energyDetector
Description
Use the energyDetector
object to configure the specified
software-defined radio (SDR) as an energy detector. You can use the energy detector to detect
and capture a signal of interest from the air using an increase in signal energy as the
trigger. The object specifies the energy threshold and triggering parameters. For details, see
Internal Architecture of Energy Detection.
This diagram shows a conceptual overview of detecting and capturing radio signals in Wireless Testbench™ using a radio that you configure with this object. The object also enables you to send a test waveform for detection and capture. The onboard data buffering ensures contiguous data capture and transmit.
Creation
Description
creates an energy detector configuration object for the specified radio,
ed
= energyDetector(radio
)radio
.
Note
The object requires exclusive access to radio hardware resources. Before creating this object, clear any existing Wireless Testbench object associated with the specified radio from the workspace.
sets properties using one
or more name-value arguments. For example, ed
= energyDetector(radio
,Name=Value
)CaptureDataType="double"
sets the data type of the returned captured signal to double
.
Input Arguments
radio
— Radio setup configuration
string scalar
Radio setup configuration, specified as a string scalar. To create a radio setup
configuration, set up your radio and save your radio setup configuration using the Radio Setup
wizard. To list all saved radio setup configurations, call the radioConfigurations
function.
For a list of supported radios, see Supported Radio Devices.
Example: "MyRadio"
indicates that you saved a radio setup
configuration under the name MyRadio in the Radio Setup wizard.
Properties
CenterFrequency
— Capture center frequency in Hz
2.4e9
(default) | positive numeric scalar
Capture center frequency in Hz, specified as a positive numeric scalar. The valid center frequency range depends on the radio device.
Radio Device | Center Frequency |
---|---|
USRP™ N310 | 1 MHz to 6 GHz |
USRP N320 | 1 MHz to 6 GHz |
USRP N321 | 1 MHz to 6 GHz |
USRP X310 | 10 MHz to 6 GHz |
USRP X410 | 1 MHz to 8 GHz |
Data Types: double
RadioGain
— Capture radio gain in dB
10
(default) | positive numeric scalar
Capture radio gain in dB, specified as a positive numeric scalar. The valid gain range depends on the radio device.
Radio Device | Capture Radio Gain |
---|---|
USRP N310 | 0 dB to 75 dB |
USRP N320 | 0 dB to 60 dB |
USRP N321 | 0 dB to 60 dB |
USRP X310 | 0 dB to 31.5 dB |
USRP X410 | 0 dB to 60 dB |
Data Types: double
Antennas
— Capture radio antenna
string scalar
Capture radio antenna, specified as a string scalar. Use this table to identify a supported radio antenna port on the radio device and the corresponding string constant that you can specify for this property. The default value depends on the radio.
Radio Device | Supported Antenna Port | String Scalar |
---|---|---|
USRP N310 | RF0 channel: RX2 port | "RF0:RX2" (default) |
RF1 channel: RX2 port | "RF1:RX2" | |
RF2 channel: RX2 port | "RF2:RX2"
| |
RF3 channel: RX2 port | "RF3:RX2" | |
USRP N320 | RF0 channel: RX2 port | "RF0:RX2" (default) |
RF1 channel: RX2 port | "RF1:RX2" | |
USRP N321 | RF0 channel: RX2 port | "RF0:RX2" (default) |
RF1 channel: RX2 port | "RF1:RX2" | |
USRP X310 | RFA channel: RX2 port |
|
RFB channel: RX2 port |
| |
USRP X410 | DB0 RF0 channel: RX 1 port |
|
DB0 RF1 channel: RX 1 port |
| |
DB1 RF0 channel: RX 1 port |
| |
DB1 RF1 channel: RX 1 port |
|
Note
When you update this property, the execution time of the next object function call increases by a few seconds.
Data Types: string
SampleRate
— Baseband sample rate in Hz
highest device sample rate (default) | positive numeric scalar
Baseband sample rate in Hz, specified as a positive numeric scalar. For more information on how the radio achieves the specified sample rate, see Baseband Sample Rate in NI USRP Radios.
The sample rate depends on the radio device.
Radio Device | Sample Rate |
---|---|
USRP N310 |
|
USRP N320 |
|
USRP N321 |
|
USRP X310 |
|
USRP X410 |
|
Note
To update this property, you must stop any ongoing transmission by calling the stopTransmission
function on the object. When you update this property, the execution time of the next object
function call increases by a few seconds.
Data Types: double
CaptureDataType
— Data type of captured data
"int16"
(default) | "double"
| "single"
Data type of the captured data, specified as "int16"
,
"double"
, or "single"
. Use this property to
set the data type of the captured data that the capture
object function returns.
