UHF RFID System Research Articles

Analysis of UWB Tag Backscattering and Its Impact on the Detection Coverage

The joint adoption of RFID and UWB technologies is a promising solution to overcome most of the limitations of current RFID systems. In particular, UWB RFID based on the modulation of the backscatter signal represents a good option when tags cost, size and power consumption are stringent requirements. In this context, while for current UHF RFID systems an extensive literature is present, only few studies have concentrated on the backscattering of UWB signals. In the present work, we deal with the electromagnetic analysis of the UWB RFID tag backscattering, which is adopted to characterize the interaction of the tag with a close object. We investigate tag backscattering first from an analytical perspective, then through simulations and measurements. Measured data is then post-processed, and performance in terms of detection coverage analysis is finally assessed to evaluate the effects of an object in proximity to the antenna.

Design of anti-collision integrated security mechanism based on chaotic sequence in UHF RFID system

Collision and security issues are considered as barriers to RFID applications. In this paper, a parallelizable anti-collision based on chaotic sequence combined dynamic frame slotted aloha to build a high-effciency RFID system is proposed. In the tags parallelizable identification, we design a Discrete Markov process to analyze the success identification rate. Then a mutual authentication security protocol merging chaotic anti-collision is presented. The theoretical analysis and simulation results show that the proposed identifcation scheme has less than 45.1 % of the identifcation time slots compared with the OVSF-system when the length of the chaos sequence is 31. The success identification rate of the proposed chaotic anti-collision can achieve 63% when the number of the tag is 100. We test the energy consumption of the presented authentication protocol, which can simultaneously solve the anti-collision and security of the UHF RFID system.

Numeric Evaluation on the System Efficiency of the EPC Gen-2 UHF RFID Tag Collision Resolution Protocol in Error Prone Air Interface

Efficient resolution of the tag collisions is the key for the RFID systems to be universally adopted. To resolve the tag collision occurred in the UHF RFID system, the EPC Gen-2 protocol, proposed by the EPCglobal Inc., was adopted as an international standard and have been widely accepted in industry. However, little research works has been taken to evaluate the performance of this protocol in nonperfect and error prone air interface. In this paper, to evaluate the performance of the EPC Gen-2 protocol, a system efficiency model is proposed, and, based on the model, numeric simulations are performed to evaluate the EPC Gen-2 protocol in error prone air interface. Simulation results reveal that the system efficiency of the EPC Gen-2 protocol is seriously affected by the capture and noise effects.

UHF RFID 태그의 최대 인식 거리를 얻기 위한 태그 칩의 임피던스 산출 방법

수동형 UHF RFID 시스템에서 태그의 최대 인식 거리는 태그 칩과 안테나 사이의 임피던스 정합과 리더의 프로토콜 파라미터 설정에 따라 직접적인 영향을 받는다. 하지만 칩 임피던스 산출 방법과 프로토콜 파라미터가 최대 인식 거리에 미치는 영향에 대한 연구는 전무한 실정이다. 따라서 본 논문에서는 기존 방법(데이터 시트와 전용 RFID 테스터를 이용)과 제안된 방법(상용 리더를 이용)으로 칩의 임피던스를 산출한 후 이 값으로 태그를 제작해 인식 거리를 비교함으로써, 인식 거리를 극대화하는 칩 임피던스 산출 방법에 대한 비교분석을 하였다. 제안된 방법으로 산출된 임피던스에 공액 정합된 태그가 상용리더를 이용한 인식 거리 측정 실험에서 기존 방법과 비교하여 최대 73 % 인식 거리의 개선을 보였다. In a passive UHF RFID system, the impedance matching between tag antenna and chip as well as the protocol parameter settings in a reader plays important role in determination of the maximum read-range. Almost no paper, however, has dealt with the above issues in relation with the maximum read range. In this paper, two known methods (of using the value from data sheets and proprietary RFID tester) and our proposing method in chip impedance evaluation are compared in terms of maximum read range. The read range of tags whose antenna impedance is conjugate matched with the chip impedance obtained from the proposed method is improved maximum 73 % more than that of tags from the other methods.

