The Three-dimensional Positioning Method Based On Optimization Principle In Thenon-line-of-sight Environment

With the development of Internet and improvement of wireless communication technology,mobile phone(hand-held terminal)has become a necessity of life.As a result,the location based service(LBS)has gradually become a business with good prospects and huge potential market.Traditional GPS positioning technology works well in normal circumstances,but it do not perform well in some special situations,such as underground garages and inside buildings.Use wireless mobile communication base stations to determine the position of hand-held terminal can avoid the problems of traditional positioning methods.Therefore,this localization technology becomes the focus of attention.Traditional localization methods generally use the time-of-arrival measured by of base stations to determine the position of hand-held terminals.However,in the real circumstances,the measurement of time-of-arrival often affected by many factors such as clock asynchronization caused by instrument error,non-line-of-sight propagation effect,signal-to-noise ratio and etc.Those factors will cause different deviation of the measurement of time-of-arrival.First of all,the research situation of wireless positioning technology is introduced.The basic algorithm and characteristics of the commonly wireless positioning methods is also discussed.The difficulties of using these methods in real circumstances to determine the position of hand-held terminal are pointed out.Secondly,in order to obtain the precise positioning of the hand-held terminal in any scene,the influence of the non-line-of-sight propagation effect on the time of arrival is first considered.Non-line-of-sight propagation is the most influential factor,so the least squares algorithm based on time difference of arrival and non-line-of-sight propagation influence factor is designed.The nonlinear equations are transformed to linear equations.The least square algorithm is used to get the analytical solutions.Applied to the actual scene,the results of algorithm show that the X and Y axis error of the hand-held terminal coordinates is very small,the accuracy of model is good enough.However,due to the position of the base stations and different coordinates' orders of magnitude,there is a significant error at the Z axis,and the fluctuation range is very large.Thirdly,the error effects caused by other factors such as clock insynchronization are taken into account.The coordinates calculated by the least squares algorithm with non-line-of-sight propagation influence factor are set as the initial position of the hand-held terminal.Section model used on the coordinate as the initial position of hand-held terminals.The minimum sum of squared error between the measuring distance and the actual distance is taken as the objective function.Based on the initial position and the objective function,the non-linear programming model with constraint is established.Steepest descent method is used to solve it.The results show that the method can locate the hand-held terminal coordinates more precisely,and the error on each dimension is smaller.