Research And Realization Of Error Suppression Method On RFID Ranging Technology Based On Carrier Phase

With the rapid development of economic society and information technology,people's demand for Location Based Service(LBS)is increasing,which gradually makes indoor localization technology becoming a focus of research.The current mainstream indoor localization technologies are based on WIFI,Bluetooth,Radio Frequency Identification(RFID)and so on.Among them,RFID-based indoor localization technology has attracted the attention of many companies and researchers due to its low cost and wide application.As a key part of RFID indoor localization technology,the accuracy of RFID ranging technique directly affects the localization accuracy.Therefore,the research on indoor ranging technology is of great significance.Based on this background and the analysis of the composition and working principle of the RFID system,this thesis deeply studies the key technologies of ranging,including the channel estimation and phase extraction technology,phase error analysis and suppression technology,multipath suppression technology and phase cycle ambiguity resolving technology,etc.Furthermore,a test platform based on Software Defined Radio(SDR)is established to test and verify the ranging technology by this thesis.The main research contents of this thesis are as follows:First of all,this thesis analyzes the advantages and disadvantages of ranging technology based on Receive Signal Strength Indicator(RSSI),time information and carrier phase.This thesis also studies the extraction process and error model of carrier phase,and analyzes sources of the phase error in the system and its impact on the accuracy of ranging in detail.In addition,in order to solve impacts of the phase inversion and other phase abnormal problems of carrier phases extracted by proposed ranging system,this thesis presents corresponding processing techniques to improve the accuracy of the phase.Then,this thesis studies the Ultra-high Frequency(UHF)RFID indoor ranging technology based on multipath suppression to address the influence of multipath on the accuracy of indoor ranging.In order to solve the problem of low distance resolution caused by insufficient bandwidth of traditional RFID communication signals,a frequency hopping extended bandwidth technology is proposed.Frequency hopping is used to achieve bandwidth expansion and obtain multi-frequency Channel Frequency Response(CFR)data.Afterwards,the methods based on the Inverse Fast Fourier Transform(IFFT)and Inverse Non-uniform Discrete Fourier Transform(INDFT)are presented to identify the Line-of-Sight(LOS)signal and obtain the rough distance estimation.A multipath suppression algorithm,which takes rough distance estimation of the LOS signal as a filtering factor,is proposed to suppress the phase of the multipath signal and enhance the phase of the LOS signal.Then the phase cycle ambiguity is solved with the phase after multipath suppression by utilizing the Chinese remainder theorem and clustering algorithm,so as to obtain the Time of Flight(TOF)of the LOS signal for ranging.Finally,a data test platform is set up based on Universal Software Radio Peripheral(USRP)of Ettus Company and R420 reader of Impinj Company to verify the proposed algorithm.Experimental results show that the proposed ranging technology with the phase error suppression can achieve centimeter-level accuracy,which can meet the demand of indoor high-precision ranging.