How can you correct the anticlockwise rotation that occurs in the received constellation of a QAM system?

My only idea is to compensate the delay with an advance but this is impossible since you would have to decode the message before receiving it.

  • $\begingroup$ The rotation is not generally counterclockwise. What you're looking for is phase synchronization, and there's very many ways you do that in practice. We don't know the context of your question, so I can really only recommend you look into that term, phase synchronization. $\endgroup$ – Marcus Müller Jan 11 '19 at 16:16
  • $\begingroup$ See this answer I gave previously on carrier recovery for QAM: dsp.stackexchange.com/questions/17297/… $\endgroup$ – Dan Boschen Oct 9 '19 at 2:52

If this represents the received signal where $a$ and $b$ are the real and imaginary parts respectively $s(t-\Delta) \approx [a \cos{(2\pi f_o \Delta)}-b \sin{(2 \pi f_o \Delta)}] \phi(t) \sqrt{2} \cos{(2 \pi f_o t)} + [b \cos{(2 \pi f_o \Delta)} + a \sin{(2 \pi f_o \Delta)}] \phi(t) \sqrt{2} \sin{(2 \pi f_o t)}$

one can see exactly how the signal has been rotated. Therefore the rotation can be countered by introducing a sine or cosine to counteract the delay.


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