Research On Single Carrier Frequency Domain Equalization In Underwater Acoustic Communications

Underwater acoustic communications and networking technologies are widely used in underwater vehicles,manned diving operations,and marine environment detection.How to realize a high-speed and robust underwater communication system is a current research hotspot in currently.Single carrier communication is one of the important technologies suitable for underwater acoustic communication.In order to meet the needs of high-speed communication between underwater equipment nodes,a suitable underwater acoustic single carrier frequency domain(SC-FDE)balanced communication system is designed in this dissertation.Firstly,based on the background of shallow sea acoustic communication,the dissertation models and simulates a typical underwater acoustic channel model,and performs a performance simulation of SC-FDE under the channel model,which provides a reference for communication performance in actual environments.Aiming at the high processing complexity of time domain equalization,frequency domain equalization is proposed to solve this problem.The transmitting and receiving structure of the underwater acoustic SC-FDE system is designed,which provides a new solution for underwater equipment communication.To make the communication system with high overall performance,the dissertation conducts detailed research and design for five key steps of the frequency domain equalization receiver.First,the dissertation addresses the problem of equalization algorithms in frequency domain equalization by studying linear equalizer under the zero-forcing(LE-ZF)criterion and the minimum mean square(LE-MMSE)criterion,and nonlinear frequency-domain equalization of hybrid-decision feedback equalizer(H-DFE)and analyzes the conditions for using different frequency domain equalization algorithms in different scenarios.Second,for the problems that the traditional recursive least squares(RLS)channel estimation algorithm is influenced by the filter parameters and the zero-valued taps are non-zero,the sparse channel estimation algorithm with orthogonal matching pursuit(OMP)is studied to further improve the system performance of frequency domain equalization.Third,for the synchronization part of the frequency domain equalization system,the timing deviation problem in frequency domain equalization is studied to reduce the performance loss in the presence of timing errors.Fourth,for the estimation of the SNR parameter required by the equalizer,the effect of the SNR estimation on the equalization performance is studied,and the property that the equalizer coefficients are insensitive to the SNR estimation is obtained.Fifth,for the Doppler estimation problem in the frequency domain equalization system,the maximum Doppler tolerance of the frequency domain equalization is calculated by simulation;for the Doppler sensitivity problem of the frequency domain equalization,an improved autocorrelation-based Doppler estimation algorithm is studied to compensate the performance loss caused by Doppler.At the end of the dissertation,for the underwater acoustic communication system with array reception,a multi-array element receiving structure with SC-FDE is designed.Compared with single-channel frequency domain equalization,multi-channel frequency domain equalization reduces the impact of independent channel fading and effectively improves the performance of the communication system.The feasibility and effectiveness of the underwater acoustic SC-FDE communication system described in this dissertation in the actual mobile and high communication rate environment are verified by field test data processing.