Research And Implementation Of Indoor Positioning System Based On Bluetooth 5.1

With the development of Internet of Things technology and intelligent terminal,indoor positioning technology has become a key research topic at home and abroad.In January 2019,Bluetooth Technology Alliance announced a new direction finding and positioning technology,compared with positioning technology based on Bluetooth received signal strength,the positioning accuracy of Bluetooth can be upgraded to sub-meter level.Bluetooth direction finding technology has many advantages,such as low power consumption,medium cost,high accuracy,strong portability,etc.,and has become a research hotspot in the field of indoor positioning.Based on the above background,this thesis designs and studies the Bluetooth positioning system by using the direction finding method of the angle of arrival in the Bluetooth direction finding technology.The research contents are as follows:Firstly,the main features and functions of each layer of Bluetooth Low Energy protocol stack are introduced.This thesis analyzes the process of transmitting and receiving the direction finding signal of Bluetooth with CTE,and analyzes and tests the RF characteristics of Bluetooth,such as the wireless channel frequency,frequency deviation,carrier frequency deviation.The propagation model of wireless signal is deduced and established.The filtering effect of RSSI filtering algorithm and the angle estimation effect of phase interferometry and multiple signal classification are discussed.Secondly,the systematic error of uniform linear array in direction finding and the error source of phase measurement are analyzed.The optimization algorithm is proposed on the basis of angle estimation by using phase interferometry method.In the section of antenna phase difference calculation,a phase difference optimization algorithm based on gradient descent is proposed to reduce the interference of abnormal data during antenna sampling.Aiming at the problem that the accuracy of angle estimation becomes worse when the incident angle is larger,the angle correction algorithm based on C4.5 decision tree is further proposed by taking advantage of the correlation between the physical channel and the phase difference fluctuation when Bluetooth sends data packets.Experimental results show that,compared with the existing algorithms,the accuracy of angle of arrival is improved effectively.Then,aiming at the problem of large noise in the original measurement information,an extended Kalman filter algorithm is derived based on the principle of trilateral positioning and triangulation,using historical information for tracking and filtering,and simulation verification is carried out.By analyzing the problem of imbalanced positioning accuracy faced by the current positioning system,a fusion positioning algorithm of AOA and RSSI is proposed,which overcomes the problem of low accuracy when only using RSSI for distance measurement and the defect of partial blind areas in triangular positioning.Finally,an indoor positioning system based on Bluetooth 5.1 was built,and an upper computer was developed to support position coordinate display,trajectory rendering,switching of different modes and data export,etc.The test environment and test scheme of the positioning system were designed,and the average Angle accuracy of-60°～60° was calculated to be 4°,and the average positioning accuracy of Bluetooth in the measured area was 0.26 m,which realized the sub-meter level position accuracy.