phased.MVDRBeamformer System object

Package: phased

Narrowband MVDR (Capon) beamformer

Description

The MVDRBeamformer object implements a minimum variance distortionless response beamformer. This is also referred to as a Capon beamformer.

To compute the beamformed signal:

  1. Define and set up your MVDR beamformer. See Construction.

  2. Call step to perform the beamforming operation according to the properties of phased.MVDRBeamformer. The behavior of step is specific to each object in the toolbox.

Construction

H = phased.MVDRBeamformer creates a minimum variance distortionless response (MVDR) beamformer System object™, H. The object performs MVDR beamforming on the received signal.

H = phased.MVDRBeamformer(Name,Value) creates an MVDR beamformer object, H, with each specified property Name set to the specified Value. You can specify additional name-value pair arguments in any order as (Name1,Value1,...,NameN,ValueN).

Properties

SensorArray

Sensor array

Sensor array specified as an array System object belonging to the phased package. A sensor array can contain subarrays.

Default: phased.ULA with default property values

PropagationSpeed

Signal propagation speed

Specify the propagation speed of the signal, in meters per second, as a positive scalar.

Default: Speed of light

OperatingFrequency

System operating frequency

Specify the operating frequency of the beamformer in hertz as a positive scalar. The default value corresponds to 300 MHz.

Default: 3e8

DiagonalLoadingFactor

Diagonal loading factor

Specify the diagonal loading factor as a positive scalar. Diagonal loading is a technique used to achieve robust beamforming performance, especially when the sample support is small. This property is tunable.

Default: 0

TrainingInputPort

Add input to specify training data

To specify additional training data, set this property to true and use the corresponding input argument when you invoke step. To use the input signal as the training data, set this property to false.

Default: false

DirectionSource

Source of beamforming direction

Specify whether the beamforming direction for the beamformer comes from the Direction property of this object or from an input argument in step. Values of this property are:

'Property'The Direction property of this object specifies the beamforming direction.
'Input port'An input argument in each invocation of step specifies the beamforming direction.

Default: 'Property'

Direction

Beamforming directions

Specify the beamforming directions of the beamformer as a two-row matrix. Each column of the matrix 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. This property applies when you set the DirectionSource property to 'Property'.

Default: [0; 0]

WeightsOutputPort

Output beamforming weights

To obtain the weights used in the beamformer, set this property to true and use the corresponding output argument when invoking step. If you do not want to obtain the weights, set this property to false.

Default: false

Methods

cloneCreate MVDR beamformer object with same property values
getNumInputsNumber of expected inputs to step method
getNumOutputsNumber of outputs from step method
isLockedLocked status for input attributes and nontunable properties
releaseAllow property value and input characteristics changes
stepPerform MVDR beamforming

Examples

Apply an MVDR beamformer to a 5-element ULA. The incident angle of the signal is 45 degrees in azimuth and 0 degree in elevation.

% Signal simulation
t = (0:1000)';
x = sin(2*pi*0.01*t);
c = 3e8; Fc = 3e8;
incidentAngle = [45; 0];
ha = phased.ULA('NumElements',5);
x = collectPlaneWave(ha,x,incidentAngle,Fc,c);
noise = 0.1*(randn(size(x)) + 1j*randn(size(x)));
rx = x+noise;

% Beamforming
hbf = phased.MVDRBeamformer('SensorArray',ha,...
    'PropagationSpeed',c,'OperatingFrequency',Fc,...
    'Direction',incidentAngle,'WeightsOutputPort',true);
[y,w] = step(hbf,rx);

% Plot signals
plot(t,real(rx(:,3)),'r:',t,real(y));
xlabel('Time'); ylabel('Amplitude');
legend('Original','Beamformed');

% Plot response pattern
figure;
plotResponse(ha,Fc,c,'Weights',w);

References

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

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