Distributed Positioning Methods Of Mobile Nodes In Underwater Acoustic Sensor Networks

Since underwater acoustic sensor network(UASN)has been widely used in marine resources exploration,data collection,disaster warning,underwater navigation,military operations and other scenarios,it has been the hotspot of marine research informatization.As a fundamental technology of UASN,positioning is used to estimate the location of underwater targets,track underwater nodes,and optimize the performance of the medium access control and routing protocols.Therefore,designing effective underwater positioning techniques in UASN is significant meaningful.Considering the characteristics of UASN,we study the distributed passive underwater positioning in this paper.Firstly we propose a positioning algorithm based on time difference of arrival(TDoA)in which the positioning messages are propagated synchronously under consideration of long positioning period and the asynchronous clock between the underwater node and beacons.Then we carry out the implementation and analyze the error of the positioning algorithm in detail.However the TDoA positioning algorithm has two main shortcomings:the assumption of constant sound speed,which will result in positioning error;and the high cost for synchronization of all beacons.We propose a multipath-aided ranging positioning algorithm and we consider the sound speed profile(SSP).The positioning algorithm combines the TDoA positioning algorithm and multipath-based ranging algorithm,where the surface-reflected paths of positioning signals from seabed-beacons help to realize ranging,so that we can accurately position with measured SSP.Considering the high cost for synchronization of all beacons in TDoA positioning,we propose a seabed-beacons-aided positioning alsorithm.in which the clock of surface-beacons is only supposed to be synchronized.The problem of clock asynchronization can be solved by the means that the seabed-beacons transpond the positioing signals from surface-beacons.Theoretical analysis and simulation results show that the proposed positioning algorithms can solve the problems of TDoA positioning algorithm efficiently.The positioning algorithms based only on positioning messages can solve the localization problem but are not suitable for tracking tasks,because it cannot accomplish tasks in a real-time and energy-efficient manner at the same time.Hence,we propose a filtering-based positioning and tracking method.Firstly,we construct a positioning system that can maximize the coverage area,and then design the broadcasting time sequence of each beacon's positioning signal.Considering the problem of clock asynchronization,the time differences between the arrivals of different positioning signals in the same packet group or consecutive groups are used as observations and how to process a different number of positioning signals in each group is considered in the method.Given the position-dependency characteristics of the effective sound speed,the effective sound speed is modeled as an updating state variable in order to decrease positioning error.Theoretical analysis and simulation results show that the proposed positioning and tracking method can apply to the asynchronous passive positioning and tracking of underwater mobile node.We carry out a lake trial for the TDoA positioning algorithm in which the positioning messages are propagated synchronously and the filtering-based positioning and tracking method.We verify the feasibility of the TDoA positioning algorithm,and then verify the influence of buoys' topology size and mobile node's location on position performance.In addition,the feasibility of the filtering-based positioning and tracking method is verified.