Keio University, Graduate School of Media and Governance
MAUI Project
Ph.D. Dissertation

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ACADEMIC YEAR 2007 (March 23rd, 2008)
TITLE High performance UHF-band RFID inventory

Reliability and reading speed are important research topics in UHF-band RFID inventory, which represents a process of cataloging RF tags in the reading area. This research comprised of the following two subthemes; the reliability and the acceleration of RFID inventory respectively.

In ``Subtheme 1: Permissible Link Quality for RFID Anti-Collision in a Practical Environment," the permissible link quality in a practical radio environment was quantified, and its result could be applied to RFID site designs. Since UHF RFID shares the frequency band with other RFID and/or other wireless systems, it is important to determine how much interference can be applied without causing a significant degradation of anti-collision speed. This strongly relates to the required separation distance between contending wireless systems. In this theme, the permissible link quality for RFID anti-collision in a practical environment was discussed by considering an erroneous communication link, taking into account of bit encoding and the type of interference. This research used the quantification of permissible link quality experimentally along with protocol simulations and the mathematical analyses. An international standard protocol, employing frame slotted ALOHA, was used as the air protocol. For these investigations, a protocol simulator was developed. The validity of the simulation was confirmed with analytical values based on Poisson distribution and an experiment. The investigation in the return (tag to reader) link, and the forward (reader to tag) link, were analyzed separately. As result of the protocol simulation, it was revealed that it is generally important to secure the Pulse Error Rate 10-4 or better in both return and forward links for the anti-collision of 64 or less tags without causing excessive anti-collision speed degradation. The quality of the return link may be relaxed when the application does not require a fast anti-collision. The degradation of the forward link, on the other hand, may entail loss of important commands, resulting in extremely slow anti-collision. It was measured experimentally that the required link quality could be relaxed by up to 10dB in the return links and by 5dB in the forward link when the primary source of interference originates in the interfering readers.

In ``Subtheme 2: Acceleration of UHF-band RFID Inventory Leveraging Capture Effect," the acceleration of the RFID inventory with the dynamic frame ALOHA was achieved leveraging the capture effect even without a priori knowledge of the radio propagation model. Capture effect represents the effect in which one of the radio packet can be successfully received when plural packets collides in a time slot because of the electric power difference. In the existing studies, the radio propagation model needs to be established before leveraging the capture effect. In this research, the capture occurrence was estimated directly using the observable numbers, i.e., the number of empty slots, success slots, and collision slots in an ALOHA frame. Moreover, the RFID inventory was accelerated by optimizing the frame length using the estimated capture occurrence. The fundamental performance of the proposed algorithm was verified using protocol simulations. The capture occurrence can be estimated accurately by the proposed technique and the effect of acceleration was significant when the capture occurrence was high. Moreover, it was clarified that the estimation method for the backlog number of RF tags considering the capture effect greatly contributes to the acceleration. The acceleration effect and stability of the proposed method was evaluated also with a commercial RFID reader. It was experimentally confirmed that the propose method excels existing dynamic framed ALOHA method by approximately 20%. The advantage is significant in the practical radio environment where there is large electrical power distribution on replies from RF tags.

Keywords: 1. RFID, 2. Anti-collision, 3. Permissible link quality, 4. RFID site design, 5. Capture Effect, 6. Acceleration, 7 Certainty

CONTACT To obtain the whole paper, please contact;
KAWAKITA, Yuusuke ( kwkt at )

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