Difference between revisions of "Fast Auto-correlation"
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Frank of [http://sites.google.com/site/radiorausch/ radiorauch 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]. | Frank of [http://sites.google.com/site/radiorausch/ radiorauch 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 block definitions | + | 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). |
| − | 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. | + | Please refer to Frank's page for the gory details. Suffice to say that his FAC (Fast Auto-Correlation) implementation exploits the [http://en.wikipedia.org/wiki/Wiener%E2%80%93Khinchin_theorem Wiener Khinchin theorem], which in this context essentially means that if you take the [http://en.wikipedia.org/wiki/Fast_Fourier_transform 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 == | == GRC Block == | ||
Revision as of 21:32, 18 July 2011
Intro
Frank of radiorauch 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 blocks as such:
