Active RFID Tag Positioning System

With the continuous development of the Internet of Things technology and the continuous improvement of integrated circuit technology,Radio Frequency Identification(RFID)tags have gradually reduced costs and improved cost performance,making large-scale applications possible.RFID's features make it possible to track and manage the goods and share the acquired information in time,which will reduce the communication cost and improve the operation efficiency of the system.In many fields,RFID tags are gradually replacing barcodes and two-dimensional codes as key signs for item identification,and are used to obtain important information about items.If the RFID tag can be used to locate the object while obtaining this information,which can expand its application in more field.The small size,low cost,good confidentiality,and non-contact reading and writing characteristics of RFID tags make it not only applicable to item positioning and management,but also to personnel positioning and tracking.This thesis mainly studies the positioning system of active RFID tags.We have studied the current research status of RFID positioning technology at home and abroad and typical RFID positioning methods,and aiming at the characteristics of inflexible operation of the current radio direction finding system and the relatively expensive whole set of hardware equipment.The software defined radio(SDR)combined with the angle of arrival(AOA)method is used to construct the entire positioning system.Compared with previous research work,the SDR can flexibly implement various test algorithms,obtain higher accuracy test values of the AOA,and improve positioning accuracy.And the SDR is suitable for different application environment,can be quickly deployed,easy to transplant.Under the premise of not significantly affecting the overall positioning accuracy,the system has the characteristics of low cost,rapid deployment,and high portability,which improves the timeliness of the system.The research contents and innovations of This thesis are as follows:a)This thesis tracks the research status of RFID technology at home and abroad,and makes in-depth research on the concept,research status and application fields of this discipline.The commonly used positioning methods such as time of arrival,time difference of arrival,AOA and received signal strength are analyzed and compared,and common algorithms for AOA such as MVDR method and multi-signal classification method are studied and introduced.And combined with its own needs using MUSIC algorithm combined with SDR equipment to build a positioning system.b)According to the characteristics of SDR equipment and active RFID tags,the positioning system is designed and built on the basis of fully considering the factors that affect the positioning accuracy of the system,such as the different local vibration of the SDR,the asynchronous sampling clock and the SNR of the received signal at the receiver.The whole positioning system is divided into two parts: transmitting and receiving.The transmitting part mainly designs the signal type,signal frequency and signal transmission flow chart.In the receiving part,a linear uniform antenna array is designed according to the characteristics of MUSIC algorithm,and the corresponding algorithm module is constructed.According to the hardware characteristics of SDR,an external clock source device for USRP is designed,and a sampling point compensation module and a phase compensation module are constructed.According to the requirements of the positioning system,the compass module is built to display the AOA in real time.Combined with the relevant knowledge of digital signal processing,the above modules are connected with the basic modules such as filtering module and digital type conversion,and the signal processing flow chart is constructed.The transmitting part and receiving part are combined to build the whole positioning system.c)The system was tested indoors and outdoors under the UHF frequency band,and the influence of different signal strengths,different signal frequencies,and metal obstacles and non-metal obstacles on positioning errors were compared and analyzed.The test results show that the positioning system has the characteristics of low cost,rapid deployment and high portability without significantly affecting the overall positioning accuracy,can be used for the positioning of active RFID tags.