A wideband carrier-recovery system for multilevel QAM signals

A decision-directed carrier-recovery technique for coherent demodulation of quadrature amplitude modulated (QAM) signals is proposed. This system adaptively tracks both the carrier frequency and phase of the received QAM signal's modulated carrier. The acquisition time of the proposed system is shown to be faster than that of conventional carrier-recovery schemes, especially when the initial carrier-frequency offset is relatively large, i.e. beyond a small fraction of the symbol rate. Also, the proposed method has a wider acquisition range compared to conventional techniques.