Research On The Key Technology Of AUV Acoustic Frequency-hopping FSK Communication

AUV(Autonomous Underwater Vehicle)is an important tool to explore and develop the ocean.Underwater acoustic communication technology plays a crucial role in the control and information interaction in AUV.However,the hightly dynamic doubly spread(i.e.multipath spread and Doppler spread)can cause performance degeneration of the AUV communication system in the underwater acoustic channel.In this paper,joint frame synchronization,Doppler estimation and compensation technique,transmission of AUV data synchronization protocol and single element/array based channel shorterning technology are employed to solve the practical problems in underwater acoustic channel.Firstly,the difficulties of AUV underwater acoustic communication technology are expounded according to the practical demands of AUV underwater acoustic communication.Then,the development and status of existing AUV underwater acoustic communication technology are summarized.The research about the key technology of AUV is conducted according to the actual technical requirement of AUV underwater acoustic communication system.Secondly,we carried out experimental and theoretical research aiming at solving the problems of real-time requirements and estimation,tracking and compensation for time-varying Doppler in the underwater acoustic communication systems.Theory researches are conducted as follows:(1)the design of frame structure which is based on a joint frame synchronization and Doppler estimation and compensation for AUV frequency hopping underwater acoustic communication system;(2)the frame synchronization technology which can adaptively adopt the environment;(3)the Doppler estimation technology based on pulse mutual association variance technology of initial frame synchronization estimation technology;(4)the symbol by symbol timing and Doppler tracking and compensation technology with a low computing complexity for real-time application under accelerated conditions.We also carried out the simulation and the lake experiments,experimental results show that when the communication rate is 160bps,the estimated value of speed error between the GPS and the pulse mutual association variance technology is-0.3m/s?0.3m/s when relative speed is 0?3 knots.Moreover,the bit-error rate after demodulation can be reduced from 20%to 5%by the Doppler compensation technology of low complexity linear interpolation.Therefore,bi-directional data transmission between the surface and the under water can be obtained with no bit-error rate after channel decodingThirdly,we carried out a study of synchronous data transmission protocol based on underwater acoustic communication link under the conditions of the movement between AUV and the platforms.Due to the limited bandwidth of underwater acoustic channel because of its frequency absorption,the two sides usually communicate in the same frequency band.In order to avoid communication conflicts,the technology of clock synchronization is required.Different from the synchronization technology of wireless sensor network on the land,there existences large propagation delays due to low acoustic sound speed.Moreover,the compromise on the accuracy of clock synchronization and the consumption of resources is also considered because of the unstability of acoustic communication and limited battery energy.Time Synchronization for High Latency(TSHL)clock synchronization protocol is the most suitable for the underwater network environment with two steps of clock synchronization.Nevertheless,the synchronization precision is ensured only when nodes are relatively static.Therefore,the relative movement of AUV and the the mother ship makes the round-trip propagation delay unequal during clock synchronization which can increase the error of clock synchronization.In this paper,we make some improvements on the TSHL clock synchronization protocol.We propose a dynamic clock synchronization algorithm,which is based on the measured distance and velocity information of underwater acoustic wireless link.We add relative velocity information in the node exchange information of synchronization protocol,which reduces the clock synchronization error by the compensation of two-way propagation time delay.At the same time,we develop an AUV prototype to vertify the clock synchronization algorithm,which can promote the robustness of synchronous data transmission between the AUV and the mother ship in the relative motion conditions.Finally,we carried out theoretical and experimental research on the serious time-varying multipath propagation with a high rate in the AUV frequency hopping modulation communication system.Our research is conducted when the sparsity characteristics of the broadband underwater acoustic communication channel are taken into consideration in the space domain,time domain,and frequency domain.The theoretical researches are conducted as follows:(1)On-Grid and Off-Grid compressive sensing technology based on DCD iterations;(2)sparse multipath DOA estimation technique based on compressive sensing with a low computing complexity;(3)channel estimation based on sparse compressed sensing with a low computing complexity;(4)passive time reversal channel shorterning technology and Minimum Mean Squared Error(MMSE)channel shortening technology based on sparse channel estimation with a single element;(5)broadband space time frequency channel modeling and space time frequency joint sparse channel estimation technology.We carry out the simulation and lake experiments.The simulation and lake experiments are shown as follows:(1)compared with the conventional OMP algorithm,the POMP-DCD and the AMP-CTLS-DCD algorithms have a higher the estimation accuracy,a lower computing complexity(the computing complexity can be reduced from O(K~2)to O(K)),a more robust numerical stability,and more easy to implement on the DSP/FPGA platform for the Off-Grid sparse parameter estimation;(2)compared with the conventional SA-OMP algorithm,space replacement SA-POMP-DCD and SA-AMP-CTLS-DCD channel estimation technology can process the Off-Grid problem with a lower computing complexity;(3)the multipath spread can be inhibited after the sparse DOA is employed after spatial filtering,and the performance(i.e.,SER and BER)of the receiver can be improved.Moreover,compared with the passive time reversal channel shorterning technology,the MMSE channel shorteming technology can overcome the phenomenon of error floor to achieve a better communication performance.