gr-power

GNU radio power library.

Currently only contains two GNU radio blocks: Moving RMS and power stats.

Also contains one tool: gr-power-burst-recorder

GNU radio blocks

Moving RMS

Moving RMS is an alternative to the standard RMS block that comes with GNU Radio.

The standard RMS block calculates a first-order recursive average of the input whereas the moving RMS block use a Moving Average (MA) calculation of the RMS value.

The recursive average can be viewed as an IIR filter approximation of the true RMS value.

A Moving Average with a rectangular window is a special case of a regular FIR filter where all filter coefficients are set to 1/N. N is the length of the filter (the number of values to be used in the average calculation).

Since a rectangular window is used, the implementation can be made quite efficient.

Power stats

Power stats provides two statistics probe functions:

• Duty cycle
• Burst count

Duty cycle is the percentage of time when the input signal is above a configurable threshold.

The burst count is the number of detected power bursts over time.

All statistics probe functions have a delta_ version that is used to read the difference since the last probe call.

See section GNURadioCompanion. for more details on usage,

Build

It is recommended to build GNU Radio modules in a build directory outside the source tree:

mkdir build
cd build
cmake ..
make
sudo make install
sudo ldconfig

GNURadioCompanion

Moving RMS

The Moving RMS block can be found under the Power section in GRC.

There is currently only one configuration parameter for the block: Averaging history length

This is the number of values that will be used in the calculation of the average, i.e, the filter length N.

Power stats

The Power stats block provide a set of statistics probe functions (as described above).

The probe functions should be called periodically from a Function Probe block and the obtained vales can be added to an appropriate GUI widget (like QT GUI Entry) for display.

The available probe functions are:

• burst_count
• delta_burst_count
• avg_duty_cycle
• delta_avg_duty_cycle

Each function should be called without arguments.

In a Function Probe block, set the Block ID and Function Name according to below:

Block ID = <ID value of the Power stats block>
Function Name = <probe function to poll>

In a QT GUI Entry block, set the Default Value according to below:

Default Value = <ID value of the Function Probe block>

Tools

The tools subdirectory contains stand-alone tools (no dependecies to any gnuradio libraries).

Currently only one tool is included: gr-power-burst-recorder

gr-power-burst-recorder

Usage: gr-power-burst-recorder OPTIONS

gr-power-burst-recorder is a tool used to extract bursts from an input and write those bursts to an output. It can also be used to detect bursts from the input and report info (burst count and lengths) to stdout A burst is a series of samples with a power significantly higher than the other samples in a data stream The input is a sequence of float's where each tuple is a pair of iq samples.

The program has 2 modes of operation: recording and detection. Detection is the default mode (when launched without the --record option)

During detection, samples from input will be power estimated with a moving RMS value calculation. The start and end (sample offsets) and length of each burst will be printed to stdout.

During recording, the same type of detection will be performed, but no reporting will be made. Instead, when the burst specified with the --record-burst-nbr option is found, it will be recorded and the program will terminate.

The recommended usage of the program is to first run without --record in order to get an overview of the contents of the file. Then, run again with the --record option in order to record the burst of interest. It is important that the same settings are used for both the detection and recording. Otherwise, different bursts might be detected (and recorded) in the recording phase.

In the case of recording, the program will terminate when the burst specified by the --record-burst-nbr has been recorded.

The arguments --detection-threshold-high and --detection-threshold-low is used to set the RMS thresholds for burst detection. Normally these values should be in the range from 0.0 to 1.0 since this is the range normally produced by GNU radio sources.

Options:

-i, --input

gnuradio iq sample file (written by a file sink). If omitted, the samples will be read from stdin.

-o, --output

extracted/recorded and (optionally) zero-padded iq samples from input. If omitted, the output will be written to stdout.

-r, --record

Record burst from input and write to output. If this option is omitted, burst will only be detected and reported (see description above)

-n, --record-burst-nbr

The burst number (starting from zero) in input to record. The program will terminate as soon as the burst has been written to output

-b, --record-pre-burst-len

The number of samples before the detected burst start that should be added to the recording.

-a --record-post-burst-len

The number of samples after the detected burst end that should be added to the recording.

-l, --outfile-length

The length in samples of the output file. If the length of the extracted burst is less than this value, the output will be zero-padded. If the length of the extracted burst is greater than this value, the output will be truncated.

-u, --detection-threshold-high

High power burst detection threshold. If the average RMS value of the input exceeds this value, a start-of-burst is detected

-w, --detection-threshold-low

Low power burst detection threshold. If the average RMS value of the input drops below this value, an end-of-burst is detected.

-N, --detection-averaging-len

The number of samples that will be used when calculating the Moving Average RMS value of the input.