Byung-Jun Jang

Effects of Reader-to-Reader Interference on the UHF RFID Interrogation Range

In this paper, the effects of ultrahigh-frequency band passive radio-frequency identification (RFID) reader-to-reader interference are investigated in terms of the interrogation range. A reader-to-reader interference model based on interference statistics is proposed, and the nominal interrogation range of a desired reader is derived by this model. In order to evaluate the RFID reader-to-reader interference quantitatively, the interrogation-range-reduction ratio (IRRR) is also defined. For a simple case with only one interfering reader, the analytic and experimental results are in good agreement. Reader-reader distance achieving 0% IRRR, indicating no interference between the readers, is 1200 m for the multiple-reader environment. Additionally, IRRR values are calculated in various environments according to the North American and Korean regulations. The maximum number of allowable interfering readers is then calculated by the proposed interference model and a target IRRR.

Interference Analysis of UHF RFID Systems

In this paper, RFID reader-to-reader interference is analyzed from the point of view of interrogation range. To evaluate RFID interference quantitatively, the new figure-of-merit, interrogation range reduction ratio (IRRR), is defined. In order to show the usefulness of IRRR, its value is calculated in various environments. Additionally, the calculated IRRR values are verified by measurements using two RFID readers and an RFID tag. IRRR can be referred to an important design parameter to analyze more complex interfering problems in instances of actual RFID system deployment.

Effects of reader interference on the RFID interrogation range

In this paper, the effects of radio frequency identification (RFID) reader interference are investigated in terms of the interrogation range. In order to evaluate RFID interference quantitatively, the signal-to-interference ratio (SIR) equation is initially derived, and the interrogation-reduction range ratio (IRRR) defined. IRRR is a function of the distance between a desired reader and an interfering reader. Co-channel interference (CCI) and adjacent-channel interference (ACI) instances of IRRR are simulated. Simulation results show that reader-reader distances achieving 0 % IRRR, indicating no interference between the two readers, are 1200 m and 35 m for the CCI and ACI cases, respectively. The IRRR factor is inversely proportional to the reader-reader distance in both cases. The simulation results were also verified by measurement results using an ETRI UHF RFID system. Measurement results were found to be in good agreement with the simulation results. It can be concluded that the present simulation results are reliable and applicable in analyses of more complex interfering problems in actual RFID system deployment instances.

A Passive Circulator with High Isolation using a Directional Coupler for RFID

In radio-frequency identification (RFID) system, a directional coupler has been used to isolate RX from TX due to its simplicity and low cost compared with a circulator. Nevertheless, a conventional microstrip directional coupler has inherent drawback of poor isolation due to unequal phase velocity between even and odd mode. In this paper, a newly proposed circulator using a microstrip directional coupler is proposed to achieve good isolation between TX and RX. The proposed circulator is used for UHF band RFID reader with a single antenna, of which the operating frequency band is 860 MHz-960 MHz. The measurement of the fabricated circulator using a modified directional coupler exhibits excellent isolation of 64 dB and directivity of 49 dB in its frequency band. The validity of the proposed circulator is demonstrated by comparing the TX leakage at the RX port of RFID reader system with that of a conventional directional coupler

Reverse-Link Interrogation Range of a UHF MIMO-RFID System in Nakagami-

In this paper, the reverse-link interrogation range (RIR) of ultrahigh-frequency-band passive radio-frequency identification (RFID) is analyzed for single-input and single-output (SISO) and multiple-input and multiple-output (MIMO) systems with maximal-ratio combining in the pinhole channel, where each channel is modeled as an arbitrarily correlated Nakagami-m distribution. Under the assumptions of perfect channel estimation and no interference, the closed-form expression of average RIR is derived, involving various parameters, such as the number of antennas, correlation, reader structure, and Nakagami- m shaping factor. The results show that the employment of multiple antennas at a reader causes the received SNR to change favorably and contributes to the improvement of the average RIR. Particularly, for the bistatic structure and Rayleigh fading (m = 0 dB), a 3 × 3 MIMO-RFID system can achieve 60% gain in the average RIR compared to the SISO-RFID system. In order to consider more realistic environments, finally, we investigated the influence of interference and imperfect channel estimation on the average RIR of the MIMO-RFID system in the uncorrelated Rayleigh fading channel.

