basebandPhaseAnalyzer

Measure relative phase offsets between baseband waveforms

Since R2026a

Description

Use the basebandPhaseAnalyzer object to measure the relative phase offset between two or more channels across one or more synchronized radios. You can configure the object to analyze capture antennas using an external or known stimulus or to analyze transmit antennas by capturing the emitted signal using a monitor antenna.

The object connects radio application objects to antennas for phase analysis.

To set up the basebandPhaseAnalyzer object, follow these steps:

1. Create a basebandTransceiver application object for your radio or radios. This application object configures your radio to simultaneously transmit and capture IQ waveforms over the air.

2. If you are using multiple radios, synchronize the radio time. For details, see Time-Synchronize Operations.

3. Specify basebandPhaseAnalyzer object properties:

   • Specify the radio or radios for phase analysis.

   • To perform capture antenna phase analysis, specify the radio and antenna to transmit a stimulus signal. Alternatively, you can use an external stimulus.

   • To perform transmit antenna phase analysis, specify the radio and antenna as a monitor to capture the transmitted signals.

To perform phase analysis, use the measureAntennaPhase object function. For more information about how the phase analysis is performed, see Capture Calibration and Transmit Calibration.

The results of the phase analysis are estimated phase offsets for each antenna under test relative to the first antenna of the first radio. You can use these estimates to apply a correction to future transmissions or captured data.

• In phase-coherent systems, you can achieve phase calibration using this method.

• In systems that are not phase-coherent, the phase offset of each antenna drifts over time due to hardware and environmental factors. Rerun the function periodically or after you make changes to the hardware to maintain the accuracy of the phase calibration.

For more information, see Phase-Synchronize Operations.

Creation

Syntax

analyzer = basebandPhaseAnalyzer

analyzer = basebandPhaseAnalyzer(PropertyName=Value)

Description

analyzer = basebandPhaseAnalyzer creates an empty phase analyzer object.

analyzer = basebandPhaseAnalyzer(PropertyName=Value) sets properties using one or more name-value arguments. For example, RadioApplications=[bbtrx1,bbtrx2] specifies the baseband transceiver objects bbtrx1 and bbtrx2 as the radio applications for phase analysis.

Properties

RadioApplications — Radios for phase analysis

basebandTransceiver object | vector of basebandTransceiver objects | cell array of basebandTransceiver objects

Radios for phase analysis, specified as one of these options:

• A scalar basebandTransceiver application object

• A vector of basebandTransceiver application objects

• A cell array of basebandTransceiver application objects

If you specify multiple radios, ensure that all radios are time-synchronized. For more information, see Time-Synchronize Operations.

Example: {bbtrx1, bbtrx2}

StimulusApplication — Radio used to transmit stimulus signal for capture antenna measurement

[] (default) | basebandTransceiver object

Radio used to transmit the stimulus signal for capture antenna measurement, specified as one of these options:

• [] (empty) — No stimulus application is specified. A stimulus application is not required to measure the relative phase offset of transmit antennas. To measure the relative phase offset of capture antennas without a stimulus application, you can use an external stimulus.

• basebandTransceiver application object — The baseband transceiver application object for transmitting a stimulus signal. Additionally specify the specific transmit antenna using the StimulusAntenna property.

Example: bbtrx2

StimulusAntenna — Antenna used to transmit stimulus signal

[] (default) | string scalar

Antenna used to transmit stimulus, specified as a string scalar. This antenna must correspond to an antenna specified in the TransmitAntennas property of the stimulus application object.

Example: "RF0:TX/RX"

Data Types: string

MonitorApplication — Radio used to capture monitor signal for transmit antenna measurement

[] (default) | basebandTransceiver object

Radio used to capture the monitor signal for transmit antenna measurement, specified as one of these options:

• [] (empty) — No monitor application is specified. A monitor application is not required to measure the relative phase offset of transmit antennas.

• basebandTransceiver application object — The baseband transceiver application object for capturing a monitor signal. Additionally specify the specific capture antenna using the MonitorAntenna property.

Example: bbtrx2

MonitorAntenna — Antenna used to capture monitor signal

[] (default) | string scalar

Antenna used to capture monitor signal, specified as a string scalar. This antenna must correspond to an antenna specified in the CaptureAntennas property of the monitor application object.

