# sensorsig

Simulate received signal at sensor array

## Syntax

## Description

simulates
the received narrowband plane wave signals at a sensor array. `x`

= sensorsig(`pos`

,`ns`

,`ang`

)`pos`

represents
the positions of the array elements, each of which is assumed to be
isotropic. `ns`

indicates the number of snapshots
of the simulated signal. `ang`

represents the incoming
directions of each plane wave signal. The plane wave signals are assumed
to be constant-modulus signals with random phases.

## Examples

### Received Signal and Direction-of-Arrival Estimation

Simulate the received signal at an array, and use the data to estimate the arrival directions.

**Note:** This example runs only in R2016b or later. If you are using an earlier release, replace each call to the function with the equivalent `step`

syntax. For example, replace `myObject(x)`

with `step(myObject,x)`

.

Create an 8-element uniform linear array whose elements are spaced half a wavelength apart.

fc = 3e8; c = 3e8; lambda = c/fc; array = phased.ULA(8,lambda/2);

Simulate 100 snapshots of the received signal at the array. Assume there are two signals, coming from azimuth 30° and 60°, respectively. The noise is white across all array elements, and the SNR is 10 dB.

```
x = sensorsig(getElementPosition(array)/lambda,...
100,[30 60],db2pow(-10));
```

Use a beamscan spatial spectrum estimator to estimate the arrival directions, based on the simulated data.

estimator = phased.BeamscanEstimator('SensorArray',array,... 'PropagationSpeed',c,'OperatingFrequency',fc,... 'DOAOutputPort',true,'NumSignals',2); [~,ang_est] = estimator(x);

Plot the spatial spectrum resulting from the estimation process.

plotSpectrum(estimator)

The plot shows peaks at 30° and 60°.

### Signals With Different Power Levels

Simulate receiving two uncorrelated incoming signals that have different power levels. A vector named `scov`

stores the power levels.

Create an 8-element uniform linear array whose elements are spaced half a wavelength apart.

fc = 3e8; c = 3e8; lambda = c/fc; ha = phased.ULA(8,lambda/2);

Simulate 100 snapshots of the received signal at the array. Assume that one incoming signal originates from 30 degrees azimuth and has a power of 3 W. A second incoming signal originates from 60 degrees azimuth and has a power of 1 W. The two signals are not correlated with each other. The noise is white across all array elements, and the SNR is 10 dB.

```
ang = [30 60];
scov = [3 1];
x = sensorsig(getElementPosition(ha)/lambda,...
100,ang,db2pow(-10),scov);
```

Use a beamscan spatial spectrum estimator to estimate the arrival directions, based on the simulated data.

hdoa = phased.BeamscanEstimator('SensorArray',ha,... 'PropagationSpeed',c,'OperatingFrequency',fc,... 'DOAOutputPort',true,'NumSignals',2); [~,ang_est] = step(hdoa,x);

Plot the spatial spectrum resulting from the estimation process.

plotSpectrum(hdoa);

The plot shows a high peak at 30 degrees and a lower peak at 60 degrees.

### Reception of Correlated Signals

Simulate the reception of three signals, two of which are correlated.

Create a signal covariance matrix in which the first and third of three signals are correlated with each other.

scov = [1 0 0.6;... 0 2 0;... 0.6 0 1];

Simulate receiving 100 snapshots of three incoming signals from 30°, 40°, and 60° azimuth, respectively. The array that receives the signals is an 8-element uniform linear array whose elements are spaced one-half wavelength apart. The noise is white across all array elements, and the SNR is 10 dB.

pos = (0:7)*0.5; ns = 100; ang = [30 40 60]; ncov = db2pow(-10); x = sensorsig(pos,ns,ang,ncov,scov);

### Theoretical and Empirical Covariance of Received Signal

Simulate receiving a signal at a URA. Compare the signal theoretical covariance with its sample covariance.