Planar circularly polarized tag antenna with compact operation for UHF RFID application

A novel compact design of planar circularly polarized (CP) tag antenna for UHF RFID system is proposed. By introducing the Y-shaped slit as the feed structure, the measured half-power bandwidth of the proposed CP tag antenna can be more than 135 MHz (860–1000 MHz), which includes the entire operating bandwidth for worldwide UHF RFID system. The obtained 3 dB axial-ratio (AR) bandwidth can be about 10 MHz suitable for Taiwan UHF RFID applications. The proposed tag antenna reduces the antenna size by at least 30% since the antenna size is only 40 × 40 × π mm2. The simulated peak gain and antenna efficiency are approximately 0.4 dBic and 91% for Taiwan UHF RFID band. Meanwhile, with omnidirectional reading pattern, the measured reading distance is about 7.2 m. Good tag sensitivity was obtained across the desired frequency band.

밀집리더환경에서 RFID 리더를 위한 채널 할당

RFID 시스템에서 리더간 간섭은 일정한 서비스 영역에서 제한된 주파수를 사용하기 때문에 발생하며 수동형 태그의 가독율을 떨어뜨리는 주요 원인이 된다. 그러므로 제한된 주파수 자원 환경에서 가독율을 최대화하려면 리더간 주파수 간섭을 최소화시켜야 한다. 본 논문에서는 RFID 리더간 주파수 간섭 최소화 문제를 FDM/TDM 혼합방식의 제약만족문제로 모델링하고 기존의 백트래킹 탐색 알고리즘을 적용하여 각각의 리더에게 최적의 채널을 할당한다. 제약 만족 문제의 해를 구하기 위해서 백트래킹을 이용한 깊이우선탐색을 실행하는데 이 때 탐색되는 노드의 순서를 효과적으로 배열하는 변수 순서화 방법이 중요하다. 본 논문의 실험에서 적용된 변수 순서화 알고리즘들은 그래프 채색에 효과적인 것으로 알려져 있다. 제안한 제약만족문제 모델의 성능을 입증하기 위하여 수동형 UHF RFID 시스템 환경에서 시뮬레이션하여 간섭조건을 만족하면서 각각의 리더에게 최적의 채널을 할당한다. Reader-to-reader interference in RFID system is occurred due to the use of limited number of frequencies, and this is the main cause of read rate reduction in the passive RFID tags. Therefore, in order to maximize the read rate under the circumstances of limited frequency resources, it is necessary to minimize the frequency interference among RFID readers. This paper presents a hybrid FDM/TDM constraint satisfaction problem models for frequency interference minimization problems of the RFID readers, and assigns optimal channels to each readers using conventional backtracking search algorithms. A depth first search based on backtracking are accomplished to find solutions of constraint satisfaction problems. At this moment, a variable ordering algorithm is very important to find a solution quickly. Variable ordering algorithms applied in the experiment are known as efficient in the graph coloring. To justify the performance of the proposed constraint satisfaction problem model, optimal channels for each readers in the passive UHF RFID system are allocated by using computer simulation satisfying various interference constraints.

Development of Optically Transparent Ultrathin Microwave Absorber for Suppression of Misidentification Possibility of UHF-RFID System

Recently, wireless telecommunication devices have been used with the worldwide spread of the mobile phone, wireless local area networks WLAN, and UHF-radio frequency identification UHF-RFID. Therefore, EMI problems have also been serious. In the case of indoor use, the wireless telecommunication environment is degraded by multiple reflection interference. That interference must be controlled in order to improve wireless communication conditions. In particular, improvement of the multipath environment is regarded as indispensable for assuring reliability UHF-RFID systems. In this paper, an ultrathin microwave absorber is described as a technology for improving the multipath environment for UHF-RFID system. Additionally, provision is made for transparency of this absorber, because microwave absorbers should not increase the blind area of the observation camera in the region in which the UHF-RFID system is used around the entrance gate of offices or warehouses. Verification of tag identification probability improvement with this absorber in an actual warehouse is also presented.

Planar Broadband Circularly Polarized Antenna With Square Slot for UHF RFID Reader

Novel circular polarization (CP) design of planar broadband antenna with square slot for UHF RFID system is proposed and experimentally studied. By insetting the arc-shaped strip into the square slot, the proposed CP design can easily be achieved with the impedance bandwidth ( RL ≥ 10 dB) of about 142 MHz (15.3% @ 931 MHz) and the 3 dB axial-ratio (AR) bandwidth of about 166 MHz (17.7 % @ 940 MHz) for UHF RFID applications. The measured peak gain and radiation efficiency are about 6.8 dBic and 98% across the operating band, respectively, with nearly bidirectional pattern in the XZ- and YZ-plane.