Example: "RF0:RX2"

Data Types: string

Object Functions

measureAntennaPhase

Estimate relative phase offsets of transmit or capture antennas

Examples

Create Phase Analyzer Object

Create a default phase analyzer object.

bbpa = basebandPhaseAnalyzer

bbpa = 
  basebandPhaseAnalyzer with properties:

       RadioApplication: {1×0 cell}
        StimulusAntenna: [0×0 string]
         MonitorAntenna: [0×0 string]
    StimulusApplication: [0×0 basebandTransceiver]
     MonitorApplication: [0×0 basebandTransceiver]

Specify a basebandTransceiver application object as the radio for phase analysis.

bbpa.RadioApplication = bbtrx;

To measure the phase offsets between capture antennas on your radio, specify a basebandTransceiver application object as the stimulus application, and specify the antenna to transmit the stimulus signal. This example uses a different radio to transmit the stimulus signal.

bbpa.StimulusApplication = bbtrx2;
bbpa.StimulusAntenna = "RF1:TX/RX";

To measure the phase offsets between transmit antennas on your radio, specify a basebandTransceiver application object as the monitor application. This example uses a different radio as a monitor.

bbpa.MonitorApplication = bbtrx2;
bbpa.MonitorAntenna = "RF1:RX2"

bbpa = 
  basebandPhaseAnalyzer with properties:

       RadioApplication: {[1×1 basebandTransceiver]}
        StimulusAntenna: "RF1:TX/RX"
         MonitorAntenna: "RF1:RX2"
    StimulusApplication: [1×1 basebandTransceiver]
     MonitorApplication: [1×1 basebandTransceiver]

Measure Relative Phase Offsets Between Transmit Antennas on Single Radio

This example shows how to measure relative phase offsets between transmit antennas on a single radio using the basebandPhaseAnalyzer object. The example uses a second USRP radio to capture the monitor signal.

Create Radio Objects

Create a radio object for each radio, specifying a radio setup configuration previously saved using the Radio Setup wizard.

radio = radioConfigurations("MyRadio");
radio2 = radioConfigurations("MyRadio2");

Specify Antennas

Define the antennas under test and the monitor antenna.

antennasUnderTest = ["RF0:TX/RX" "RF1:TX/RX"];
monitorAntenna = "RF1:RX2";

Configure Baseband Transceivers

Create and configure a basebandTransceiver application object for each radio. Use the same RF properties on both radios. Specify all RF properties using the PropertyName=Value syntax and preload the FPGA image.

transmitGain = 20;
captureGain = 30;

bbtrx = basebandTransceiver(radio, ...
    Preload=true, ...
    TransmitAntennas=antennasUnderTest, ...
    TransmitRadioGain=transmitGain);

bbtrx2 = basebandTransceiver(radio2, ...
    Preload=true, ...
    CaptureAntennas=monitorAntenna, ...
    CaptureRadioGain=captureGain);

Synchronize Radio Time

Synchronize both radios to a common time using the next PPS signal.

tLastPPS = getTimeLastPPS(radio);
while tLastPPS == getTimeLastPPS(radio)
    pause(0.1)
end
setTimeNextPPS(radio,0);
setTimeNextPPS(radio2,0);

Verify that the radio time is synchronized.

pause(1.1)
tLastPPS1 = getTimeLastPPS(radio);
tLastPPS2 = getTimeLastPPS(radio2);
isequal(tLastPPS1,tLastPPS2)

ans = logical
   1

If the radio time synchronization is unsuccessful, rerun this section.

Estimate Relative Phase Offsets

Create a phase analyzer object.

bbpa = basebandPhaseAnalyzer(RadioApplication=bbtrx, ...
    MonitorApplication=bbtrx2,MonitorAntenna=monitorAntenna);

Estimate the relative phase offsets of the specified transmit antennas and plot the measurement results.

[phase,results] = measureAntennaPhase(bbpa,"transmit")

phase = 1×1 cell array
    {[0 -60.0394]}

results = 1×1 cell array
    {72×2 double}

Measure Relative Phase Offsets Between Capture Antennas on Single Radio

This example shows how to measure relative phase offsets between capture antennas on a single radio using the basebandPhaseAnalyzer object. The example uses a second USRP radio to transmit the stimulus signal.

