On Theories Of Anchor Deployment For Positioning Autonomous Underwater Vehicles With Sound Speed Profile

Autonomous underwater vehicles(AUVs),which are important carriers of marine information gathering and transmitting,have been widely used for a variety of underwater applications such as oceanographic surveys,object detection,and environment monitoring.When the AUV executes underwater missions,localization information is crucial for the AUV to label its collected data as well as support intelligent auto-navigation or timely remote control.Therefore,the design of underwater localization systems,which can obtain the accurate location information of the AUV,has attracted notable attention.As the core for constructing underwater acoustic localization systems,the geometry relationships between the AUV and anchors can produce significant impacts on the localization performance.However,existing works have explored the anchor deployment for AUV localization without considering the characteristics of the sound propagation in the actual underwater environment.Based on the sound speed profile(SSP),this thesis devotes to investigating the anchor-AUV geometries optimization problem for achieving highaccuracy AUV localization in the actual underwater environment.This thesis first investigates the anchor deployment problem in AUV localization based on the time-of-flight(ToF)measurement under the assumption of the constant SSP.Specifically,the relationship equation between the Fisher information matrix(FIM)and system geometry parameters based on the ToF measurement is derived under the constant SSP to formulate an optimization problem of the anchor deployment.Then,by using tools of the estimation theory,the optimization problem is converted into a minimization problem of the trace of the Cramér-rao lower bound(CRLB)matrix.In order to solve this problem,the optimization problem is transformed and simplified by adopting tools from the estimation theory and the theory of averages.Finally,an optimal anchor deployment scheme with uniform planar circumference structure is obtained,and the corresponding theoretical analysis is verified by simulation results.Furthermore,considering the fact that acoustic waves propagate along bent curves in practice underwater environments,this thesis investigates the anchor deployment configuration optimization problem in a 3-D ToF-based scenario with a widely-adopted isogradient SSP.To address this problem,the Jacobian matrix of measurement errors is rigorously derived to quantify the CRLB under the iso-gradient SSP,and then a more complicated anchor deployment optimization problem is formulated by minimizing the trace of the CRLB.For mathematical tractability,by adopting tools from the estimation theory,this problem is transformed and simplified equivalently subject to some angle and range constraints.By this,an easy-to-implement anchor-AUV geometry,referred to as the uniform sea-surface circumference(USC)deployment,is obtained.Extensive simulation results validate that the proposed USC scheme outperforms both the cube and the random deployment schemes in terms of localization performance under the same parameter settings.In addition,the obtained results also indicate that the USC's localization accuracy can stay at a satisfactory level even when the AUV moves randomly.In conclusion,this thesis provides basic support for improving the localization accuracy and performance of the AUV localization system by optimizing the anchor deployment scheme when the system is constructed under the constant or variable SSP.