Research On Rf Self-interference Signal Suppression Technology In UHF RFID Reader

The radio frequency identification(RFID)technology based on light scattering realizes the non-contact automatic identification of the target by means of wireless.Among them,passive ultra-high frequency(UHF RFID)systems are used in intelligent information systems such as cargo handling,urban traffic management,school education,and industrial management,and have become the mainstream of RFID technology in the development of Internet of Things technology.In UHF RFID,when the transmitted signal from the transmitter reaches the receiver through a circulator or a directional coupler,the receiver will generate self-interference signals due to insufficient isolation and return loss of the antenna.The key to improving the performance of UHF RFID systems is to suppress self-interfering signals.By controlling the strength of the self-interference signal generated on the link of the UHF RFID reader,the sensitivity of the receiver of the reader is improved.This thesis further studies the suppression of RF self-interference signal of UHF RFID reader.According to the self-interference phenomenon of the leakage signal of the radio frequency side in the UHF RFID system,a self-interference signal elimination method based on FPGA-based radio frequency combined baseband is designed,and its suppression capability is theoretically analyzed and simulated.The main content and work of this thesis are as follows:First: briefly summarizes the basic technical principle of UHF RFID system,introduces the performance of UHF RFID system in detail,and analyzes and expounds the formation principle of self-interference signal in UHF RFID front-end circuit communication and the suppression process of radio frequency self-interference signal.Finally,the influence of self-interfering signal in the receiving process is analyzed.Second: The thesis designs the adaptive carrier cancellation algorithm and demodulation algorithm for self-interfering signals.Mainly is the comparative analysis of the LMS algorithm and the RLS algorithm to the self-interference signal suppression.The thesis also studies and implements a demodulator based on CORDIC algorithm.It can not only demodulate the amplitude and phase information of I and Q signals,but also generate sine wave signals in numerically controlled oscillators.The algorithm is implemented on MATLAB.Third: The thesis adopts a method of UHF RFID reader radio frequency and baseband to jointly suppress self-interference signals.According to the correlation between self-interference signals and reference signals,an adaptive filter based on Euclidean distance is proposed and designed.Optimize the LMS suppression algorithm.The algorithm is implemented inside the FPGA,which improves the suppression effect by 20 d B compared with the traditional LMS algorithm.And a numerical control passive vector modulator is designed at the RF end of the UHF RFID system,which has the advantage of not introducing additional noise.The radio frequency joint baseband cancellation method can combine the suppression technologies of the baseband end and the radio frequency end to suppress self-interference signals more effectively.This thesis builds an FPGA module and a hardware platform.Through simulation tests and experiments,the suppression ratio of 36.65 d B is measured against self-interference signals.Compared with the traditional cancellation method,the suppression ratio is improved by about 5d B.The interference signal method can effectively solve the self-interference signal problem of the UHF RFID system.