Research On Adaptive Channel Estimation Technology For Underwater Acoustic Spread Spectrum Communication

The complex and changeable characteristics of underwater acoustic channels have brought many difficulties to long-distance communication,such as the Doppler Effect caused by the relative motion of communication nodes,complex multipath propagation and noise caused by special marine environments.In view of the multipath propagation phenomenon in underwater acoustic communication,spread spectrum communication has good resistance.At the same time,spread spectrum technology also has the advantages of reliable transmission at low signal-to-noise ratio and difficult interception.Therefore,this paper adopts hydroacoustic spread spectrum communication technology to improve the performance of the system by studying Doppler factor estimation compensation technology,multipath channel estimation technology,RAKE receiver technology and time reversal mirror technology,so as to ensure the stable and reliable operation of the system.In this paper,the basic characteristics of the underwater acoustic channel are analyzed,a basic model is established,and the influence of Doppler frequency shift phenomenon and multipath propagation phenomenon on performance in the communication process is analyzed.Secondly,the basic principles of underwater acoustic spread spectrum communication are studied,and the Effects of Doppler effect and multipath propagation on system performance are simulated.Aiming at the Doppler Effect caused by the relative motion of the transceiver in the process of underwater acoustic communication,the Doppler factor estimation algorithm based on matching filtering and the Doppler factor estimation algorithm of fractional Fourier transform are studied,and the performance of the algorithm is analyzed and compared.After Doppler compensation,aiming at the multipath propagation problem in the process of underwater acoustic communication,the minimum mean square channel equalization algorithm and the compressed sensing channel estimation algorithm are introduced respectively,and their performance is simulated and verified.Finally,on this basis,an improved adaptive channel estimation algorithm combining minimum mean square channel equalization,wavelet transform noise estimation and compressed sensing channel estimation is proposed,and the performance of this algorithm is compared with the traditional channel estimation algorithm.After the adaptive channel estimation of the channel,the multipath information of the channel can be obtained,and different means can be used to achieve better communication performance.Firstly,the RAKE receiver is studied,and the influence of different merging methods and different receiver types on system performance is analyzed.Secondly,the basic principle of time reversal mirror is analyzed,and the advantages of time reversal mirror are summarized.Finally,the RAKE receiver based on the time reversal mirror is studied,and in this part,the adaptive channel estimation technology is first used to estimate the channel information of the received signal for the first time,and the time inversion processing of this channel is performed to obtain the time inverse channel,and then the adaptive channel estimation algorithm is used to estimate the final channel,and the RAKE receiver is used to process it to improve the performance of the communication system.