plotThreshold

Plot preamble detection signals for triggering

Since R2022a

Syntax

``plotThreshold(pd,length)``
``droppedSamples = plotThreshold(pd,length)``

Description

example

````plotThreshold(pd,length)` plots preamble detection signals while detecting a preamble in live data of length `length` from the air using the preamble detector `pd`. The plot shows the correlator output power, threshold, and trigger points of the detection. Use the displayed information to calibrate the threshold in the preamble detector for triggering.```
````droppedSamples = plotThreshold(pd,length)` returns the status information of dropped samples, in addition to plotting preamble detection signals.```

Examples

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Define a preamble sequence with good correlation properties. For example, generate and normalize a Zadoff-Chu sequence of length 137.

```zcseq = zadoffChuSeq(38,137); preamble = zcseq/norm(zcseq,2); ```

Create and configure a preamble detector object, specifying a radio setup configuration previously saved in the Radio Setup wizard.

`pd = preambleDetector("MyRadio")`
```pd = preambleDetector with properties: CenterFrequency: 2.4000e+09 RadioGain: 10 Antennas: "RF0:RX2" SampleRate: 250000000 CaptureDataType: "int16" DroppedSamplesAction: "error" Preamble: [16×1 double] ThresholdMethod: "adaptive" FixedThreshold: 0 AdaptiveThresholdOffset: 0 AdaptiveThresholdGain: 0 TriggerOffset: 0 ```
```pd.SampleRate = 30.72e6; pd.RadioGain = 30;```

Specify the preamble.

`pd.Preamble = preamble;`

Specify a fixed threshold.

```pd.ThresholdMethod = "Fixed"; pd.FixedThreshold = 0.1;```

Generate test waveform for detection.

```prePadLen = 2501; postPadLen = 2500; headSignal = complex(zeros(prePadLen,1),zeros(prePadLen,1)); rearSignal = complex(zeros(postPadLen,1),zeros(postPadLen,1)); testWaveform = [headSignal; zcseq*0.75; rearSignal]; ```

Send the test waveform continuously.

```transmit(pd,testWaveform,"continuous", ... TransmitGain=30);```

Plot the specified number of samples of the correlator output power. Use the displayed information to calibrate thresholding parameters.

`plotThreshold(pd,10000);`

Stop test waveform transmission.

`stopTransmission(pd);`

Input Arguments

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Preamble detector, specified as a `preambleDetector` object.

Note

The first object function call in which you specify this object as an input requires a few extra seconds to load the application onto the hardware.

Plotted data length, specified as an integer number of samples or a `duration` value in time units. The function converts `length` into N samples based on the `pd``.SampleRate` property and plots `ceil`(N) number of data samples.

Specify the plotted data length relative to the onboard radio memory buffer size.

Radio DeviceMemory Buffer SizeMaximum Data Samples

USRP™ N310

2 GB229

USRP N320

2 GB229

USRP N321

2 GB229

USRP X310

1 GB228

USRP X410

4 GB230

Note

Plotted and transmit data samples are buffered in the onboard radio memory. Therefore, when specifying the plotted data length, you must also take into account the length of the transmit waveform of any continuous transmission that you specify when calling the `transmit` object function with the `pd` input.

Example: `seconds(5)`

Data Types: `double` | `duration`

Output Arguments

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Status of dropped samples, returned as one of these logical values.

• `1` — Samples are dropped while plotting the signals.

• `0` — Samples are not dropped while plotting the signals.

Use the `DroppedSamplesAction` property of the `pd` input to specify the behavior of the `plotThreshold` function upon dropped samples.

Data Types: `logical`

Version History

Introduced in R2022a