## QAM detection

#### 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. |

#### The output of each demodulator is a baseband multi-level symbol set. Ideally this should undergo matched filtering for optimum performance in noise, before being passed through a bank of comparators to determine the level from each demodulator at the sampling instant, and hence decode the corresponding bit pattern.