Research On Mobile Underwater Acoustic Communication Based On Hyperbolic Frequency Modulation Signal

With the rapid development of human marine activities and the rapid development of mobile platforms such as Autonomous Underwater Vehicles(AUVs),there is a growing demand for underwater wireless communication.The Underwater Acoustic Channel,as one of the most complex wireless channels,has.the characteristics of non-negligible Doppler effect and time-varying multipath propagation effect in mobile scenario.Nowadays the research of underwater acoustic communication focuses on the direction of channel equalization,multi-carrier modulation,spatial modulation and so on,but the incoherent techniques of underwater acoustic communication based on Hyperbolic Frequency Modulation(HFM)signal have the advantages of simple realization,stable and reliable communication,low power consumption and so on,and is suitable for being used in AUV mobile communication scenario.This paper mainly focuses on the key technologies of mobile underwater acoustic communication based on HFM signal,including Doppler scale estimation and modulation/demodulation technology.In this paper,the characteristics of Underwater Acoustic Channel are introduced firstly,especially the deterioration of the channel condition caused by the mobile scenario.Then the underwater acoustic channel of the field experiment is modeled using Bellhop Ray tracing program for subsequent simulation of the underwater acoustic communication system.Then we study the Doppler estimation and timing synchronization method based on up-down HFM signals.The expression of Main Ridge of Ambiguity Function of HFM signal is deduced at first,then we come up with the expression of the estimated Doppler factor based on the HFM-signal-based up-down method.Finally,a new Doppler estimation method is proposed,which is called "up-down HFM joint M sequence method".By comparing with two kinds of commonly used Doppler estimation methods,the proposed method has the advantages of low computational cost and support online realtime processing.We study the modulation and demodulation technology based on HFM signal for mobile underwater acoustic communication as the next step.Combining Chirp Modulation(CM),Frequency Hopping(FH)and Pattern Time Delay Shift Coding(PDS),a method which can effectively combat Doppler spreading effect?noise interference and strong multipath interference is proposed,called as PDS-FH-CM method,and the stability and reliability of this method is verified through simulation.Finally,this paper introduces the field experiments of mobile underwater acoustic communication.The Doppler estimation experiment based on AUV platform is introduced at first.By comparing the relative velocity measured by the sensor mounted in the AUV and the Doppler velocity estimated by the up-down HFM method,the validity of the up-down method is proved.This paper also introduces the experiments using moving boats designed on the lake and sea,and the effectiveness of the proposed modulation method is verified by calculating the bit error rate of the experiments.The experimental results are in good agreement with the simulation results.