Research On Inverted Ultra-short Baseline Positioning Technology

Underwater positioning is a key technology to support the exploration and development of marine resources,and acoustic positioning is one of the most commonly used underwater positioning methods.The inverted ultra-short baseline(i USBL)is an underwater acoustic positioning system,in which,by deploying the receiving array,the underwater mobile nodes can obtain their positions by receiving positioning signals sent by the beacon.Due to the special structural design,the i USBL can integrate communication signals and positioning signals,and improve the positioning accuracy of underwater nodes by using the direction information of the beacons provided by the receiving array.Direction estimation is a key problem in i USBL positioning technology.In order to solve the problems of small number of array elements and small spacing,this dissertation proposes a two-stage direction estimation method,which includes the angle of arrival estimation of signals and the direction estimation of acoustic source.Firstly,angles of arrival of different baselines are estimated.Considering the difference of signal to noise ratio(SNR)at different frequency points of the actural receiving wideband signals,a SNR-weighted subspace method of incoherent signal is proposed,which reduces the DOA estimation error.Then,the direction of acoustic source is estimated by linear regression method using the DOA estimation results in the first stage,and an improved method is proposed for low SNR environment to improve the estimation robustness.Simulation results show that the proposed method has better performance of direction estimation than the traditional method.To reduce the direction estimation error caused by system errors,the dissertation studies calibration methods for i USBL,and uses nonlinear least squares to calibrate the errors caused by the array position errors and the array installation deflection angles.In the calibration of array installation deflection angles,to address the issue of inaccurate beacon position,an iterative calibration method of beacon position and installation deflection angles is proposed,which can calibrate the beacon position and the deflection angles at the same time.To address the issue of curved acoustic lines,an installation deflection angles calibration method that is independent of the acoustic velocity gradient is proposed.Based on the integrated design of communication and positioning signals for i USBL,this dissertation establishes the positioning model of underwater node base on i USBL,and gives the corresponding positioning method.Then,under the condition of asynchronous time between the beacon and the node,a passive positioning method of the underwater mobile node based on i USBL is proposed.Because of the direction information provided by i USBL,this method reduces the positioning error of the underwater mobile nodes.Then,the i USBL/dead reckoning combined positioning method of underwater mobile node based on kalman filter is presented,which further reduces the positioning error.Last,the dissertation built the USBL receiving array experimental platform,and carried out the sea test and data analysis,but the positioning accuracy of the system needs improvement.Then,the dissertation built the beacon experimental platform using laboratory’s independently developed underwater acoustic communication device.This dissertation studies the positioning technology of inverted ultra-short baseline.The research work and results can provide reference for the realization and application of i USBL system.