Research On The Key Technologies Of Underwater Acoustic Single-Carrier Synchronization And Frequency Domain Equalization

With the development of society,underwater resources development and underwater military activities have more and more attention,in the process of underwater activities,reliable and stable means of communication are very necessary.The current underwater acoustic communication technology is Orthogonal Frequency Division Multiplexing（OFDM）technology,compared with Orthogonal Frequency Division Multiplexing technology,Single Carrier Frequency Domain Equalization（SC-FDE）technology has the advantage of being insensitive to frequency offset and low peak ratio,so SC-FDE has become an important research direction of underwater acoustic communication.In Single Carrier Frequency Domain Equalization system,accurate time synchronization and frequency synchronization of signals is an important prerequisite for complete information transmission.At the same time,the complex information of underwater acoustic channels is mutable,so achieving complete information transmission requires accurate channel estimation.However,traditional channel estimation techniques have shortcomings of high system overhead and low accuracy.Therefore,designing simultaneous techniques and channel estimation techniques with better performance is of great value.Focusing on the simultaneous techniques and channel estimation of SC-FDE system which is in underwater channel,the common algorithms are analyzed and the new algorithms are verified by simulations.Study on synchronization technology for the SC-FDE system.Using the correlation of the training sequence,aiming at the shortcomings of traditional timing synchronization techniques such as peak platform effect,sidelobe interference,proposing an improved combination structure based on training sequences.According to the correlation of Zadoff-Chu（ZC）sequences,this sequence is used as a training sequence,a new structure and a combination of multiple metric functions is be used.Genetic algorithm is used to optimize and select the composite structure,producing a new structure which sharpens the main lobe peak of the metric function,eliminates the peak platform,and suppresses side lobe interference.On the basis of timing synchronization,according to the characteristics of the synchronization sequence,the decimal frequency bias estimation in the time domain according to the phase difference of the same sequence,and the integer frequency bias estimation using the cyclic displacement in the frequency domain,it improves the performance of frequency deviation estimation.The simulation results show that the improved timing synchronization algorithm can improve the performance of about 10d B compared with other algorithms.The performance of the frequency deviation estimation algorithm proposed improves by 5d B compared with other algorithms,the synchronization performance of the system has be improved.Study on the channel estimation techniques for the SC-FDE systems.For the sparse nature of underwater channels,the compressed sensing theory is used in channel estimation.Aiming at the shortcomings of the compressed sensing reconstruction algorithm which needs to know the channel sparsity and low reconstruction accuracy,the sparsity was estimated in advance,it reduces the dependence of reconstruction algorithms on sparsity.Dynamic threshold screening mechanisms and atomic backtracking mechanism are adopted,which improving reconstruction performance of reconstruction algorithms.The results of the simulation show,when SNR is 30,the minimum mean square error of the new algorithm is 9.868×10^-5,the LS algorithm and the OMP algorithm are 1.009×10^-3and 2.135×10^-4.The results prove that the improved algorithm has a better channel estimation performance.