Phase/Frequency Control Method Using Least Mean Squares (LMS) for M-QAM Demodulator

Abstract

This paper reports a new scheme of carrier recovery for multilevel QAM. First, we investigate the conventional LMS algorithm with the error estimation function. To achieve quick carrier recovery and simplify the circuit, apply the conventional LMS algorithm not only to the phase domain but also to the frequency domain. By defining the estimated frequency error to be the variation of the coefficient of phase compensation in the phase domain, we introduce the new algorithm. We apply this new algorithm to the carrier recovery circuit of a 64 QAM demodulator in an offset frequency condition. The computer simulation results show that the performance of the new algorithm is superior to that of the conventional LMS algorithm in terms of the recovery time and the enhanced range of the offset correction up to ± 1/2 symbol frequency.