Doppler Scale Estimation For Underwater Acoustic Communications Using Zadoff-Chu Sequences

With the increasing attention of the world to the ocean,more and more researchers join the development of marine science and technology.Underwater wireless communication is just one of the most important technologies.Underwater acoustic communication,as the only effective long-distance wireless communication method underwater,has been widely used.However,the complex underwater environment and the characteristics of acoustic wave make the underwater acoustic communication face many challenges.Underwater acoustic channel is recognized as one of the most complicated and challenging wireless channels.Narrow bandwidth,multi-path effect,Doppler effect and various kinds of noise all seriously affect the efficiency and quality of underwater acoustic communication.In the process of underwater acoustic communication,the Doppler effect will have a serious impact on the received signal at the receiver,which will shrink or expand in the time domain,seriously affect the recovery of the signal,and even cause the communication system to break down.Therefore,for the Doppler effect in underwater acoustic communication,it is necessary to put forward corresponding solutions so as to recover the data information correctly at the receiver.In the underwater acoustic communication system,the transmitter usually sends the data signal together with the preamble,and the receiver uses the known characteristics of the preamble to realize the channel parameter estimation.Therefore,the key to realize the Doppler scale estimation is to choose the appropriate preamble and design a reasonable Doppler estimation algorithm.Zadoff-Chu sequence is a kind of polyphase code,which has good autocorrelation and cross-correlation characteristics,low PAPR and so on.Aiming at the Doppler effect in underwater acoustic channel,this paper designs two Doppler estimation schemes with different channel models,taking the Zadoff-Chu sequence as the preamble.First,a single-scale Doppler estimation scheme is proposed,which uses the matching tracking method to estimate the Doppler scaling factor for the single-scale single-lag underwater acoustic channel.The second is the multi-scale Doppler estimation scheme.Directed against the multi-scale multi-lag underwater acoustic channel,the Doppler scale estimation is transformed into a frequency analysis problem,using the shift multiplication characteristic of Zadoff-Chu sequences.Thus,the estimation problem is simplified.Then,an iterative algorithm for estimating the multi-path Doppler scaling factor is designed.Through MATLAB simulation,the characteristics of Zadoff-Chu sequences and the feasibility of the proposed Doppler scale estimation schemes are verified.In order to verify the practicability and application value of the proposed schemes,we built the experimental platform of autonomous underwater vehicle(AUV),and completed the underwater long-distance wireless real-time control of the AUV,by integrating the existing underwater acoustic communication module and AUV.The Doppler effect is generated by the movement of AUV.Different relative velocities can represent different Doppler scaling factors.Finally,the Doppler estimation schemes proposed in this paper are tested on AUV and WATERMARK platforms,which verifies the feasibility and practicability to a certain extent.