Application of Modified Luise and Reggiannini Method for Blind Estimation of Frequency Offset for QAM Signals

A closed-form method for blind estimation of frequency offset for signals with quadrature amplitude modulation (QAM) is proposed. The method is based on a known Luise & Reggianini method intended for harmonic signal frequency estimation. To adapt to the properties of QAM signals, two changes were made to the method. First of all, the required correlation functions are calculated with a two-dimensional weighting function that depends on the magnitudes of two signal samples. Then, when summing the correlation functions, their magnitudes are set to a unit value. Optimization of the weighting function is carried out by training in batch mode using generated sequences of signal samples. The results of computer simulation confirmed the efficiency of the proposed method and showed a noticeable gain due to normalization of the magnitudes of correlation functions.