Create a 2-by-2 uniform rectangular array having elements spaced 1/4-wavelength apart.

pos = 0.25 * [0 0 0 0; -1 1 -1 1; -1 -1 1 1];

Define the noise power independently for each of the four array elements. Each entry in `ncov`

is the noise power of an array element. This element position is the corresponding column in `pos`

. Assume the noise is uncorrelated across elements.

ncov = db2pow([-9 -10 -10 -11]);

Simulate 100 snapshots of the received signal at the array, and store the theoretical and empirical covariance matrices. Assume that one incoming signal originates from 30° azimuth and 10° elevation. A second incoming signal originates from 50° azimuth and 0° elevation. The signals have a power of 1 W and are uncorrelated.

```
ns = 100;
ang1 = [30; 10];
ang2 = [50; 0];
ang = [ang1, ang2];
rng default
[x,rt,r] = sensorsig(pos,ns,ang,ncov);
```

View the magnitudes of the theoretical covariance and sample covariance.

abs(rt)

`ans = `*4×4*
2.1259 1.8181 1.9261 1.9754
1.8181 2.1000 1.5263 1.9261
1.9261 1.5263 2.1000 1.8181
1.9754 1.9261 1.8181 2.0794

abs(r)

`ans = `*4×4*
2.2107 1.7961 2.0205 1.9813
1.7961 1.9858 1.5163 1.8384
2.0205 1.5163 2.1762 1.8072
1.9813 1.8384 1.8072 2.0000

### Correlation of Noise Between Sensors

Simulate receiving a signal at a ULA, where the noise between different sensors is correlated.

Create a 4-element uniform linear array whose elements are spaced one-half wavelength apart.

pos = 0.5 * (0:3);

Define the noise covariance matrix. The value in the ( *k*,_j_) position in the `ncov`

matrix is the covariance between the *k* and *j* array elements listed in array.

ncov = 0.1 * [1 0.1 0 0; 0.1 1 0.1 0; 0 0.1 1 0.1; 0 0 0.1 1];

Simulate 100 snapshots of the received signal at the array. Assume that one incoming signal originates from 60° azimuth.

ns = 100; ang = 60; [x,rt,r] = sensorsig(pos,ns,ang,ncov);

View the theoretical and sample covariance matrices for the received signal.

rt,r

`rt = `*4×4 complex*
1.1000 + 0.0000i -0.9027 - 0.4086i 0.6661 + 0.7458i -0.3033 - 0.9529i
-0.9027 + 0.4086i 1.1000 + 0.0000i -0.9027 - 0.4086i 0.6661 + 0.7458i
0.6661 - 0.7458i -0.9027 + 0.4086i 1.1000 + 0.0000i -0.9027 - 0.4086i
-0.3033 + 0.9529i 0.6661 - 0.7458i -0.9027 + 0.4086i 1.1000 + 0.0000i

`r = `*4×4 complex*
1.1059 + 0.0000i -0.8681 - 0.4116i 0.6550 + 0.7017i -0.3151 - 0.9363i
-0.8681 + 0.4116i 1.0037 + 0.0000i -0.8458 - 0.3456i 0.6578 + 0.6750i
0.6550 - 0.7017i -0.8458 + 0.3456i 1.0260 + 0.0000i -0.8775 - 0.3753i
-0.3151 + 0.9363i 0.6578 - 0.6750i -0.8775 + 0.3753i 1.0606 + 0.0000i

## Input Arguments

`pos`

— Positions of elements in sensor array

1-by-N vector | 2-by-N matrix | 3-by-N matrix

Positions of elements in sensor array, specified as an N-column
vector or matrix. The values in the matrix are in units of signal
wavelength. For example, `[0 1 2]`

describes three
elements that are spaced one signal wavelength apart. N is the number
of elements in the array.

Dimensions of `pos`

:

For a linear array along the y axis, specify the y coordinates of the elements in a 1-by-N vector.

For a planar array in the yz plane, specify the y and z coordinates of the elements in columns of a 2-by-N matrix.

For an array of arbitrary shape, specify the x, y, and z coordinates of the elements in columns of a 3-by-N matrix.

**Data Types: **`double`

`ns`

— Number of snapshots of simulated signal

positive integer scalar

Number of snapshots of simulated signal, specified as a positive integer scalar. The function returns this number of samples per array element.

