Impulse Noise And Doppler Frequency Shift Processing Method In Underwater Acoustic Communication

Underwater acoustic communication is the main way to transmit information underwater.In the underwater acoustic environment,the channel delay spread characteristics are significant,and there is also a large amount of random,high-energy impulse noise.In order to mitigate the interference of impulsive noise,empty subcarriers are often added to the transmitted signal,which reduce band utilizationleads to the availability of Band resources are extremely limited.At the same time,the speed of sound is several orders of magnitude lower than the speed of light,which causes the Doppler frequency shift to cause more serious damage to underwater acoustic communication and greatly reduces the performance of underwater acoustic OFDM communication systems.For signal transmission,lower communication delay,cheaper communication cost,and stable communication quality have always been the goals pursued.Therefore,this thesis focuses on the estimation and compensation of impulse noise and Doppler frequency shift offset in underwater acoustic OFDM communication system.The main contributions are as follows:1? In the underwater acoustic communication environment,according to the sparse characteristics of impulse noise in the time domain,a method of impulse noise suppression based on compressed sensing theory is proposed.First,a discrete signal model is established for the underwater acoustic OFDM communication system,and then an improved impulse noise suppression algorithm is proposed based on the theory of compressed sensing,which relaxes the traditional NP-hard problem into a solvable convex problem.Compared with some existing algorithms,the proposed algorithm shows better performance.2?Since the interference of impulsive noise and Doppler frequency offset coexist in the underwater acoustic environment,according to the idea of subspace decomposition,a method of suppression compensation for impulse noise and Doppler frequency offset based on alternating iteration is proposed.This algorithm transforms the problem of estimating the position of impulsive noise on empty subcarriers into a problem of estimating the power spectrum in the subspace.After obtaining the estimated value of impulsive noise,the Doppler frequency offset of the signal is also obtained Furthermore,iterating alternately and finally suppressing interference at the receiving end Compared with the general method,the performance is greatly improved.3 ? Aiming at the problem of low carrier utilization in underwater acoustic communication,an impulse noise suppression algorithm based on BP neural network and least squares is proposed.This method first considers the position estimation of the impulsive noise of underwater acoustic communication in the time domain as a positioning problem,and then builds an algorithm based on the BP neural network.Then the least square algorithm is used to estimate the impulsive noise amplitude.The impulse noise is suppressed at the receiver side.Multiple signal transmissions are carried out in a stable communication environment,and the construction of the neural network can be used repeatedly,which reduces the energy consumption of the communication system to a certain extent.At the same time,when the amount of impulse noise increases,it only needs to increase the number of data groups participating in training without adding additional empty subcarriers,which greatly improves the bandwidth efficiency..