Research On The Key Technology Of RFID Positioning Based On Carrier Phase

With the rapid development of Internet of Things technology,the demand for indoor positioning is increasing in both serving the public and industrial applications,such as warehouse management,emergency rescue,smart home,etc.RFID positioning technology is widely used in indoor positioning because of its low cost,convenient deployment and good real-time performance.The existing UHF RFID positioning technology usually uses the arrival time,signal strength and other information to achieve positioning,which has the disadvantage of low positioning accuracy.In order to achieve high precision positioning of static target,this thesis studies the phase-based UHF RFID positioning algorithm,and the main research contents are as follows:(1)Aiming at the problem of large ranging error caused by the small bandwidth of traditional RFID,this paper obtains the phase information under multiple frequencies by frequency hopping,and expands the bandwidth of the system.Then the algorithm of integer ambiguity resolution of HMFCW is introduced and the influence of bandwidth,frequency hopping interval and other parameters on the algorithm performance is analyzed.Aiming at the problem that large phase error points can easily lead to errors in the integer ambiguity solution,this paper proposes the improved HMFCW algorithm on the basis of HMFCW algorithm.The improved HMFCW algorithm eliminates the phase with large error by calculating the mean value of the clustering results,and then gets the ranging value by solving the integer ambiguity.The simulation results show that the improved HMFCW algorithm can effectively solve the problem of error in the integer ambiguity solution caused by large phase error points and improve the ranging accuracy.(2)The formula of geometric dilution of precision(GDOP)is derived.The GDOP values corresponding to time difference of arrival(TDOA)algorithm and time sum of arrival(TSOA)algorithm are calculated under three typical layouts(linear,triangular,Lshaped).The results show that the GDOP value of TSOA algorithm is better than that of TDOA algorithm in three typical layouts,and the conclusion is that the location accuracy of TSOA algorithm is higher.On the basis of TSOA algorithm,the influence of horizontal distance,vertical distance and non reference point distance in transceiver layout parameters on GDOP value is explored respectively,and the optimization scheme of transceiver layout is given.(3)The RFID positioning system is built by using the software radio equipment and the R420 reader of Impinj company.The ranging effect of the improved HMFCW algorithm is verified and the positioning accuracy of the TDOA algorithm and the TSOA algorithm is compared.The experimental results show that the improved HMFCW algorithm proposed in this paper can improve the ranging accuracy to a large extent when the integer ambiguity solution results are wrong due to large phase error points.The range results of improved HMFCW algorithm are substituted into TDOA algorithm and TSOA algorithm respectively to solve the target location.The experimental results show that TSOA algorithm has higher positioning accuracy and stronger robustness.