RFID Read Range Estimation System

ABSTRACT

This study is on RFID read range estimation system. Operating range is one of the most significant criteria in evaluating the performance of  RFID systems, especially UHF RFID systems. That  is  because  a  longer operating  range can create more potential application opportunities and ensure a more reliable performance. The operating range is determined by the whole RFID  system design rather  than  just  a part of it.  Hence,  it is worth doing some analysis to find out the methods for evaluating   the  operating range and  which factors,  in an overall system design,  may play a key role   in improving the operating range.

CHAPTER ONE

1.0                                          INTRODUCTION

1.1                            BACKGROUND OF THE STUDY

Most tag machinery manufacturers, such as Muehlbauer and Bielomatik [1], provide fundamental online mechanism that tries to read tag IDs in the near field, and hence validates tag’s usability. For UHF RFID applications, tag usability is a very rough indicator and cannot characterize the performance of a tag accurately. In practice, effective reading distance is the key performance index of a tag because most online proofed tags are inadequate for implementation due to the insufficient reading distance.

For tag manufactures, to characterize the effective reading distance of an UHF RFID passive tag, the simplest approach is to gradually position the sampled RFID tag away from interrogator’s antenna in a large space until 50% or less of signal is received. However, such approach implies low productivity because it is a time consuming process. Moreover, in an opening area, environmental electromagnetic interference may significantly influence the measurement accuracy on effective reading distance [2-4].

To eliminate the environmental electromagnetic interference, the present state-of-the-art approach is to measure the effective reading distance inside a large anechoic chamber [5-7]. However, the use of large anechoic chamber implies high capital investments. In addition, such approach is still a time consuming process.

Since current approaches to characterize the effective reading distance of UHF RFID passive tags are costly and time consuming, an economic approach to accelerate the characterization process is needed. To propose such an innovative approach, this study reviews the traditional approach and the fundamental background of electromagnetic wave propagation in advance. Afterward, the theoretical equations for this innovative approach are derived. Finally, an experimental study is conducted to demonstrate the feasibility of this innovative approach.

1.2                                                  PROBLEM STATEMENT

When the read range of an antenna is not known it will affect the signal strength of the antenna. Most current re- search considers the powering region of a reader to be determined only by its read range (i.e., distance). However, read-accuracy also depends on the relative orientations of reader and tag antennas and their polarizations. In particular, when tag positions are not fixed, the locations of reader antennas relative to the tags can have a significant effect on the success of the interrogation processes. This paper uses Friis’ Equation to explicitly consider orientations and polarizations while addressing the problem of determining the best locations for a set of reader antennas at a scanning portal. The objective is to maximize the size of the powering region in order to maximize read-accuracy. A methodology for deter- mining the powering region with multiple antennas is developed along with an enumeration approach to determine optimal antenna locations.

1.3                                                   AIM OF THE PROJECT

The main aim of this work is to discuss signal descriptions and formulations for the radio frequency (RF) front-end of a passive backscatter radio frequency identification (RFID) reader working at ultra high frequencies (UHF). At the end of this work a set of design considerations aiming to improve the read range are outlined.

1.4                                              PURPOSE OF THE PROJECT

The main purpose of this work is to evaluating the performance of RFID systems, especially UHF RFID systems.

1.5                                  SCOPE OF THE PROJECT

We describe a methods of locating an RFID tag. One method transmits tag location signals at a plurality of different frequencies from a plurality of different antennas spaced apart by more than a near field limit distance. The processing determines a phase difference at the plurality of different frequencies by determining a phase difference between either i) two or more of the transmit signals resulting in a maxima in the returned signal RSSI or ii) a first transmit signal and its corresponding return signal. The range determining uses return signals weighted by signal strength. Further data which may be used for averaging may be generated by using the above techniques along with changes in the polarisation state of the transmit and receive antennas and/or physical reconfiguration of the antennas (e.g. switch the transmit and receive elements).

Currently, for manufacturing UHF RFID passive tags, the online inspection mechanism is very simple. This mechanism tries to read tag IDs in the near field, and hence validates tag’s usability. For UHF RFID applications, tag usability is a very rough indicator and cannot characterize the performance of a tag accurately. In practice, effective reading distance is the key performance index of a tag.