m

High-frequency (HF) band wireless power transfer systems ofier the promise of cutting the last cord, allowing users to seamlessly recharge mobile devices as easily as wireless communication. Yet there are still many technical issues that need to be overcome. Among them, one of the most di-cult problems is maintaining impedance match over a short range, where the distance between a transmitter and receiver could vary. In this paper, the efiect of impedance mismatch of a HF- band wireless power transfer system is carefully investigated and two compensation methods are suggested to overcome this within a short range, where frequent impedance mismatch can occur. Each method has pros and cons. In order to verify the feasibility of the proposed methods, HF-band wireless power transfer systems, with a pair of rectangular loop resonators, were designed. The e-ciency and input impedance variation were simulated and measured. From these results, proposed methods show enhanced e-ciency performance than a typical wireless power transfer system without any compensation circuits.

Fading Channels

This paper presents a voltage-controlled PIN diode attenuator and its temperature-compensation circuit composed of a thermistor and simple operational amplifier circuits. After carefully investigating the temperature characteristics of PIN diode attenuators, we designed voltage-controlled PIN diode attenuators showing the linear attenuation characteristics of 16 dB with input voltage within the operating temperature range. The fabricated attenuator has demonstrated the improvement of attenuation variation from 15 to 0.5 dB in the temperature range from -15 to 65/spl deg/C.

HF-BAND WIRELESS POWER TRANSFER SYSTEM: CONCEPT, ISSUES, AND DESIGN

This paper presents a non-contact measurement method of vital signal by the use of multiple-input multiple-output (MIMO) bio-radar system, configured with two antennas that are separated by a certain distance. The direction of arrival (DOA) estimation algorithm for coherent sources was applied to detect vital signals coming from different spatial angles. The proposed MIMO bio-radar system was composed of two identical transceivers sharing single VCO with a PLL. In order to verify the performance of the system, the DOA estimation experiment was completed with respect to the human target at angles varying between 50° and 50° where the bio-radar system was placed at distances (corresponding to 50 cm and 95 cm) in front of a human target. The proposed MIMO bio-radar system can successfully find the direction of a human target.

Voltage-controlled PIN diode attenuator with a temperature-compensation circuit

In this paper, a newly invented circulator for T/R switch of UHF radio-frequency identification (RFID) application is proposed to overcome TX-to-RX leakage problem. A microstrip coupled-line directional coupler is used for this passive circulator and the isolation characteristic is drastically improved not by complex method such as compensating phase velocity, but by considering both directional coupler itself and imperfect input impedance of the employed antenna. The measurement result of the proposed circulator using modified microstrip coupled-line directional coupler with employed antenna shows excellent TX-to-RX leakage suppression in the 860 MHz - 960 MHz, more than 45 dB enhancement at the center frequency compared to the conventional coupler. Experimental verification using RFID system is also performed to prove the validity of the proposed circulator

Detection of Human Vital Signs and Estimation of Direction of Arrival Using Multiple Doppler Radars

In this paper, we propose a simple design method of a wireless power transfer system using 13.56MHz loop antennas. This method can simple design a wireless power transfer system by only using the measurements of coupling coefficients and the equations for equivalent circuit model about loop antennas without the complicated electromagnetic analysis. Using the proposed design method, a wireless power transfer system with a pair of loop antennas operating at the frequency of 13.56MHz, which have a dimension of 50×50 cm2, is designed and implemented. The input return loss, coupling coefficient, efficiency, and input impedance variation with respect to the distance between loop antennas were measured. The proposed design method provides good agreements between measured and predicted results. Also, the wireless power transfer system with impedance matching circuits designed by the proposed design method shows two times higher efficiency characteristics than the case with the general 50 Ω impedance matching circuits. Therefore, we verified that our design method could be an effective tool to design a wireless power transfer system.