Create Radio Objects

Create a radio object for each radio, specifying a radio setup configuration previously saved using the Radio Setup wizard.

radio = radioConfigurations("MyRadio");
radio2 = radioConfigurations("MyRadio2");

Specify Antennas

Define the stimulus antenna and the antennas under test.

antennasUnderTest = ["RF0:RX2" "RF1:RX2"];
stimulusAntenna = "RF1:TX/RX";

Configure Baseband Transceivers

Create and configure basebandTransceiver application objects for each radio. Use the same RF properties on both radios. Specify all RF properties using the PropertyName=Value syntax and preload the FPGA image.

transmitGain = 20;
captureGain = 30;

bbtrx = basebandTransceiver(radio, ...
    Preload=true, ...
    CaptureAntennas=antennasUnderTest, ...
    CaptureRadioGain=captureGain);

bbtrx2 = basebandTransceiver(radio2, ...
    Preload=true, ...
    TransmitAntennas=stimulusAntenna, ...
    TransmitRadioGain=transmitGain);

Synchronize Radio Time

Synchronize both radios to a common time using the next PPS signal.

tLastPPS = getTimeLastPPS(radio);
while tLastPPS == getTimeLastPPS(radio)
    pause(0.1)
end
setTimeNextPPS(radio,0);
setTimeNextPPS(radio2,0);

Verify that the radio time is synchronized.

pause(1.1)
tLastPPS1 = getTimeLastPPS(radio);
tLastPPS2 = getTimeLastPPS(radio2);
isequal(tLastPPS1,tLastPPS2)

ans = logical
   1

If the radio time synchronization is unsuccessful, rerun this section.

Estimate Relative Phase Offsets

Create a phase analyzer object.

bbpa = basebandPhaseAnalyzer(RadioApplication=bbtrx, ...
    StimulusApplication=bbtrx2,StimulusAntenna=stimulusAntenna);

Estimate the relative phase offsets of the specified capture antennas and plot the measurement results.

phase = measureAntennaPhase(bbpa,"capture")

phase = 1×1 cell array
    {[0 171.6380]}

Measure Relative Phase Offsets Between Capture Antennas on Multiple Radios

This example shows how to measure relative phase offsets between capture antennas using the basebandPhaseAnalyzer object. The example uses a USRP N321 and USRP N320 radio with LO sharing configured.

Create Radio Objects

Create a radio object for each radio, specifying a radio setup configuration previously saved using the Radio Setup wizard.

radio1 = radioConfigurations("MyN321");
radio2 = radioConfigurations("MyN320");

Specify Antennas

Define the stimulus antenna and the antennas under test.

stimulusAntenna = "RF1:TX/RX";
antennasUnderTest_radio1 = "RF0:RX2";
antennasUnderTest_radio2 = ["RF0:RX2" "RF1:RX2"];

Configure Baseband Transceivers

Create and configure basebandTransceiver application objects for each radio. Use the same RF properties on both radios. Specify all RF properties using the PropertyName=Value syntax and preload the FPGA image.

transmitGain = 20;
captureGain = 30;

bbtrx1 = basebandTransceiver(radio1, ...
    Preload=true, ...
    CaptureAntennas=antennasUnderTest_radio1, ...
    CaptureRadioGain=captureGain, ...
    TransmitAntennas=stimulusAntenna, ...
    TransmitRadioGain=transmitGain);

bbtrx2 = basebandTransceiver(radio2, ...
    Preload=true, ...
    CaptureAntennas=antennasUnderTest_radio2, ...
    CaptureRadioGain=captureGain);

Synchronize Radio Time

Synchronize both radios to a common time using the next PPS signal.

tLastPPS = getTimeLastPPS(radio1);
while tLastPPS == getTimeLastPPS(radio1)
    pause(0.1)
end
setTimeNextPPS(radio1,0);
setTimeNextPPS(radio2,0);

Verify that the radio time is synchronized.

pause(1.1)
tLastPPS1 = getTimeLastPPS(radio1);
tLastPPS2 = getTimeLastPPS(radio2);
isequal(tLastPPS1,tLastPPS2)

ans = logical
   1

If the radio time synchronization is unsuccessful, rerun this section.

