Research On Wireless Localization Optimization Technique In Ubiquitous Environment

With the development of Internet of things and the rise of the fifth generation mobile communication system,wireless localization has become more and more important for people's life.Both the outdoor route navigation and security management under the limited space need the location information.However,the navigation services based on satellites are usually available when there is a clear sky view.Also there will be signal blocking and multipath propagation effect in space-constrained environments.Different location scenarios and systems have their own limitations and technical points.At the same time,considering the localization accuracy,equipment cost and the algorithm complexity,it is necessary to explore the wireless localization optimization technology in ubiquitous environment.Through the review of the related literature and analysis of the current algorithms,three major research directions are studied in this paper:the joint algorithm of time and localization in Wireless Sensor Networks(WSN),the localization and tracking methods in Low Earth Orbit(LEO)dual-satellites geolocation system and the localization technology in Non-Line-of-Sight(NLOS)environment.The research and innovation points are as follows:Synchronization and localization are two of the main components in WSNs.Considering the asynchronous anchors,this paper derived an estimator for determining the anchor nodes clock offsets,clock skews and source localization.The anchor nodes are separated into a number of groups to reduce the unknown parameters.Within each group,the received signals at the anchor nodes are sampled synchronously with respect to a common local clock.Use the time difference of arrival(TDOA)to eliminate the asynchronous problem between the source node and anchor nodes.The Regularization theory is introduced to modify the Taylor series to ensure the iteration convergence.The clock parameters of anchor nodes and the source localization are obtained utilizing the modified Taylor series method.LEO satellites have the characteristics of low orbit,large number and low delay.In the geolocation system of LEO TDOA and frequency difference of arrival(FDOA),the satellites ephemeris error,the satellites clock error and measurement error will be considered.For the static radiation source with unknown location,obtain the anchor nodes clock offsets,clock skews and source localization applying the iterated algorithm.For tracking the mobile radiation source,correct the measured value in real time according to the pseudo range difference algorithm.Firstly,calculate the correction parameters of TDOA and FDOA measurements by the known reference station.Then the correction parameters are taken to modify the TDOA and FDOA measurements of the mobile radiation source in real time.At last,track the motion trace based on extended Kalman filter.The simulation results show that the joint algorithm and the difference correction algorithm can both locate and track target effectively.An improved angle of arrival algorithm and cooperative localization are presented to solve the signal shield and lack of reference stations.Cooperative localization employs mobile devices(MDs)not only communicate with reference devices but also the MD.This idea can reduce the cost of reference node layout.Select the cooperative node according to whether there is a line-of sight path to the unknown MD.The located mobile devices utilizes the joint angle-of-arrival(AOA)estimations of the line-of-sight path measured by both known MD and unknown MD to construct areas of possible mobile devices.The least-square solution will give the result.Simulations show that the performance of the new AOA scheme surpasses the existing localization schemes.