Research And Algorithm Optimization Of Wideband Doppler Estimation And Compensation For Underwater Acoustic OFDM

In recent years,orthogonal frequency division multiplexing(OFDM)is widely used in underwater acoustic(UWA)communication as a high-speed communication technology.However,due to the limited available bandwidth and low propagation speed of acoustic wave,underwater acoustic communication suffered serious Doppler effect,which causes different Doppler frequency offset for different frequency components,so it is called wideband Doppler,which is usually described by Doppler scale factor.Therefore,how to solve the wideband Doppler effect is the key factor to affect the performance of UWA OFDM system.The research content and work are as follows(1)A high-precision wideband Doppler estimation algorithm combined with interpolation is proposed in this paper to improve the estimation accuracy of traditional method based on CP-OFDM autocorrelation,whose accuracy decreases due to the estimation grid.Firstly,the closed-form solution of CP-OFDM symbol autocorrelation is derived in this paper.Then based on the closed-form solution and Taylor formula,a variety of interpolation algorithms for different oversampling factors are proposed Simulation and sea trial data show that the proposed Method 1 and Method 2 achieve the best estimation performance in the case of oversampling and baseband sampling rate respectively.The running time of the proposed algorithm on the embedded digital signal processing(DSP)platform shows that the proposed algorithm can significantly improve the estimation accuracy of the traditional Doppler estimation algorithm based CP-OFDM autocorrelation with only a small amount of extra complexity.(2)In this paper,the wideband Doppler compensation algorithms based on high dimension FFT and interpolation is proposed in order to eliminate the rounding error introduced by the frequency domain index calculation in traditional FFT based Doppler compensation algorithm.The OFDM wideband Doppler compensation model in frequency domain is derived by Taylor formula.Then,the interpolation algorithm with high dimension FFT output is proposed based on this model.The simulation and sea trial data show that the performance of the proposed algorithm is better than that of the traditional FFT based algorithm.And compared with the benchmark of Chirp Z-transform(CZT),the proposed algorithm achieves almost the same bit error rate(BER)performance with only half complex multiplications.Both proposed algorithm and CZT based are implemented on DSP platform,and the running time of the proposed algorithm is lower than CZT based algorithm significantly with the similar BER performance.(3)The joint channel-estimation-and-decoding can achieve better performance than the traditional decoupled receiver.In this paper,the message passing receiver for cluster sparse channel is applied to UWA channel.The sea trial data show that the message passing receiver can combined with the proposed Doppler estimation and compensation algorithm in this paper,and obtain better BER performance than the traditional Doppler processing method.