Speaking of I/Q imbalance

Has there ever been any discussion of adding an I/Q imbalance correction
block into the Rx chain in the FPGA image on the USRP/USRP2? On past
systems that I’ve worked on, the calibration procedure to get this
imbalance
reduced can take quite a long time and still only produces moderately
improved results. An alternate approach, of course, is simply to fix it
digitally. One example write-up of this can be found here:

http://fargus.naapo.org/~rchilders/swe_argus_pubs/iqbal.pdf

I know that Bob McGwier has also been doing a bunch of work recently to
tackle this problem, and would be interested if any additional details
of
this work are available yet.

Anyway, we’ve tested the aforementioned paper’s scheme, and it works
quite
well. Its really just a couple of complex multiplies, once you have the
correction parameters determined (which will be frequency and/or
hardware
dependent).

If there is any interest here, we’d be happy to submit a patch to the
FPGA
codebase to add this capability in. And for people who don’t need it,
the
block can simply be bypassed.

Comments welcome…

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