Research On Key Technologies Of UWB Asynchronous Positioning For Intelligent Vehicles

The key technologies of intelligent vehicles mainly include environment perception,decision planning,and coordinated control.Among them,high-precision positioning is one of the key issues of environment perception,which is crucial to the development of intelligent vehicles.Intelligent vehicle positioning technology can be divided into absolute positioning of single-vehicle and relative positioning between vehicles.Although satellite positioning is the most commercialized and widely used positioning technology,it is only suitable for the absolute positioning of outdoor open areas.It has limitations when applied to indoor,indoor-outdoor transition areas,as well as relative positioning.For these limitations,this paper studies the key issues involved in the vehicular applications of the Ultra-wide Band(UWB)positioning technology.A new asynchronous UWB positioning system configuration and its time measurement error correction and base-station layout optimization method are proposed for absolute positioning.The HC-ASI positioning algorithm suitable for any base station layout is further proposed.The indoor-outdoor transition area positioning is based on the UWB positioning system,Real-time Kinematic(RTK)satellite positioning technology,and Dead Reckoning(DR).For seamless indoor and outdoor positioning facing the relative positioning,the HOMO-LM positioning algorithm combined with the triangle constraint is proposed to address the precision dispersion during long-distance positioning,applied to the vehicle’s anti-collision warning.The specific work is as follows:Firstly,the defects of the classical UWB positioning system configuration are analyzed.A new asynchronous time-difference positioning system is constructed,which has the advantages of low delay,no capacity limitation,convenient network expansion,easy arrangement,and low installation cost.For this system configuration,a time measurement error self-correction method of the three UWB modules interaction communication is proposed,significantly improving measurement accuracy.Then,the UWB base-station layout optimization method considering environmental constraints is proposed,with minimizing the root mean square error of multi-sampling points’ horizontal dilution of precision in the experimental area as the optimization target,the environmental limitations as the constraints.The multi-base station layout is optimized by the genetic algorithm,and experiment is conducted.The test results show that the positioning accuracy in the experimental area is greatly improved by adjusting the installation layout of the base stations.Secondly,for the classic Chan method,the positioning problem is of poor robustness or even unsolvable in the bases where the stations are close to the plane layout.For this issue,the HC-ASI(Hyperboloid Coplanar and Asymptotic Surface Intersection)algorithm is proposed,where the intersection point of the hyperboloids’ common surfaces and the progressive surfaces is used to determine the target position.According to the degree of expansion of the hyperboloids,two conditions are discussed.One is determining a common plane by two hyperboloids and the other is replacing a hyperboloid with its progressive surfaces.The nonlinear hyperboloid equation set is converted into a linear plane equation set for calculation.In cases where progressive faces are used,the optimal solution is approximated by Taylor Series.The HC-ASI algorithm inherits the advantages of the Chan method,which can linearize the twosurface equations and use redundant information for least square estimation.This method can also be applied to any base station layout,avoiding the unsolvable problem of Chan method under the a specific base station layout.The experimental results show that the positioning accuracy of the HC-ASI algorithm is much higher than that of the Chan method under the special base station arrangement conditions,and in general conditions,the HC-ASI algorithm is not weaker than the accuracy of the Chan algorithm.Then,the advantages and limitations of different positioning technologies in the indoors and outdoors are analyzed.In order to provide the vehicle with smooth positioning information from outdoor to indoor,a seamless positioning scheme based on RTK/UWB/DR is proposed.In the indoor and outdoor transition areas,the weighted function of positioning fusion and the boundary condition of positioning switching are constructed by the horizontal dilution of precision of RTK and UWB systems.On this basis,an RTK/UWB/DR fusion estimation model based on extended Kalman filtering is established to supplement the positioning of interrupt areas and further improves the smoothness of the transition.The test results show that the designed seamless positioning system can provide seamless positioning indoors and outdoors under the experimental scenario.Finally,a UWB-based vehicle relative positioning system is established.Three UWB modules are installed on the top of each vehicle in a triangular configuration,and the distance between any two modules on the two vehicles respectively can be ranged.The HOMO-LM localization algorithm that can effectively suppress the accuracy dispersion problem during long-distance localization is proposed for this system.The target position is calculated as the initial value by the improved spherical intersection projection method.The triangle side length and directed area are used as constraints to optimize the target position.Then the relative position and orientation of the two vehicles are obtained by least-square coordinate transformation.Furthermore,DR is combined with the vehicle relative kinematic model to further improve the relative positioning accuracy and explore the feasibility to implement vehicle collision warnings based on the UWB/DR fusion system.Simulation and experimental results show that the HOMO-LM positioning algorithm proposed in this paper can significantly improve the relative positioning accuracy.The constructed UWB relative positioning system can achieve better accuracy than a commercial millimeter-wave radar.It is also feasible to perform vehicle collision warnings based on this system.