| The Underwater Acoustic Sensor Network(UWASN)plays a significant role in the exploration and development of the ocean.In UWASN,precise positioning guarantees underwater nodes to complete various tasks by accomplish path planning,obstacle avoidance,and safe return.Traditional long baseline(LBL)positioning systems have high costs of deployment and retrieval,while short baseline(SBL)and ultra-short baseline(USBL)positioning systems suffer limited accuracy in the abysmal sea.Therefore,designing an underwater acoustic positioning system that ensure positioning accuracy and reduces costs is of interest to researchers.A single beacon-based positioning method has been proposed in the industry,which uses the slant distance of one beacon node and the motion information of the underwater mobile nodes to fulfill positioning tasks.At present,most underwater positioning models are based on synchronous UWASN framework.However,clock synchronization between nodes is difficult to achieve because of the complex underwater environment.In addition,most existing positioning mechanisms require the underwater mobile nodes to send an inquiry or response signal,which increases the energy cost of the node and tends to expose the nodes.Based on the above system requirements,it is of great importance for both research and industry communities to design a single beacon based underwater mobile node positioning method.Given that the measurement of slant distance is affected by bending acoustic ray because of the change of the sound speed,we layer the sound speed profile by assuming equal gradient in each layer.First,we study the trajectory equation and path parameters of acoustic ray propagation within a single layer,which is then extended to multiple layers The slant distance and propagation delay are derived by using the acoustic trajectory,and the average sound speed's calculation method is given.Considering the requirement that the underwater mobile nodes do not send information and the characteristic that the nodes are difficult to synchronize,we propose a passive positioning model for asynchronous underwater mobile nodes.The positional relationship between adjacent states is constructed by dead reckoning information from underwater mobile nodes,and we can,along with the distance equation,estimate the position of mobile nodes.Moreover,we establish a buffered state model of underwater mobile nodes,and utilize a position estimation method based on total least squares(TLS),which transforms the equation solution based mathematical problem into the information processing based estimation problem,thereby improving the positioning accuracy.The simulations show that in a sea area of 3000 m×2000 m,the position estimation error of the underwater mobile node is mainly less than 100 m,and the error goes down to be within 20 m in the area close to the beacon node.Considering the requirement of tracking the position of underwater mobile nodes,we propose a sequential tracking method.For the underwater mobile node clock's drift and the inaccurate measurement of the dead reckon information,we construct the state and measurement equations by extending the state.The measurement equation is linearized using Taylor's expansion,and the extended Kalman filter(EKF)is used to realize the position tracking of the underwater mobile node.The simulation results show that the position tracking error is less than 90 m in the sea area of 3000 m×2000 m.We carried out a lake trial in Qiandao Lake to verify the proposed position estimation and tracking method.The experimental results show that the position estimation error of the underwater mobile node is less than 40 m,and the tracking error is mainly within 30 m.In conclusion,the positioning method proposed by the paper can realize the positioning of the underwater mobile node. |
