Difference between revisions of "Fast Auto-correlation"
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== Intro == | == Intro == | ||
| − | Frank of [http://sites.google.com/site/radiorausch/ | + | Frank of [http://sites.google.com/site/radiorausch/ radiorausch fame] put together [http://sites.google.com/site/radiorausch/USRPFastAutocorrelation.html an excellent page] (and some code) on performing real-time auto-correlation with [http://gnuradio.org/ GNU Radio] and the [http://ettus.com/products USRP]. |
Unfortunately the code no longer works with the new version of GNU Radio, so I upgraded it and wrote some XML block definitions enabling its use as a graphical sink in [http://gnuradio.org/redmine/projects/gnuradio/wiki/GNURadioCompanion GRC] (GNU Radio Companion). | Unfortunately the code no longer works with the new version of GNU Radio, so I upgraded it and wrote some XML block definitions enabling its use as a graphical sink in [http://gnuradio.org/redmine/projects/gnuradio/wiki/GNURadioCompanion GRC] (GNU Radio Companion). | ||
Revision as of 23:00, 18 July 2011
Intro
Frank of radiorausch fame put together an excellent page (and some code) on performing real-time auto-correlation with GNU Radio and the USRP.
Unfortunately the code no longer works with the new version of GNU Radio, so I upgraded it and wrote some XML block definitions enabling its use as a graphical sink in GRC (GNU Radio Companion).
Please refer to Frank's page for the gory details. Suffice to say that his FAC (Fast Auto-Correlation) implementation exploits the Wiener Khinchin theorem, which in this context essentially means that if you take the FFT of the power spectrum of a signal (i.e. two FFTs), "we have a particularly fast way of calculating auto-correlations" - Frank.
GRC Block
Auto-correlation of a W-CDMA downlink channel, showing the pilot channel's radio frames repeating every 10ms:
In GRC, the FAC sink appears as such:
Download
Make sure you either place the Python code where Python will find it, or in a location that you add to your PYTHONPATH environment variable.
The XML block definition needs to be found by GRC. You can place it:
- in ~/.grc_gnuradio
- alongside all the other blocks (usually /usr/local/share/gnuradio/grc/blocks)
- elsewhere (see GRC documentation about other options)
Please let me know how this block works for you!
