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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.

    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.

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]

NumPhaseShifterBits

Number of phase shifter quantization bits

The number of bits used to quantize the phase shift component of beamformer or steering vector weights. Specify the number of bits as a non-negative integer. A value of zero indicates that no quantization is performed.

Default: 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

stepPerform MVDR beamforming
Common to All System Objects
clone

Create System object with same property values

getNumInputs

Expected number of inputs to a System object

getNumOutputs

Expected number of outputs of a System object

isLocked

Check locked states of a System object (logical)

release

Allow System object property value changes

Examples

expand all

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. The signal frequency is .01 hertz. The carrier frequency is 300 MHz.

t = [0:.1:200]';
fr = .01;
xm = sin(2*pi*fr*t);
c = physconst('LightSpeed');
fc = 300e6;
rng('default');
incidentAngle = [45;0];
array = phased.ULA('NumElements',5,'ElementSpacing',0.5);
x = collectPlaneWave(array,xm,incidentAngle,fc,c);
noise = 0.1*(randn(size(x)) + 1j*randn(size(x)));
rx = x + noise;

Compute the beamforming weights

beamformer = phased.MVDRBeamformer('SensorArray',array,...
    'PropagationSpeed',c,'OperatingFrequency',fc,...
    'Direction',incidentAngle,'WeightsOutputPort',true);
[y,w] = beamformer(rx);

Plot the signals

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

Plot the array response pattern using the MVDR weights

pattern(array,fc,[-180:180],0,'PropagationSpeed',c,...
    'Weights',w,'CoordinateSystem','rectangular',...
    'Type','powerdb');

References

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

Extended Capabilities

Introduced in R2012a

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