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Sorry to bring up painful memories :). I did some calculations to work
out frequency drift of the USRPs, and I wanted to know where I’m going
The crystals in the RFX 2400 are spec’ed at 50ppm error, which is to say
that the maximum frequency offset between the sender and receiver is
then 2 * 50 ppm * 2.462 GHz (802.11b Channel 11) = 246.2 kHz.
246.2 kHz sampled at 64 MHz is 246.2 kHz * 2pi / 64 MHz which is
approximately 0.02417 radians / sample.
At, say, DBPSK 250kbps, oversampled by a factor of 2, that means we
decimate by 128 (500 ksamples per second), to then get at most ~3.094
radians per sample drift.
With DBPSK this could flip all of our bits! Does that mean we in fact do
need to worry about the case where the complement of the access code is
detected? Is my understanding of the meaning of ppm error wrong? Does
the distribution we assume for the frequency offset make this
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