Large Frequency Offset Estimation for Digitally Modulated Signals in Low SNR Environment

There is a need, in the presence of large carrier frequency offset, to estimate the frequency offset by a fractionally sampled non-linear least square (NLLS) algorithm. In low signal-to-noise ratio(SNR) environment, the coarse estimate step will mainly determine the performance of the NLLS algorithm. This paper firstly extend the baud-rate sampled NLLS frequency offset estimator to the fractionally sampled scheme, then study the optimal second order statistic under different oversampling rate in the coarse estimate step for MSK type and PAM signals, whose frequency offset can be estimated in low SNR environment. The proposed algorithms outperforms the traditional NLLS algorithms in low SNR environment. Simulation results coroborrate the proposition.