A new carrier regeneration scheme for QAM signals

Customary processes for regenerating the carrier of a QAM (quadrature amplitude modulation) signal utilize the sampled receive signal in the vicinity of the nominal states of the state plane. Thus, once synchronization has occurred, good control action in the vicinity of the synchronization point is achieved. However, for higher-level QAM signals the synchronization process is not perfect. The author proposes a method in which the information contained in the amplitude and the relative phase position of the sampled signal values is used to calculate the most probable phase deviation of the local carrier signal in relation to the transmitted carrier signal. This provides better acquisition characteristics without impairing the good tracking characteristics obtained with other methods. Computer simulations suggest that relatively quick and secure synchronization will be achieved with higher-level QAM systems