QAM can be decoded using coherent or differentially coherent
detection just as for PSK systems. We shall concern ourselves here only with
true coherent detection. Details of differential detection systems can be found in Proakis (1989). Just as for QPSK, a QAM demodulator requires
the recovery of quadrature carriers in the receiver. Very similar Nth
power carrier recovery circuits can be used, although the problem of dealing with phase ambiguity in the recovered carrier is greatly
complicated by the presence of the amplitude component of the data symbols. |
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