**Data Types: **`double`

`ang`

— Directions of incoming plane wave signals

1-by-M vector | 2-by-M matrix

Directions of incoming plane wave signals, specified as an M-column vector or matrix in degrees. M is the number of incoming signals.

Dimensions of `ang`

:

If

`ang`

is a 2-by-M matrix, each column specifies a direction. Each column is in the form`[azimuth; elevation]`

. The azimuth angle must be between –180 and 180 degrees, inclusive. The elevation angle must be between –90 and 90 degrees, inclusive.If

`ang`

is a 1-by-M vector, each entry specifies an azimuth angle. In this case, the corresponding elevation angle is assumed to be 0.

**Data Types: **`double`

`ncov`

— Noise characteristics

0 (default) | nonnegative scalar | 1-by-N vector of positive numbers | N-by-N positive definite matrix

Noise characteristics, specified as a nonnegative scalar, 1-by-N vector of positive numbers, or N-by-N positive definite matrix.

Dimensions of `ncov`

:

If

`ncov`

is a scalar, it represents the noise power of the white noise across all receiving sensor elements, in watts. In particular, a value of`0`

indicates that there is no noise.If

`ncov`

is a 1-by-N vector, each entry represents the noise power of one of the sensor elements, in watts. The noise is uncorrelated across sensors.If

`ncov`

is an N-by-N matrix, it represents the covariance matrix for the noise across all sensor elements.

**Data Types: **`double`

`scov`

— Incoming signal characteristics

1 (default) | positive scalar | 1-by-M vector of positive numbers | M-by-M positive semidefinite matrix

Incoming signal characteristics, specified as a positive scalar, 1-by-M vector of positive numbers, or M-by-M positive semidefinite matrix.

Dimensions of `scov`

:

If

`scov`

is a scalar, it represents the power of all incoming signals, in watts. In this case, all incoming signals are uncorrelated and share the same power level.If

`scov`

is a 1-by-M vector, each entry represents the power of one of the incoming signals, in watts. In this case, all incoming signals are uncorrelated with each other.If

`scov`

is an M-by-M matrix, it represents the covariance matrix for all incoming signals. The matrix describes the correlation among the incoming signals. In this case,`scov`

can be real or complex.

**Data Types: **`double`

`taper`

— Array element taper

1 (default) | scalar | *N*-by-1 column vector

Array element taper, specified as a scalar or complex-valued *N*-by-1
column vector. The dimension *N* is the number of
array elements. If `taper`

is a scalar, all elements
in the array use the same value. If `taper`

is
a vector, each entry specifies the taper applied to the corresponding
array element.

**Data Types: **`double`

**Complex Number Support: **Yes

## Output Arguments

`x`

— Received signal

complex `ns`

-by-N matrix

Received signal at sensor array, returned as a complex `ns`

-by-N
matrix. Each column represents the received signal at the corresponding
element of the array. Each row represents a snapshot.

`rt`

— Theoretical covariance matrix

complex N-by-N matrix

Theoretical covariance matrix of the received signal, returned as a complex N-by-N matrix.

`r`

— Sample covariance matrix

complex N-by-N matrix

## More About

### Azimuth Angle, Elevation Angle

The *azimuth angle* of a vector is the angle between
the *x*-axis and the orthogonal projection of the vector onto the
*xy* plane. The angle is positive in going from the
*x* axis toward the *y* axis. Azimuth angles lie
between –180 and 180 degrees. The *elevation angle* is the angle
between the vector and its orthogonal projection onto the *xy*-plane. The
angle is positive when going toward the positive *z*-axis from the
*xy* plane. By default, the boresight direction of an element or array
is aligned with the positive *x*-axis. The boresight direction is the
direction of the main lobe of an element or array.

**Note**

The elevation angle is sometimes defined in the literature as the angle a vector makes
with the positive *z*-axis. The MATLAB^{®} and Phased Array System Toolbox™ products do not use this definition.

This figure illustrates the azimuth angle and elevation angle for a vector shown as a green solid line.

## Extended Capabilities

### C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

Does not support variable-size inputs.

## Version History

**Introduced in R2012b**

## See Also

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