementSpacing',0.3);
ha.Element.FrequencyRange = [20 20000];
fs = 1e3; carrierFreq = 2e3; t = (0:1/fs:2)';
x = chirp(t,0,2,fs);
c = 1500; % Wave propagation speed (m/s)
hc = phased.WidebandCollector('Sensor',ha,...
    'PropagationSpeed',c,'SampleRate',fs,...
    'ModulatedInput',true,'CarrierFrequency',carrierFreq);
incidentAngle = [10; 30];
x = step(hc,x,incidentAngle);
noise = 0.3*(randn(size(x)) + 1j*randn(size(x)));
rx = x+noise;

% Beamforming
hbf = phased.SubbandPhaseShiftBeamformer('SensorArray',ha,...
    'Direction',incidentAngle,...
    'OperatingFrequency',carrierFreq,'PropagationSpeed',c,...
    'SampleRate',fs,'SubbandsOutputPort',true,...
    'WeightsOutputPort',true);
[y,w,subbandfreq] = step(hbf,rx);

Algorithms

The subband phase shift beamformer separates the signal into several subbands and applies narrowband phase shift beamforming to the signal in each subband. The beamformed signals in all the subbands are regrouped to form the output signal.

For further details, see [1].

References

[1] Van Trees, H. Optimum Array Processing. New York: Wiley-Interscience, 2002.

See Also

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