Key Technology Research And System Implementation Of Underwater Multi-node Communication And Relative Positioning

This paper studies the underwater multi-node communication and relative positioning technology,and designs a more suitable for underwater nodes(such as AUV,snorkeling beacon,etc.)cluster formation work positioning integration of communication equipment,the main contributions include: the system uses OFDM technology for communication,adopts a single-vector hydrophone to realize active positioning,and realizes underwater information exchange,mutual positioning and command transmission.Firstly,the characteristics of underwater acoustic channel are studied.The underwater acoustic channel is established according to the distribution of sound ray in the measured test data,and the time-invariant sparsity of channel is verified in shallow sea environment.This paper focuses on the channel estimation technology in underwater acoustic OFDM communication system.Targeting at channel of clustered sparse feature,an orthogonal matching pursuit(OMP)algorithm based on Chirp Z-transform can be used to estimate channel of path delays.The simulation results show that the improved algorithm improves the estimation accuracy and adopts the fast calculation method with low complexity,which reduces about 30% of the system’s calculation,which is suitable for system implementation.Secondly,this paper uses the single-vector hydrophone to complete the azimuth estimation,combined with the response time delay ranging method to achieve the system positioning function.In this paper,the azimuth estimation algorithms of narrowband signals in time domain and frequency domain are studied.The azimuth estimation algorithms of wideband signal such as histogram and weighted histogram are studied.The simulation results show that the frequency-domain average sound intensity method has higher estimation performance and more stable estimation performance for narrowband signals.The histogram method can estimate wideband continuous spectrum targets and has better anti-line spectrum interference effects,while the weighted histogram method is suitable for line estimation.spectrum target and has better performance against wideband coherent interference.According to the needs of the system,this paper implements the direction finding algorithm of frequency domain sound intensifier on the processor.Then,according to the technical indicators,this paper designs the signal frame structure and parameters of the system,and calculates the sound source level of the transmitter and the dynamic range of the receiver’s preamplifier.According to the parameter requirements,the hardware platform design and driver programming are completed based on STM32F767 digital processing platform,including A/D acquisition circuit and signal conditioning(preamplification,power amplification)circuit.At the same time,the paper compiled the software flow of the master and slaved in the formation operation,including timing design,signal processing flow,communication protocol and processor instructions to maintain the normal operation of the system.This paper focuses on the implementation of synchronous detection,OMP channel estimation algorithm based on Chirp-Z transform and single-vector hydrophone positioning algorithm on this platform,and uses fast algorithms for optimization to ensure the real-time and accuracy of the system.Finally,the main functional circuit of the system is tested and the electrical connection adjustment in the laboratory is carried out.Testing the the communication rate of the system to verify the feasibility of the system function.Furthermore,through the sea trials,the function of system’s communication and positioning of direction finding,ranging are verified,which indicicates that the system meets the requirements of technical indicators,and it can be applied to underwater multi-node scenarios such as AUV cluster formation and frogman collaborative operation.