The Research On Doppler Processing And Diversity Scheme Over Underwater Acoustic Channel

With more and more frequent human activities in the oceans, underwater acoustic communication, especially high-speed underwater acoustic communications are enormously demanded in whether military or civilian commercial areas. Underwater acoustic channel is both time-varying and space-varying, with the characterization of limited band, serve multi-path and Doppler Effect, which make the channel, especially the shallow water acoustic channel become the most complicated wireless channel.The main research in the current acoustic channel with long delay focuses on the two aspects: the research on the anti-fading technology on the time-varying characteristics of the underwater acoustic channels, and the research on the high data rate transmission efficient modulation technology in the narrowband underwater acoustic channel.This thesis describes the common underwater acoustic channel model. Starting from the ray model of the sound field, eigenray search method is used to get parameters of underwater acoustic channels of the channel later in the simulation. This paper focuses on the process for the efficient transmission in the time-varying underwater acoustic multi-path channel and researches on the following two-level.Firstly, this thesis focuses on the how to eliminate the effect of the interference caused by the high value of Doppler factor in the band limited underwater acoustic channel. Based on the estimation of the channel impulse response, multipath channel of the underwater acoustic channel can be effectively separated. Digital offset compensation method in the frequency domain is used to obtain stable receiver performance. Then estimation and compensation methods of the wideband Doppler shift in the high Doppler factor of the characteristics are applied to underwater acoustic ZP-OFDM system. From the simulation results, the method has higher estimation accuracy and the compensation effect.This thesis also increase the modulation efficiency from the perspective of the initiative, focusing on the introduction of diversity, the transmitter codes, adaptive modulation and other technical solutions. By means of the comparison among these technologies, the performance characteristics of different technical solutions are detailed as well as in a real environment of applicability. Based on underwater acoustic channel characteristics, the performance of the diversity technologies, space-frequency coding and adaptive modulation code scheme are compared in the application of underwater acoustic communication, so as to improve the efficiency of acoustic communication system modulation.