Efficient Doppler estimation method based on pilot chirp Z transformation for base-band OFDM underwater acoustic communication

In OFDM (Orthogonal Frequency Division Multiplexing) underwater acoustic communication, when the transmitter and the receiver have a relative acceleration, the traditional Doppler shift estimation method has big error. Our efficient estimation method can, we believe, suppress greatly this error. Section 1 of the full paper deals with OFDM base-band transmission for underwater acoustic communication. Sections 2 and 3 select pilot frequency signals in accordance with the interpolation method explained in Fig. 2. Using eqs. (11), (12) and (13) in section 3 can estimate the Doppler shift with high precision by the process of Chirp Z transformation for each OFDM symbol. The simulation results, shown in Figs. 4 through 9, indicate preliminarily that: (1) when the speed of the transmitter relative to that of the receiver is less than 20 m/s, the estimation error of our Doppler shift method is less than 3.6 × 10^-6, which is two orders of magnitude smaller than that of the traditional method; (2) the estimation error of our Doppler shift method is also less than 3.6 × 10^-6 when the initial speed of the transmitter relative to that of the receiver is less than 20 m/s and the relative acceleration is less than 1.4 m/s²; (3) the OFDM system's performance curve of error bit rate validates that our method is useful for reception signal's estimation and compensation when there is a relative acceleration.