Tag-reader Distance Research Articles

A Multiple Baseline Approach to Face Multipath

The positioning of tagged objects by means of the phase of the backscattered RFID signal is a challenging problem. Several approaches have been conceived in the years to face the problem of the narrow bandwidth of the RFID signal, which produces a periodic, and hence ambiguous, measurement of the tag-reader distance. One possible strategy is to exploit the movement of either the tag or the reader to collect a set of phase measurements which allow to solve the aforementioned ambiguity: this is, e.g., the approach pursued by SAR (Synthetic Aperture Radar) methods. In this article we propose an alternative approach which elaborates the sequence of phase samples in order to discover additional indicators that allow to improve the effectiveness of synthetic aperture methods. In particular we develop a strategy that permits to identify, among a set of measurements, the ones more strongly affected by the multipath. If a pattern emerges among the measurements without significant multipath (and this occurs if a low to moderate level of multipath characterizes the environment), by exploiting the good subset of measurements, it is possible to achieve an improvement in the positioning estimation. The method has been developed for a straight line trajectory: numerical results are reported in this article to illustrate the approach, while experimental results confirm its effectiveness.

An algorithm for automatic grasping an UHF RFID passive tag

This paper proposes an automatic system which allows a mobile robot to reach a tagged object in an unknown environment, exploiting the Radio Frequency IDentification (RFID) technology. It is assumed that the robot has an odometry system (e.g., wheel encoders) and an RFID reader which provides it with phase-shift measurements of the RFID signal backscattered by the tagged object. Since phases are ambiguous measurements of the tag-reader distance, a Multi-Hypothesis Extended Kalman Filter is proposed to on-line extract, by fusing phase measurements with odometry readings, the range and the bearing of the unknown tag. Once the relative position of the tag is known, a control algorithm is applied to drive the robot toward the desired destination. Numerical results are reported to illustrate the approach.

Range and Bearing Estimation of an UHF-RFID Tag Using the Phase of the Backscattered Signal

The narrow bandwidth of UHF RFID signals does not allow the direct measurement of the range between the reader and the tag. A Multi-Hypothesis Extended Kalman Filter is proposed in this paper to solve this issue, by fusing the phase measurements with the odometry readings of a mobile robot. While estimating the tag-reader distance, the proposed approach provides also an on-line estimation of the bearing of the tag. The knowledge of range and bearing is beneficial in positioning-based applications as in robotics, to develop algorithms for reaching and grasping a tagged object or to localize a robot using tags as anchors, or for solving a Simultaneous Localization and Mapping (SLAM) problem if positions of both tags and robot are unknown. A few steps are usually enough to obtain a univocal effective estimate of these quantities, as long as the robot is moving over a non-straight path. A comprehensive numerical analysis supports and assesses the theory.

Effect of Distance for Chipless RFID Magnitude Coding

An implementation of the hybrid frequency-magnitude coding is presented. This technique can be applied to enhance coding capacity of already existing chipless radiofrequency identification tags without increase of complexity. The dependency of the magnitude from the tag-reader distance is discussed and a compensation technique is proposed. An increase of 2.6 bits per resonator is demonstrated from measures in office environment.

Ambient Backscatterers Using FM Broadcasting for Low Cost and Low Power Wireless Applications

Nowadays, the explosive growth of Internet-of-Things-related applications has required the design of low-cost and low-power wireless sensors. Although backscatter radio communication is a mature technology used in radio frequency (RF) identification applications, ambient backscattering is a novel approach taking advantage of ambient signals to simplify wireless system topologies to just a sensor node and a receiver (RX) circuit eliminating the need for a dedicated carrier source. This paper introduces a novel wireless tag and RX system that utilizes broadcast frequency modulated (FM) signals for backscatter communication. The proposed proof-of-concept tag comprises of an ultralow-power microcontroller (MCU) and a RF front-end for wireless communication. The MCU can accumulate data from multiple sensors through an analog-to-digital converter, while it transmits the information back to the RX through the front-end by means of backscattering. The front-end uses ON–OFF keying modulation and FM0 encoding on ambient FM station signals. The RX consists of a commercial low-cost software-defined radio which downconverts the received signal to baseband and decodes it using a suitable signal processing algorithm. A theoretical analysis of the error rate performance of the system is provided and compared to bit-error-rate measurements on a fixed transmitter-tag-RX laboratory setup with good agreement. The prototype tag was also tested in a real-time indoor laboratory deployment. Operation over a 5-m tag-reader distance was demonstrated by backscattering information at 2.5 kb/s featuring an energy per packet of $36.9~\mu \text{J}$ .

위상 잡음의 거리 상관 효과에 따른 UHF RFID 리더의 성능 분석

본 논문에서는 위상 잡음의 거리 상관 효과에 따른 직접 변환 방식의 UHF 대역 RFID 리더의 성능을 분석한다. UHF RFID 시스템은 일반적 인 무선 통신 방식과는 다르게 송신 캐 리어를 발생하는 LO 신호가 동시에 수신기의 국부 발진기로 사용되며, 이에 따라 태그 신호와 LO 신호 간의 거리 상관 효과에 의한 주기적인 신호 간섭 및 위상 잡음 감소 효과가 발생한다. 주기적인 신호 간섭 효과는 이론 및 시뮬레이션을 통해 I와 Q신호를 I/Q 다이버시티 개념으로 전력 결합함으로써 제거할 수 있음을 확인하였다. 위상 잡음 감소 효과는 전형적인 UHF 대역에서 동작하는 LO의 위상 잡음에 대한 전력 밀도 스펙트럼이 태그-리더 거리 및 옵셋 주파수에 따라 변화됨을 확인하였고, 이를 이용하여 심볼 에러 성능을 시뮬레이션 하였다. 시뮬레이션 결과, 심볼 에러에서 위상 잡음의 영향은 태그 변조 방식 중 PSK에서 특히, 변조 각도가 작을 때 크게 나타나지만, 거리 상관 효과에 의해 실제 위상 잡음이 감소되어 그 영향이 미비해짐을 확인하였다. In this paper, we analyze the performance of a direct-conversion UHF RFID reader with the range correlation effects of the phase noise. Since a UHF RFIB system uses the same oscillator to generate the transmitted carrier and the local oscillation, the periodic interference and phase noise reduction effects occur due to time delay between two signals. Through exact theory and simulation, we verify how to cancel the periodic interference phenomena using I/Q diversity combining technique. And, we analyze phase noise reduction effects due to range correlation as a function of the tag-reader distance and the offset frequency Using these results, we simulate the symbol-error-rate performance with respect to phase noise with and without range correation effects. We show that the phase noise of the local oscillator has little effect on the symbol-error-rate performance because of phase noise reduction by range correlation.