Note
When you update this property, the execution time of the next object function call increases by a few seconds.
Data Types: string
TimestampUnit
— Unit of capture request timestamp
"datetime"
(default) | "sample-clock-cycle"
Since R2024a
Unit of capture request timestamp, specified as "datetime"
or
"sample-clock-cycle"
. Use this property to set the data type of the
timestamp that the capture
object
function returns.
Data Types: string
DroppedSamplesAction
— Behavior upon dropped samples
"error"
(default) | "warning"
| "none"
Behavior of the capture
or
plotDetectionSignals
object functions upon dropped samples, specified as
one of these values.
"error"
— The object function stops with an error message."warning"
— The object function displays a warning message."none"
— The object function ignores dropped samples.
Data Types: string
WindowLength
— Energy integration window length
300
(default) | numeric scalar in the range [0, 4095]
Energy integration window length, specified as a numeric scalar in the range [0, 4095]. The number of samples in the sliding window that is used to calculate the signal energy and the energy increase. For details, see Thresholding and Triggering.
Data Types: double
ThresholdMethod
— Threshold calculation method
"adaptive"
(default) | "fixed"
Threshold calculation method to trigger data capture, specified as one of these values.
"adaptive"
— Two thresholds must be met to trigger a data capture. The energy increase in dB, which is the ratio between the signal energy in the current window and the signal energy in the previous window, is compared against a constant threshold specified by theEnergyDeltaThreshold
property. The signal energy is also compared against a constant threshold, specified by theMinimumEnergy
property. Together, these thresholds are adaptive to channel noise."fixed"
— The signal energy is compared against a constant threshold, specified by theFixedThreshold
property.
For details, see Algorithms.
Note
To update this property, you must stop any ongoing transmission by calling the stopTransmission
function on the object. When you update this property, the execution time of the next object
function call increases by a few seconds.
Data Types: string
FixedThreshold
— Fixed threshold value
1e-4
(default) | numeric scalar in the range [0, 8191]
Fixed threshold value, specified as a numeric scalar in the range [0, 8191]. For details, see Thresholding and Triggering.
Dependencies
This property applies only when you set ThresholdMethod
to "fixed"
.
Data Types: double
MinimumEnergy
— Minimum energy threshold value
1e-4
(default) | numeric scalar in the range [0, 8191]
Minimum energy threshold value, specified as a numeric scalar in the range [0,
8191]. This value is the minimum energy at which the EnergyDeltaThreshold
is applied in adaptive threshold mode. Set this
threshold relative to the noise floor so that noise variations under this level do not
cause false triggers. For details, see Thresholding and Triggering.
Dependencies
This property applies only when you set ThresholdMethod
to "adaptive"
.
Data Types: double
EnergyDeltaThreshold
— Energy increase threshold in dB
1
(default)
Energy delta threshold, specified as the energy increase threshold in dB. This value
is the ratio between the signal energy in the current window and the signal energy in
the previous window, expressed in decibels. Set this threshold relative to the WindowLength
property. For example:
An energy increase of 3 dB corresponds to a two-fold increase in signal energy between two adjacent windows.
An energy increase of 20 dB corresponds to a one-hundred-fold increase in signal energy between two adjacent windows.
For details, see Thresholding and Triggering.
Dependencies
This property applies only when you set ThresholdMethod
to "adaptive"
.
Data Types: double
TriggerOffset
— Trigger point offset
0
(default) | integer in the range [–4095, 4096]
Trigger point offset, specified as an integer in the range [–4095, 4096]. This value specifies the start of data capture relative to the trigger point. For details, see Thresholding and Triggering.
Note
To update this property, you must stop any ongoing transmission by calling the stopTransmission
function on the object. When you update this property, the execution time of the next object
function call increases by a few seconds.
Data Types: double
Object Functions
capture | Capture signal of interest from the air upon detection |
plotDetectionSignals | Plot energy detection signals for triggering |
transmit | Transmit waveform using preamble or energy detector |
stopTransmission | Stop transmission from preamble or energy detector |
Examples
Configure Energy Detector and Capture Data
Create and configure an energy detector object, specifying a radio setup configuration previously saved in the Radio Setup wizard.
ed = energyDetector("MyRadio")
ed = energyDetector with properties: Antennas: "RF0:RX2" CenterFrequency: 2.4000e+09 SampleRate: 250000000 RadioGain: 10 CaptureDataType: "int16" WindowLength: 300 TriggerOffset: 0 DroppedSamplesAction: "error" ThresholdMethod: "adaptive" TimestampUnit: "datetime" MinimumEnergy: 1.0000e-04 EnergyDeltaThreshold: 1
ed.SampleRate = 30.72e6;
ed.CenterFrequency = 2.45e9;
ed.CaptureDataType = "double";
Set the energy increase threshold to 3 dB.
ed.EnergyDeltaThreshold = 3;
Set the trigger offset to a negative value to capture 100 samples before the trigger point.
ed.TriggerOffset = -100;
Capture 3 ms of data with a timeout of 1 second.