Estimate Relative Phase Offsets

Create a phase analyzer object.

bbpa = basebandPhaseAnalyzer(RadioApplication={bbtrx1,bbtrx2}, ...
    StimulusApplication=bbtrx1,StimulusAntenna=stimulusAntenna);

Estimate the relative phase offsets of the specified capture antennas and plot the measurement results.

phase = measureAntennaPhase(bbpa,"capture",PlotResult=true, ...
    Antennas={antennasUnderTest_radio1 antennasUnderTest_radio2});

Display Results

Display the measured phase offsets in degrees.

disp("Measured phase estimates: ["+num2str(phase{1}(1))+" " + ...
    ""+num2str(phase{2}(1))+", "+num2str(phase{2}(2))+"]")

Measured phase estimates: [0 -74.5732, -84.5957]

Algorithms

The basebandPhaseAnalyzer object estimates the relative phase offset between antennas by analyzing the frequency-domain interference of wideband signals. The object supports both capture and transmit calibration workflows.

Capture Calibration

The basebandPhaseAnalyzer object performs capture antenna phase offset estimation by using the following process.

Stimulus Generation and Transmission

If you specify a radio and transmit antenna using the StimulusApplication and StimulusAntenna properties, the software generates and transmits a band-limited white noise signal. If you do not specify a stimulus application, you must use an externally transmitted stimulus signal instead.

Synchronized Capture

The software synchronizes the capture of the stimulus signal across all capture antennas or the antennas specified using the Antennas name-value argument. These are the steps:

1. Identify antennas for measurement.

2. Schedule a capture on all radios. By default, the capture length is equal to SampleRate/250. To specify a different capture length, specify the SamplesPerAntenna name-value argument.

3. Wait for the capture to complete.

4. Retrieve the captured data.

Phase Sweep

To remove non-steady-state effects, the software discards the first 500 samples from each data set. The software uses the first antenna as the reference. For each remaining antenna, the software estimates the relative offset by sweeping phase shifts and comparing spectra. These are the steps:

1. Apply a phase shift by multiplying the waveform by a complex exponential.

2. Sweep phase offsets. By default, the sweep runs from –180° to 180° in 5° increments. To refine the sweep, specify InitialEstimate, StepSize, and NumSteps.

3. Compute the FFT of each phase-shifted waveform.

4. Compare each magnitude spectrum with the reference spectrum.

5. Compute the mean spectrum magnitude difference at each phase step.

6. Return the full matrix of results in the results output argument.

Phase Offset Estimation

The software estimates the relative phase offset for each antenna using a fractional peak estimation. These are the steps:

1. Identify the phase step that minimizes the mean spectrum magnitude.

2. Fit a parabola to the three lowest points to refine the estimate.

The software returns the estimated phase offsets in the phase output argument. If the PlotResult name-value argument is set to true, the software plots the results and returns the plot handles in the figures output.

Transmit Calibration

The basebandPhaseAnalyzer object performs transmit antenna phase offset estimation using the following process.

Reference Waveform Generation

The software generates a band-limited white noise signal to transmit from each antenna.

Transmit and Capture with Phase Sweep

For each antenna, the software performs a transmit-and-capture sweep through a range of phase offsets. These are the steps:

1. Apply the phase offset to the reference waveform.

2. Transmit the phase-shifted waveform on the antenna under test.

3. Capture the transmitted signal on the antenna specified by the MonitorApplication and MonitorAntenna properties. By default, the capture length is SampleRate/250. To use a different capture length, specify the SamplesPerAntenna name-value argument.

4. Sweep phase offsets. By default, the sweep runs from –180° to 180° in 5° increments. To refine the sweep, specify InitialEstimate, StepSize, and NumSteps.

The software returns the full matrix of sweep results in the results output argument.

Spectra Comparison

To remove non-steady-state effects, the software discards the first 500 samples from each captured data set. The software uses the first antenna as a reference. These are the steps:

1. Compute an FFT of the capture data from the first antenna to use as the reference spectrum.

2. For each remaining antenna and phase step, compute an FFT of the captured data.

3. Compare each magnitude spectrum with the reference spectrum.

4. Compute the mean spectrum magnitude difference at each phase step.

Phase Offset Estimation

The software estimates the relative phase offset for each antenna using a fractional peak estimation. These are the steps:

1. Identify the phase step that minimizes the mean spectrum magnitude.

2. Fit a parabola to the three lowest points to refine the estimate.

The software returns the estimated phase offsets in the phase output argument. If the PlotResult name-value argument is set to true, the software plots the results and returns the plot handles in the figures output.

Version History

Introduced in R2026a