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What is the difference between 4QAM and QPSK and what is I and Q components?

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sinnadyr

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I am writing a thesis on using G3-PLC for power line communications, whereas the G3 standard uses D/QPSK modulation. What I have figured out so far is that both 4QAM and QPSK appearently produces the same waveform, but are they the same matematically?

In a QPSK constellation, are the mapping points at 45, 125, 225 and 315 degrees while the 4QAM is at 0, 90, 180 and 270?

I also struggle to understand the I/Q components of such a constellation diagram. What does "inphase" and "quadrature-phase" actually mean? Is it only other words for real and imaginary part for this type of usage?


Thank you.
 

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