Difference between revisions of "Fast Auto-correlation"
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Auto-correlation of a W-CDMA downlink channel, showing the pilot channel's radio frames repeating every 10ms: | Auto-correlation of a W-CDMA downlink channel, showing the pilot channel's radio frames repeating every 10ms: | ||
| − | [[File:CDMA_FAC.png|800px]] | + | [[File:W-CDMA_FAC.png|800px]] |
In GRC, the blocks as such: | In GRC, the blocks as such: | ||
| − | [[File:GRC-FAC.png] | + | [[File:GRC-FAC.png]] |
| − | ] | ||
Revision as of 21:29, 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 block definitions so that it could be used 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:
