Biography
Enrollment Date: 2009
Graduation Date：2015
Degree：Ph.D.
Defense Date：2015.06.06
Advisors：Zhihua Wang Chun Zhang
Department：Institute of Microelectronics，Tsinghua University
Title of Dissertation/Thesis：Research on Key Issues of Localization System based on UHF RFID Technology
Abstract:
UHF RFID localization has attracted wide attention and been researched due to its system characteristics. With the expansion of its applications, the requirements for system power consumption, precision and hardware cost are becoming increasingly higher. In this dissertation, the system structure of the UHF RFID localization is designed and validated on the basis of research on the reader, the tag, and the communication between them, and research has been made on key issues of the location system, including power consumption, efficiency and carrier leakage. A TDOA based UHF RFID localization system, in which the time difference is estimated by the correlation of pseudorandom sequences. A command used for localization is added over the ISO 18000-6C protocol, and the ranging code is designed to achieve high precision of the system. This system can locate multiple tags at the same time utilizing the good orthogonality of the ranging code. A transmitter with high efficiency is proposed to achieve high output power with low power consumption. On this basis, a system-on-chip reader system, consisting of an RF transceiver, a digital baseband, MCU, and a host interface is designed and implemented in 0.18 μm CMOS process. The power consumption of the reader is 500 mW. The power amplifier emits about 21 dBm output power and has power-added efficiency of 43%, reducing the power consumption of the reader effectively. A tag emulator which supports the command for localization is proposed. Based on the analysis of the responses of multiple tags to the reader, Gold code is chosen as the ranging code for its good performance of the auto-correlation and cross-correlation. And a multi-tag emulator is proposed to emulate the responses of multiple tags，which is capable of emulating the responses of 50 ISO 18000-6C passive tags at a 40 MHz clock speed with a link data rate of 40 kbps. An adaptive carrier leakage cancellation system for UHF RFID reader with one antenna is implemented. The isolation between the transmitter and receiver is improved by tuning the load impedance of the direct coupler. And conjugate Gradient Descent algorithm with variable step is used to improve the convergent speed and algorithm stability. This system makes the isolation from TX to RX achieve about 70 dB. To test and verify the performance of the proposed UHF RFID localization system, a reader test platform with single transmitter and multiple receivers based on Virtual Instrument is designed and implemented. By cross-correlation of the signals at two receivers directly while locating single tag, and cross-correlation between the signals received with the pre-stored sequences while locating multiple tags, the influence of the frequency offset of the ranging code on the performance of time difference estimation is eliminated. Measurement result shows that the ranging precision of the proposed UHF RFID localization system is about 10 cm.