Improved Doppler Scale Estimation Based on Autocorrelation Function for Underwater Cyclic Prefix-Orthogonal Frequency Division Multiplexing Preamble

An enhanced Doppler estimation method that utilizes the phase of the autocorrelation function (ACF) is proposed in this study. The resolution of the Doppler scale estimation for the conventional autocorrelation method depends on the sampling rate of the received signal. By utilizing the phase of autocorrelation as a measurement, higher Doppler estimation accuracy without raising the sampling rate is achieved. However, the Doppler estimation range is limited to the induced phase ambiguity. A novel phase unwrapping method integrated with the Doppler scale factor is addressed to eliminate the phase ambiguity. The transmit signal considered in this study is cyclic prefix-orthogonal frequency division multiplexing preamble which satisfies the cyclic autocorrelation property, and the channel is modeled as each propagation path having a constant Doppler factor. Simulation results reveal that the proposed method achieves a performance gain of 10 dB compared with the conventional autocorrelation method and can be employed to obtain a large dynamic Doppler estimation range.