Research On High Precision Indoor Location And Clock Synchronization Algorithms Based On UWB

With the continuous advancement of science and technology,high-precision location services are receiving more and more attention.The Global Navigation Satellite System(GNSS)can provide more accurate location services outdoors,but it cannot be accurately positioned indoors.Wifi positioning technology can achieve a wide range of positioning in the outdoor,but indoor positioning accuracy can only reach about 2 meters;Bluetooth positioning technology can achieve a small range of positioning,the same accuracy is not high,generally 3-15 meters;Geomagnetic positioning technology,although the positioning accuracy is slightly improved,up to 0.1 meters to 2 meters,but before the positioning,it is necessary to use the mobile client to record the magnetic field in different directions of the target location.The process is cumbersome.The Ultra Wide Band(UWB)technology is different from other wireless communication technologies.It has the advantages of good concealment,strong anti-multipath and narrow-band interference,and high transmission rate,which can make full use of spectrum resources.On the other hand,time-based high-precision indoor positioning requires premise of high-precision clock synchronization.However,irregular changes such as crystal drift and aging make it impossible to describe with accurate models and accurately predict time.It is very difficult to synchronize the clock,so it is necessary to study synchronization.The main research results of this paper are as follows:First of all,aiming at the problem of inaccurate timestamp calculation and inconsistent message processing delay among nodes in wireless clock synchronization,which leads to large clock deviation and low synchronization accuracy among synchronization nodes,an SDS(Symmetrical Double-sided,SDS)clock synchronization algorithm based on UWB technology is proposed.By optimizing and upgrading the existing frame structure,a clock counting value is added to the message frame sequence.Accurate timestamps are formed by exchanging poll,response,final messages between two nodes and fixing the same message processing delay at each node requiring synchronization,so as to form a precise timestamp.The clock counting value from the main node is used to make a difference with the local clock value,and the clock difference is used to adjust the local voltage temperature control complementary crystal oscillator so that it can approach the clock of the main node step by step and achieve clock synchronization.The experimental results show that the synchronization accuracy of this method is 1.2 ns.Secondly,due to the influence of antenna delay error,latitude and longitude,humidity and other factors,system errors lead to inaccurate positioning.A linear fitting optimization UWB positioning algorithm is proposed to pre-process the distance before the formal positioning.The results show that the proposed linear fitting optimization algorithm reduces the ranging error by 39%.Finally,aiming at the problems of large deviation of some data in the positioning results caused by non-line-of-sight,multi-path and so on,as well as blurred positioning by single positioning algorithm,etc..CTK-UWB(Chan-Taylor-Kalman,CTK)localization algorithm is proposed.The basic idea is to use Chan algorithm to get the initial coordinate of the tag to be located,and use the initial coordinate as the starting iteration point of Taylor algorithm to locate accurately,that is,C-T joint positioning.By satisfying the iteration threshold,the accurate positioning results can be output.The coarse data can be eliminated by improved Kalman filter.The results show that the improved Kalman filter can effectively eliminate the outliers.After C-T joint positioning,90%of the positioning results under dynamic line-of-sight are within the range of 0.085m in one-dimensional error.