Doppler Scale Estimation For Underwater Acoustic Communications Using Dual Zadoff-chu Sequences And Experiment

With the increase of ocean exploration activities,the demand for underwater wireless information transmission is also increasing rapidly.At present,the commonly used underwater wireless information transmission technologies include underwater acoustic communication,underwater optical communication and underwater electromagnetic wave communication.Among them,underwater acoustic communication is the only form of communication that can transmit information for a long distance underwater.Its own technical characteristics and unique advantages make it one of the important technologies in marine resources development and marine environment stereo monitoring system.Underwater acoustic communications have been broadly studied and applied in recent years.However,underwater acoustic communication faces many challenges.The reason lies in the complexity of underwater acoustic channel.As one of the most complex wireless channels in nature,underwater acoustic channel has a series of characteristics,such as small transmission bandwidth,serious multipath effect,serious Doppler effect,complex environmental noise components and long time delay propagation,which seriously limit the quality of underwater acoustic communication.To achieve better performance of underwater acoustic information transmission,we need to design a specific preamble according to the characteristics of the underwater acoustic channel.By designing appropriate structure and parameters,the preamble can obtain channel information,which is conducive to the correct recovery of information.Doppler effect is ubiquitous in underwater acoustic channel,because there is usually relative motion between transceivers.The length of the received signal will be compressed or expanded to a certain extent compared with the length of the transmitted signal.Therefore,before processing the received signal,it is necessary to accurately estimate the Doppler factor of the underwater acoustic channel in order to recover the signal waveform.How to accurately estimate the Doppler factor of the underwater acoustic channel has become an important research direction in underwater acoustic communication,which is also the focus of this paper.In fact,many research institutes have proposed various Doppler estimation schemes for underwater acoustic channels.However,the existing underwater acoustic channel Doppler estimation schemes usually do not introduce specific research scenarios,or can not estimate the Doppler factor in real time,and some schemes have a high computation.Therefore,this paper studies the Doppler estimation of underwater acoustic channel in the presence of relative motion of transceiver,and proposes a new estimation scheme.Firstly,the concept and characteristics of Zadoff-Chu sequence are introduced.After that,the Dual-ZC sequence designed in this paper is introduced,and the structure and parameters of the Dual-ZC sequence are designed to enable it to have effective resistance to multipath interference;a SSML underwater acoustic channel model is established according to the research scenario of relative motion of transceiver;on the basis of Dual-ZC sequence and SSML channel model,the receiver signal processing algorithm is designed,which can achieve higher estimation accuracy while maintaining less computation.The performance of Dual-ZC sequence and the effectiveness of signal processing algorithm are verified by computer simulations.To verify the feasibility of Doppler estimation scheme for underwater acoustic channel,an AUV is designed and manufactured as a mobile platform for underwater acoustic communications experiment.The AUV has eight propellers and can realize agile motion underwater,AUV will be equipped with underwater acoustic communication equipment,and Doppler effect can be produced by controlling the speed of the AUV.The various velocity represents different Doppler factors.AUV function test was carried out in a laboratory water tank and school towing tank.The test results show that the AUV can be used as a perfect mobile test platform for underwater acoustic communication.Finally,we have carried out three experiments of underwater acoustic channel Doppler estimation schemes under three underwater acoustic environments:pond experiment,lake experiment,and ocean channel data.The experimental results verify the feasibility of the proposed Doppler estimation scheme for underwater acoustic channel,which can be applied to underwater acoustic communication system.