This project is part of the ptp-sim project. See the ptp-sim project page for more information. There is also the ptp-sim discussion forum for further discussions.
The library libPLN provides an implementation for the efficient generation of Powerlaw Noise (PLN).
PLN is a type of noise where the power spectral density (PSD) of the fractional frequency deviation (FFD) is proportional to f^alpha. This type of noise is commonly found in oscillators. See IEEE 1139 [1] for details on this topic. Typical values of alpha for quartz oscillators are
- Random walk noise: alpha = -2
- Flicker Frequency Modulation: alpha = -1
- White Frequency Modulation: alpha = 0
- Flicker Phase Modulation: alpha = 1
- White Phase Modulation: alpha = 2
PLN is generated by libPLN by filtering white noise with a special filter, using one of two methods:
- the method as described by Kasdin and Walter in [2]
- or a with recursive filter (availabled only for the noise classes random walk, white FM and white PM)
[1] IEEE Std 1139-2008: IEEE Standard Definitions of Physical Quantities for Fundamental Frequency and Time Metrology -- Random Instabilities
[2] N.Jeremy Kasdin and Todd Walter, Discrete Simulation of Powerlaw Noise, 1992
The main purpose for libPLN is the efficient generation of realistic noise in discrete event simulation (DES), for simulations of the Precision Time Protocol (PTP). For this purpose it supports not only the generation of continously sampled noise data, but also the estimation of noise values in the simulated future.
The current version of this library can be found on the project's Github site. LibPLN has been developed as part of the following master thesis:
Wolfgang Wallner, Simulation of Time-synchronized Networks using IEEE 1588-2008, 2016, Vienna University of Technology
Persistent URL: https://resolver.obvsg.at/urn:nbn:at:at-ubtuw:1-3908
This thesis contains an in-depth description on the various design decitions of the library.
The most important project directories are the following:
src: the source code for the libPLN libraryDocumentation: various documentation like Doxygen files and UML diagramsTests: a few simple tests mainly to catch regressionsDemos: a few simple demo programs to demonstrate the usage of libPLNExamples: implementations of simulated example oscillators
The demo programs come with their own readme documents in the respective directories.
This is a simple demo program that shows how to request time deviation values from one of the provided example oscillators, and how the library behaves for different requests.
This is a command line tool that uses libPLN to implement the simulation of continously sampled time deviation values. For details on its usage, see its Readme and Manual documents. An example for a generated noise vector is shown in the following image:
LibPLN also comes with implementations of example oscillators found in published literature.
This is an implementation of an oscillator with an Allan Deviation similar as the one given in:
A Novel, High Resolution Oscillator Model for DES Systems
Georg Gaderer, et al
Proceedings of the Frequency Control Symposium, 2008
This is an implementation of an oscillator with an Allan Deviation similar as the one given in:
The Accuracy and Stability of Quartz Watches
Michael Lombardi
Horological Journal, February 2008
The documentation files for this project are written in Markdown (line ending *.md). They can be either read in a text editor, are converted to HTML using the markdown utility.
LibPLN makes heavy use of other open source projects. We would like to thank the respective authors for publishing their projects! The used projects are:
-
FFTW: the Fastest Fourier Transform in the West http://www.fftw.org/
-
C++ Bricks interface for FFTW https://gitorious.org/cpp-bricks
-
Spline: a cubic spline implementation in C++ http://kluge.in-chemnitz.de/opensource/spline/
-
Numeric tricks https://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
This project is licensed under the GPLv3 license. See the COPYING file for details.
Please visit the ptp-sim discussion forum for further discussions.