A Passive UHF-RFID System for the Localization of an Indoor Autonomous Vehicle

A global localization system combining odometry data with radio frequency identification (RFID) readings is proposed. RFID tags are placed at the ceiling of the environment and can be detected by a mobile robot unit traveling below them. The detection of the tags is the only information used in the proposed approach (no distance or bearing to the tag is considered available), but differently from similar localization setups reported in the literature, only a small number (about one each square meter or less) of tags are used. This is possible using a suitable tag's antenna in ultrahigh frequency band, expressly designed to obtain regular and stable RFID detection regions, which allows us to consider an efficient Kalman filtering approach to fuse RFID readings with the vehicle odometry data. A satisfactory performance is achieved, with an average position error of about 0.1 m. The hardware/software localization setup described in this paper is cheap and easy to use and may provide a satisfactory approach in several industrial and domestic scenarios.

Development of Optically Transparent Ultrathin Microwave Absorber for Ultrahigh-Frequency RF Identification System

The application of UHF radio-frequency identification (RFID) systems is rapidly increasing. However, the reliability of indoor telecommunication is adversely affected by multiple reflection interference. Consequently, to establish a highly reliable UHF-RFID system, it is essential to improve the multipath environment. This paper describes an ultrathin microwave absorber that is designed to improve the multipath environment of UHF-RFID systems. This absorber is optically transparent so that it does not create blind areas for surveillance cameras installed near an UHF-RFID system (e.g., at the entrance of an office or a warehouse). The improved tag identification probability using this absorber is demonstrated in an actual warehouse.

RCSMA: Receiver-Based Carrier Sense Multiple Access in UHF RFID Systems

RFID tag identification is a crucial problem in UHF RFID systems. Traditional tag identification algorithms can be classified into two categories, ALOHA-based and tree-based. Both of them are inefficient due to the incidental high coordination cost. In this paper, we bring CSMA into UHF RFID systems to enhance tag read rate by reducing coordination cost. However, it is not straightforward due to the simple hardware design of passive RFID tags, which is unable to sense the transmissions or collisions of other tags. To tackle this challenge, we propose receiver-based CSMA (RCSMA) in this paper. In RCSMA, the reader notifies the tags channel condition. According to different sensing results of reader's notifications, the tags take corresponding actions, e.g., random back off. RCSMA does not require special RFID tag hardware design. An absorbing Markov chain model is presented to analyze the performance of RCSMA and shown to be consistent with the simulation results. Compared with optimized ALOHA-based algorithms and optimized tree-based algorithms, RCSMA can enhance the tag read rate by 30-70 percent under different reader and tag data rates.

DDC: A Novel Scheme to Directly Decode the Collisions in UHF RFID Systems

RFID has been gaining popularity due to its variety of applications, such as inventory control and localization. One important issue in RFID system is tag identification. In RFID systems, the tag randomly selects a slot to send a Random Number (RN) packet to contend for identification. Collision happens when multiple tags select the same slot, which makes the RN packet undecodable and thus reduces the channel utilization. In this paper, we redesign the RN pattern to make the collided RNs decodable. By leveraging the collision slots, the system performance can be dramatically enhanced. This novel scheme is called DDC, which is able to directly decode the collisions without exact knowledge of collided RNs. In the DDC scheme, we modify the RN generator in RFID tag and add a collision decoding scheme for RFID reader. We implement DDC in GNU Radio and USRP2 based testbed to verify its feasibility. Both theoretical analysis and testbed experiment show that DDC achieves 40 percent tag read rate gain compared with traditional RFID protocol.

Risk Management: Integration of a passive UHF-RFID system in medical environment

Article Risk Management: Integration of a passive UHF-RFID system in medical environment was published on August 31, 2012 in the journal Biomedical Engineering / Biomedizinische Technik (volume 57, issue SI-1-Track-J).

Multi-tag spatial multiplexing in UHF RFID systems

Multi-tag spatial multiplexing in UHF RFID systems

UHF RECTENNA USING A BOWTIE ANTENNA

In this paper, a rectifying antenna (rectenna) for energy scavenging applications is presented. The proposed device uses a modifled bowtie antenna to collect the electromagnetic energy coming from UHF RFID systems, and RF Schottky diodes to convert it into DC power. Experimental results at 866MHz demonstrating an RF-to- DC conversion e-ciency of about 65% with an input power density of 60W/cm 2 will be presented and discussed.