[data,timestamp,droppedSamples,status] = capture(ed,milliseconds(3),seconds(1));
Capture Multiple Consecutive Signals with Energy Detector
Create and configure an energy detector object, specifying a radio setup configuration previously saved using the Radio Setup wizard. Set the data type of the captured data to double and the unit of the capture request timestamp to sample clock cycles.
ed = energyDetector("MyRadio",CaptureDataType="double",TimestampUnit="sample-clock-cycle")
ed = energyDetector with properties: Antennas: "RF0:RX2" CenterFrequency: 2.4000e+09 SampleRate: 250000000 RadioGain: 10 CaptureDataType: "double" WindowLength: 300 TriggerOffset: 0 DroppedSamplesAction: "error" ThresholdMethod: "adaptive" TimestampUnit: "sample-clock-cycle" MinimumEnergy: 1.0000e-04 EnergyDeltaThreshold: 1
Capture five consecutive signals that meet the default thresholding criteria with a capture length of 1 ms and a timeout of 1 s.
[data,timestamp,droppedSamples,status] = capture(ed,milliseconds(1),seconds(1),"NumCaptures",5);
Tips
You
cannot use save
and load
to store and reload
Wireless Testbench objects. Instead, you can
re-create the object with these steps:
Write code to create a
energyDetector
object with a saved radio setup configurationradio
and set the properties.Save the code to a script.
Run the script in a new MATLAB® session with the same saved radio setup configuration.
Algorithms
Internal Architecture of Energy Detection
This diagram shows a conceptual overview of a triggered capture based on energy detection. The input is an RF signal received by the radio.
The Data integration component calculates the energy in the received signal by integrating the input data over the window length specified by the
WindowLength
property. This component also calculates the signal energy in the previous window, and the ratio between the signal energy in the current window and the signal energy in the previous window.The Threshold component provides two thresholds for the trigger point generation. The energy threshold is set by the
MinimumEnergy
property when theThresholdMethod
property is set to"adaptive"
, or theFixedThreshold
property when theThresholdMethod
is set to"fixed"
. This component also calculates the ratio threshold by converting theEnergyDeltaThreshold
property from a dB value to a ratio.The Capture controller component controls the triggered capture.
The Comparators generate the trigger point using the energy threshold and the ratio threshold when the
ThresholdMethod
property is set to"adaptive"
, or the energy threshold only when theThresholdMethod
property is set to"fixed"
. The trigger point is the first data sample for which thresholding conditions have been met.The Data packaging component starts the data capture. To adjust the start of the data capture relative to the trigger point, use the
TriggerOffset
property.
Thresholding and Triggering
The trigger point is the first data sample for which the thresholding conditions are met. To calibrate the thresholding and triggering operation:
Adjust the gain on the RF signal by using the
RadioGain
property.Adjust the threshold. You can specify an adaptive threshold or a fixed threshold.
To trigger data capture on an increase in signal energy, set the
ThresholdMethod
property to"adaptive"
. The energy increase in dB is calculated by finding the ratio between the energy in the current window and the energy in the previous window, and converting to dB. Set theMinimumEnergy
andEnergyDeltaThreshold
properties. The figure shows an example of a signal energy measurement and the associated thresholds that leads to a detection.To trigger data capture when the signal energy crosses a fixed threshold, set the
ThresholdMethod
property to"fixed"
, and then use theFixedThreshold
property to set the fixed threshold value.
Call the
plotDetectionSignals
object function to display and analyze the signals, thresholds, and corresponding trigger points.
By default, data capture starts at the trigger point. To adjust the start of the data
capture relative to the trigger point, use the TriggerOffset
property. For example, this figure shows a scenario in which the trigger offset is 0.
Therefore, data capture starts at the first detection point.
In this second scenario, the trigger point is the same, but the trigger offset is –50. Therefore, data capture starts at the specified trigger offset.
Version History
Introduced in R2023bR2024a: Specify the unit of the capture request timestamp with TimestampUnit
The capture
object
function can now capture multiple consecutive signals with an energyDetector
object. Set the TimestampUnit
property to "sample-clock-cycle"
to
return the capture
function
output argument timestamp
as an
integer number of sample clock cycles.
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