Research On Doppler Estimation And Compensation Technique For OFDM Underwater Acoustic Communication

In recent years,with the attention of various countries to ocean development strategy,underwater acoustic communication gets more and more attention,and develops towards high speed,mobility and networking.Affected by adverse ocean environment,underwater acoustic communication has the characteristics of high latency,low speed and high bit error rate.Orthogonal frequency division multiplexing(OFDM)is a modulation method with high frequency band utilization,and has been widely used in underwater acoustic communication.In this paper,we will study the Doppler estimation and compensation of OFDM in underwater acoustic communication.The main work is divided into the following aspects.Firstly,the underwater acoustic OFDM system has been analyzed and modeled.On the basis of the OFDM principle,advantages and defects,the key technology of OFDM underwater acoustic communication system was put forward,the influence of guard interval and cyclic prefix,the channel encoding and decoding technology and their effect on the system are discussed in detail.Then,the parameter selection and system design of OFDM system in underwater acoustic channel environment are given.The performance comparison of the system under different conditions is analyzed by simulation,and the effectiveness is verified.Secondly,the underwater environment and its modeling methods were studied,the main characteristics of the underwater acoustic channel and its influence on underwater communication were analyzed.The underwater acoustic channel modeling based on ray theory and improved Gauss beam theory.A n underwater acoustic channel simulation tool BELLHOP is introduced,and the channel model in fixed environment is established by using it.On the basis of it,a method of building the time-varying channel model is put forward,which takes account of time variation and Doppler characteristics of underwater acoustic channel,and paves th e way for further research.Finally,the Doppler frequency shift of OFDM system caused by time-varying underwater acoustic channel is studied.The influence on underwater acoustic OFDM system is analyzed and a compensation scheme is proposed.Based on the analysis of the existing compensation methods,two wideband Doppler frequency shift estimation methods and three narrowband Doppler frequency shift estimation methods are summarized.In view of the shortcomings of the existing methods,an improved scheme for Doppler estimation and compensation is proposed.The estimation is carried out by constructing different cost function,and the simulation analysis of proposed method is carried out.The research and analysis shows that the proposed Doppler estimation and compensation method can effectively deal with the Doppler effect of underwater acoustic channel,it enhances the performance of the existing estimation methods in estimation accuracy and range.The results of this research can be applied to underwater mobile OFDM communication system,which has certain theoretical significance and engineering value.