Research On Distributed Long-range Underwater Acoustic Location Technology

With the accelerated pace of humans' ocean development and the implementation of china's 'maritime power strategy',with the develop of all kinds of submarines,Autonomous Underwater Vehicles(AUV),Underwater Unmanned Vehicles(UUV),self-propelled mine,and water divers,the problem of oceanic concealed positioning is needed to be solved as soon as possible.This dissertation discusses the distributed long range underwater acoustic positioning technology,which provides larger coverage area and accommodates more positioning equipments.Underwater acoustic channel has multipath characteristics and stochastic property of varieties with time,location,frequency,depth,bottom topography,surface wind and waves.Due to these facts,dramatic changes of time-varying,position-varying and frequency-varying occurred in the propagation process of sound wave,brought huge influence to signal detection,time measurement,sound velocity estimation,positioning solution and so on.In this dissertation,the implementation principle,the locating method and the error source of the distributed long-range positioning technology are analyzed theoretically and the simulation is also carried out.Time measurement and sound velocity estimation are two important factors for determining the distance between the receiver and the beacon.Due to the underwater acoustic channel on refraction and reflection,there are great differences between the actual way that acoustic signal travels and the liner distance from the transmitter to the receiver.The sound velocity at any position in the channel can't be used to calculate the distance between the transmitter and receiver directly.Aiming at this problem,this dissertation proposes a method of estimating average velocity of sound by multipath channel model of distributed positioning,solves the match problem between signal arrival time and straight-line distance.The sea experiments are carried out.Start with the distributed positioning signal form,this dissertation use spread spectrum signal with strong anti-fading ability as the long-range distributed acoustic positioning signal.The problem of low received signal to noise ratio(SNR)caused by long range transmission distance.In the distributed acoustic positioning,receiver requires the signals from multiple beacons at the same time to locate self position.According to the received signal with low signal-to-noise ratio,multipath interference and multi-access interference,this dissertation researches on the subjects of spread spectrum sequence form,sequence optimization and prioritization,usage of BOC modulation,established a distributed positioning technique of sequence prioritization.When sequence prioritizing,two constructors with sequences'Auto-correlation side peak maximum and the Cross-Correlation maximum are used to simplify the set of sequence optimization process,solve the signal optimization problem in multi-access interference.The anti-multipath and anti-multiaccess capability of spread spectrum signal is limited by the sequence correlation lower bound theory,its autocorrelation peak value and cross-correlation value can't achieve the optimal at same time.This paper established a locally optimal positioning signal group based on ZCZ sequence,improved the detectionperformance and anti-jamming ability,solved the signal arrival time accurate estimation problem in long range and low SNR condition.This dissertation carries on the experiment of the long-range distributed positioning system,the distance between each beacon is longer then 50km,and the positioning range is larger than the traditional positioning technology.The sea experiment verifies the beacon array calibration algorithm,acoustic synchronization algorithm and distributed positioning algorithm.The performance of distributed long-range positioning signal is investigated,and finally,a distributed remote positioning system based on three beacons is established.