An Improved Baseband Receiver for UHF RFID Reader Systems

Abstract

One of the key challenges in radio-frequency identification (RFID) reader system design is a sophisticated receiver technique to reliably detect the very small tag response among the interferences and noises. The passive ultra high frequency (UHF) RFID system faces a variety of problems, including interferences, signal distortion, frequency deviation, and collision in the tag backscattered signal. Recently, for improving the performance of the passive UHF RFID system, many research works focusing on the multiple access control (MAC) layer have been proposed, however, there has been little work conducted focusing on the performance of the passive UHF RFID system in practical environment from perspective of physical (PHY) layer. The PHY layer effects, such as detection errors caused by signal distortion, can significantly degrade the RFID system performance by increasing the duration of each read cycle and the number of cycles needed to read all tags.

In this thesis, in order to enhance the reliability of signal processing for passive UHF RFID systems, firstly, a baseband demodulator for RFID reader receiver is proposed to demodulate the weak tag response signal which tends to be easily distorted and has considerable frequency deviations. The proposed demodulator is very robust against strong signal distortions and large frequency deviations happening on the received backscattered signal from a passive RFID tag. Secondly, we focus on improving the tag collision resolution performance of the RFID reader receiver, and propose a collision detection (CD) scheme which enables fast and accurate CD such that achieving faster tag identification speed than conventional methods especially under noise conditions. The validity and usefulness of the proposed two methods for the RFID reader receiver is verified by both computer simulation and implementation. |RFID 리더 시스템 설계의 핵심적인 문제점은 간섭 및 잡음환경에서 아주 미약한 태그 응답신호를 정확하게 검출하는 수신기 기술이다. 수동형 UHF RFID 시스템은 역사란 된 태그 신호 중에서 간섭, 신호왜곡, 주파수 편차 및 충돌 등 많은 문제들이 존재하고 있다. 최근에 수동형 UHF RFID 시스템의 개선에 대해 MAC층에 중점을 두어 많은 연구를 수행했지만 PHY층에 시점을 둔 수동형 UHF RFID 시스템이 실제환경에서의 성능에 대한 연구가 그다지 많지 않았다. PHY층에 대한 연구 (예를 들어 신호 왜곡으로 인한 검출오류) 에서 각 인식 주기의 시간과 주기수가 모든 태그를 인식함으로써 소요한 시간이 증가되어 RFID 시스템의 성능을 급격히 저하시키는 결과를 초래하게 된다.

본 논문은 수동형 UHF RFID 시스템이 신호처리의 신뢰성을 높이기 위한 연구이다. 연구는 우선 RFID 리더 수신기에 대해 쉽게 왜곡될 수 있고 많은 주파수 편차를 생기는 미약한 태그 응답 신호를 복조 하는 베이스밴드 복조기를 제안하였다. 제안한 복조기는 수동형 RFID 태그에서 수신된 역사란 신호의 작용으로 인한 강한 신호왜곡과 대량 주파수 편차 문제를 보완할 수 있다. 다음, RFID 리더 수신기의 태그 충돌 해결에 중점을 두어 충돌 검출 방법을 제안하였다. 본 충돌 검출 방법은 잡음 환경에서 전통적인 방법보다 정확하고 빠르게 충돌 검출할 수 있어 태그 인식 속도를 제고할 수 있다. RFID 리더 수신기에 관해 제안한 두 가지 방법의 유효성과 유용성은 컴퓨터 시뮬레이션 및 구현으로 증명되었다.; One of the key challenges in radio-frequency identification (RFID) reader system design is a sophisticated receiver technique to reliably detect the very small tag response among the interferences and noises. The passive ultra high frequency (UHF) RFID system faces a variety of problems, including interferences, signal distortion, frequency deviation, and collision in the tag backscattered signal. Recently, for improving the performance of the passive UHF RFID system, many research works focusing on the multiple access control (MAC) layer have been proposed, however, there has been little work conducted focusing on the performance of the passive UHF RFID system in practical environment from perspective of physical (PHY) layer. The PHY layer effects, such as detection errors caused by signal distortion, can significantly degrade the RFID system performance by increasing the duration of each read cycle and the number of cycles needed to read all tags.

In this thesis, in order to enhance the reliability of signal processing for passive UHF RFID systems, firstly, a baseband demodulator for RFID reader receiver is proposed to demodulate the weak tag response signal which tends to be easily distorted and has considerable frequency deviations. The proposed demodulator is very robust against strong signal distortions and large frequency deviations happening on the received backscattered signal from a passive RFID tag. Secondly, we focus on improving the tag collision resolution performance of the RFID reader receiver, and propose a collision detection (CD) scheme which enables fast and accurate CD such that achieving faster tag identification speed than conventional methods especially under noise conditions. The validity and usefulness of the proposed two methods for the RFID reader receiver is verified by both computer simulation and implementation.