plotTDOASpectrum

Create and plot signal time-difference-of-arrival (TDOA) spectrum

Since R2024b

Syntax

[tdoagrid,tdoaspectrum,tdoaest] = plotTDOASpectrum(estimate)

[tdoagrid,tdoaspectrum,tdoaest] = plotTDOASpectrum(estimate,Name=Value)

Description

Create and plot the signal time-difference-of-arrival (TDOA) spectrum for anchor pair.

[tdoagrid,tdoaspectrum,tdoaest] = plotTDOASpectrum(estimate) creates and plots the time-difference-of-arrival (TDOA) grid, tdoagrid, the TDOA spectrum, tdoaspectrum, and the estimated TDOA, tdoaest, for the first anchor pair derived from the phased.TDOAEstimator System object™ estimate.

To use this function, first create and execute the phased.TDOAEstimator System object.

[tdoagrid,tdoaspectrum,tdoaest] = plotTDOASpectrum(estimate,Name=Value) also specifies one or more Name-Value arguments, in addition to the input arguments from the previous syntax . For example, AnchorPairIndex=4 specifies the fourth anchor pair in the channel (see Name-Value Arguments). You can specify multiple name-value pair arguments in any order as Name1=Value1,...,NameN=ValueN.

Examples

Plot Spectrum for Estimated Time-Differences of Arrival

Start with signals from five anchors with known positions. Perform TDOA estimation by applying the GCC-PHAT algorithm in phased.TDOAEstimator System object™ on the received signals from a target. The TOAEstimatorExampleData mat-file contains the variables needed in this example:

Xtime	Time-domain received signals
fs	Sample rate (Hz)
toa	Time-of-arrival at each anchor
anchorpos	Anchor positions
npow	Noise power

Load data from the mat-file.

load TOAEstimatorExampleData

Plot the anchor positions and target position.

plot3(anchorpos(1,:),anchorpos(2,:),anchorpos(3,:),'*')
hold on
plot3(anchorpos(1,1),anchorpos(2,1),anchorpos(3,1),'*g')

plot3(tgtpos(1),tgtpos(2),tgtpos(3),'.')
xlabel('x (meters)')
ylabel('y (meters)')
zlabel('z (meters)')
hold off
legend('anchors','reference','target')

Create a TDOA estimator.

estimator = phased.TDOAEstimator(SampleRate=fs,NumEstimates=1, ...
    VarianceOutputPort=true,NoisePower=npow);

Perform the TDOA estimation.

tdoaest = estimator(Xtime)*10^9;

Obtain the true TDOA in ns from the mat-file.

tdoatruth = (toa(2:end) - toa(1))*10^9

tdoatruth = 1×4

   55.7611   58.8663   69.5528   43.5516

tdif = tdoaest - tdoatruth

tdif = 1×4

    0.2389    0.1337    0.4472    0.4484

Plot the TDOA spectrum for the first anchor pair (default).

plotTDOASpectrum(estimator)

Overlay the plot of the TDOA spectrum for the second anchor pair.

plotTDOASpectrum(estimator,AnchorPairIndex=2)

Input Arguments

estimate — TDOA estimator

phased.TDOAEstimator System object

TDOA estimator, specified as a phased.TDOAEstimator System object.

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: plotTDOASpectrum(estimator,freqspacing,AnchorPairIndex=4) specifies the fourth anchor pair in the channel.

AnchorPairIndex — Anchor index

1 (default) | positive integer

Anchor pair index, specified as a positive integer from 1 to L–1 where L is the number of anchors.

Example: AnchorPairIndex=4

Data Types: single | double

MaxDelay — Maximum delay difference (seconds)

positive scalar

Maximum delay difference in the TDOA spectrum, specified as a positive scalar. The default value is the maximum unambiguous delay difference. Units are in seconds.

Example: MaxDelay=1e-6

Data Types: double

Output Arguments

tdoagrid — TDOA grid (seconds)

P-by-L matrix | 1-by-L cell array

Time-difference-of-arrival grid, returned as a P-by-1 real-valued vector. All returned TDOA values lie on this grid. The function determines the value of P. Units are in seconds.

Data Types: single | double

tdoaspectrum — TDOA spectrum (Hz)

P-by-1 real-valued vector

TDOA spectrum, returned as a P-by-1 real-valued vector. The function determines the value of P. Units are in Hz.

tdoaest — TDOA estimate (seconds)

scalar

TDOA estimate, returned as a scalar. Units are in seconds.

Data Types: single | double

Version History

Introduced in R2024b