Impulse Noise And Doppler Shift Estimation Method In Underwater Acoustic Communication

In recent years,with the development of marine resources and national defense,how to provide high-speed and high-reliability information transmission in underwater environment has become a hot research field in underwater acoustic communication.However,underwater acoustic communication faces many challenges,inter-symbol interference caused by multipath transmission,impulse noise interference caused by complex underwater acoustic environment,and Doppler shift caused by relative motion between transmitter and receiver,and also seawater fluctuations,which affect the performance of underwater acoustic communication systems.In particular,as the speed of sound is much lower than the speed of light,the above problems have a much greater impact on underwater acoustic communication systems than terrestrial wireless communication systems.Although Orthogonal Frequency Division Multiplexing(OFDM)can effectively solve the inter-symbol interference caused by multipath channels,when the impulse noise and Doppler frequency shift exist,it not only reduces the signal-to-noise ratio on each OFDM subcarrier,but also causing subcarrier interference,therefore degrade the performance of the OFDM system.This thesis focuses on the impulse noise and Doppler frequency shift problems in underwater acoustic OFDM communication system.The main work is as follows:Aiming at the problem of impulse noise interference in OFDM underwater acoustic communication system,an impulse noise suppression method based on regularized threshold iteration is proposed.Firstly,a hydro acoustic communication system model is established.Then by constructing an empty subcarrier matrix and using sparse characteristics of impulse noise in the time domain,an optimization problem for estimating impulse noise is constructed.In order to solve this nonconvex problem,regularization technique is adopted and the threshold iterative method is proposed to estimate the impulse noise.Simulation results show that the performance of the proposed method is better than that of the clipping method,orthogonal matching pursuit method,and least squares method.Aiming at impulse noise and Doppler shift coexistence in the OFDM underwater acoustic communication system,an alternating iteration implementation method of impulse noise and Doppler shift is proposed.This method is implemented in two steps.In the first step,suppose the initial frequency shift is zero,the impulse noise is extracted from the received signal by the regularized threshold iterative method based on the compressed sensing.In the second step,based on the estimated impulse noise,the Doppler shift is estimated by minimizing energy on the null subcarriers.In order to increase the performance,the above processing can be realized by multiple alternating iterations between the two steps until satisfying the stop condition.Computer simulation results show that the proposed method has better performance than that based on only impulse noise suppression or Doppler shift compensation?...