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Blind carrier frequency offset estimation for QAM signals based on weighted 4th power of signal samples

The method is presented for blind frequency offset estimation for signals with quadrature amplitude modulation (QAM). The method is based on a circular harmonic expansion of log-likelihood function (LLF). By retaining only the most significant term in this series a radius-weighted version of popular 4th power frequency estimation algorithm is obtained. This approach leads to notable improvement of the estimation quality. Computer simulation was performed with 16-QAM and 32-QAM signals, the results justified the advantages of the suggested method. It was also shown that using fixed (SNR-independent) weighting functions does not lead to any notable performance loss.