A Multifrequency Passive Sensing Tag With On-Chip Temperature Sensor and Off-Chip Sensor Interface Using EPC HF and UHF RFID Technology

State-of-the-art passive RFID tags are limited in terms of functionality and operating range due to the limited power that can be converted from the electromagnetic field. This is why state-of-the-art wireless sensor systems are mostly battery-based if a high operating range is required. The proposed ultralow-power on-chip sensor unit and off-chip sensor interface which provides enough energy to supply various sensors with a power consumption up to the milliwatt range make it possible to remotely power the proposed RFID tag and use it as wireless sensor node. Equipping sensor nodes with RFID functionality not only enables identification and logistic applications but also an easy integration of the sensing tag into existing RFID systems. Exploiting the different characteristics of HF and UHF RFID systems, namely the large operating range in UHF and the high available power in HF, increases the flexibility and applicability of wireless sensor nodes. This paper presents a remotely powered multifrequency sensing tag according to the EPC HF and EPC Class 1 Gen 2 UHF standard developed in a 0.13- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu$</tex></formula> m low-cost CMOS process. Input powers of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}$</tex></formula> 10.3 or <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}$</tex></formula> 7.9 dBm at a frequency of 900 MHz are necessary to operate the sensing tag with activated on-chip sensor unit or off-chip sensor interface, respectively.

Compact Metallic RFID Tag Antennas With a Loop-Fed Method

Several compact, low profile and metal-attachable RFID tag antennas with a loop-fed method are proposed for UHF RFID systems. The structure of the proposed antennas comprise of two parts: (1) The radiator part consists of two shorted patches, which can be treated as two quarter-wave patch antennas or a cavity. (2) A small loop printed on the paper serves as the feeding structure. The small loop provides the needed inductance for the tag and is connected to the RFID chip. The input impedance of the antenna can be easily adjusted by changing loop dimensions. The antenna has the compact size of 80 mm × 25 mm × 3.5 mm, and the realized gain about dB. The measured results show that these antennas have good performance when attached onto metallic surfaces.

Energy-Efficient Wireless Sensing Using a Generic ADC Sensor Interface Within a Passive Multi-Standard RFID Transponder

A successive approximation analog-to-digital converter (ADC) is presented, whose components make use of effective ultralow-power techniques to enable wireless sensing with passive and semi-passive sensor nodes. Compared with prior publications, new layout enhancements were applied to the capacitive array of the integrated digital-to-analog converter (DAC) to achieve less distortion caused by mismatch. In addition, it is shown that the digital circuit parts consume most of the available energy. Therefore, digital near-threshold operation is proposed to minimize their consumption. The applicability of the ADC is demonstrated in a UHF RFID system. Within this system, it is applied as a core of a sensor interface integrated into a passive multistandard RFID transponder. The EPC protocol used for communication ensures the compatibility with standard UHF RFID readers while the sensor data is acquired using custom commands. Single sensor readings are demonstrated as well as continuous sensor data transmission without further interaction of the reader device. A stable transponder reading distance of 6.5 m is achieved. The integrated ADC consumes only 525 nA at 40 kSps and 0.9-V supply voltage. Under these conditions, an ENOB of 7.23 is achieved and thus a FOM of 79 fJ/conversion-step.

ACSP: A novel security protocol against counting attack for UHF RFID systems

Current research on UHF RFID system security mainly focus on protecting communication safety and information privacy between a pair of specific tags and its corresponding interrogation reader. However, instead of stealing detailed private information of tags, adversaries may just want to estimate the cardinality of tags, which is named counting attack. Unfortunately, most existing protocols are vulnerable to counting attack. To defend against this attack, in this paper we propose ACSP, a novel Anti-Counting Security Protocol. ACSP employs session identifier and provides a corresponding authentication metric to verify the commands sent by the reader. To handle counting attack, ACSP periodically updates the session identifier, and securely identifies tags with encryption. We evaluate the performance of ACSP through theoretical analysis and qualitative comparison. Results show that ACSP can efficiently withstand counting attack as well as defending against regular security threats as existing protocols.

UHF RFID Reader Implementation for EPC C1G2 Protocol

UHF RFID system has been mainly used in logistics,production and supply chain management. The implementation of UHF RFID reader with excellent performance is still challenging. This paper presents a UHF RFID reader implementation for EPC C1G2 protocol. EPC C1G2 physical layer architecture and some critical modules like encoder ,decoder, modulator and demodulator are described in details. All modules are verified in FPGA and the experiments demonstrate that the designed RFID reader baseband system could perform well.