• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.9A
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• pp.814-821
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• 2005

When there are many tags using the same frequency around the reader in RFID system, they disturb each other and in the end their response cannot be received by the reader. To solve this disturbance and fast identify the tags, the anti-collision algorithm, which is the core technology in RFID system, is needed. We propose two ALOHA-type Dynamic Framed Slotted ALOHA(DFS-ALOHA) algorithms using Dynamic Slot Allocation(DSA), which dynamically allocates the frame size in accordance with the number of tags and Tag Estimation Method(TEM), which estimates the number of tags around the reader. We also compare the performance of the proposed DFS-ALOHA algorithms with that of the conventional Framed Slotted ALOHA (FS-ALOHA) algorithms and the algorithms proposed by Vogt using OPNET simulation. According to the analysis, the two proposed DFS-ALOHA algorithms(DFS-ALOHA I and DFS-ALOHA II) show better performance than the conventional ALOHA-based algorithms regardless of the number of tags. Although the two proposed DFS-ALOHA algorithms show the similar performance, BFS-ALOHA ll is better because it is easier to be implemented in the system and the complexity is lower.

• The Journal of the Acoustical Society of Korea
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• v.33 no.2
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• pp.126-132
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• 2014

In this paper, a DFSA (Dynamic Framed Slotted ALOHA) based anti-collision algorithm is described and a performance improved algorithm of DFSA and FSA is proposed. The proposed method makes use of expected values and has merits in operation speed by estimating closest value of the number of tags on a single operation. The algorithm compares and analyses number of empty slots and collide slots in accordance with the number of tags, which enables estimation of actual number of tags. we simulated the proposed algorithm and compared it with conventional methods. Results show that our method needs average 18.8 rounds to identify all tags. In case of less than 1000 tags, an average of 18.2 rounds is necessary and an average of 19.2 rounds is needed to identify all tags for more than 1000 tags. The proposed algorithm improves processing speed by 3.1 % comparing to DFSA with cancellation strategy, 10.1 % comparing to DFSA, 37.5 % comparing to FSA(Framed Slotted ALOHA).

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.9
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• pp.29-37
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• 2004

In RFID system one of the problems that we must solve is to devise a good anti-collision algorithm to improve the efficiency of tag identification which is usually low because of tag collision. Among the existing RFID anti-collision algorithms, Framed Slotted ALOHA algorithm though simple, has a disadvantage that the number of slots used to identify the tags increases exponentially as the number of tags does. In the paper, we propose a new anti-collision algorithm called Partial-Response Framed Slotted ALOHA(PRFSA) which restricts the number of responding tags by dividing the tags into a number of groups when there are large number of tags and changes the frame size when there are small tags. Since the proposed algorithm keeps the frame size and the number of responding tags in such a way that can increase slot utilization, the algorithm shows superior performance to the existing ones. The simulation results showed that the proposed algorithm improves the slot efficiency by 85～100% compared to the existing algorithm.

• The KIPS Transactions:PartC
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• v.16C no.2
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• pp.267-274
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• 2009

For the implementation of a RFID system, an anti-collision algorithm is required to identify multiple tags within the range of a RFID Reader. There are two methods of anti-collision algorithms for the identification of multiple tags, conclusive algorithms based on tree and stochastic algorithms based on slotted ALOHA. In this paper, we propose a Dynamic Framed Slotted ALOHA-Slot Congestion(DFSA-SC) Algorithm. The proposed algorithm improves the efficiency of collision resolution. The performance of the proposed DFSA-SC algorithm is showed by simulation. The identification time of the proposed algorithm is shorter than that of the existing DFSA algorithm. Furthermore, when the bit duplication of the tagID is higher, the proposed algorithm is more efficient than Query Tree algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.7B
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• pp.686-693
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• 2009

In this paper, we propose an efficient tag sleep method utilizing empty time slots for improving the tag collection performance in active RFID systems. In the proposed tag sleep method, the reader detects the occurrence of empty time slots by carrier sensing and utilizes the wasted empty time slots to transmit sleep commands to the collected tags throughout the framed slotted aloha-based tag collection process, resulting in reducing the time required for tag collection. Via the simulation experiments, we evaluated the performance of the tag collection applied with the proposed tag sleep method, compared with that of the basic tag collection. The simulation results showed that the tag collection applied with the proposed tag sleep method could reduce the average tag collection time by 12.28%, 12.30%, and 13.31 %, for the framed slotted aloha with the fixed 128 time slots and 256 time slots, and the dynamic framed slotted aloha anticollision protocols, respectively.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.5
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• pp.70-77
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• 2009

In an RFID network consisting of a single reader and many tags, a framed and slotted ALOHA, which provides a number of slots for the tags to respond, was introduced for arbitrating a collision among tags' responses. In a framed and slotted ALOHA, the number of slots in each frame should be optimized to attain the maximal efficiency in tag cognizance. While such an optimization necessitates the knowledge about the number of tags, the reader hardly knows it. In this paper, we propose a tag cognizance scheme based on framed and slotted ALOHA, which is characterized by directly taking a Bayes action on the number of slots without estimating the number of tags separately. Specifically, a Bayes action is yielded by solving a decision problem which incorporates the prior distribution the number of tags, the observation on the number of slots in which no tag responds and the loss function reflecting the cognizance rate. Also, a Bayes action in each frame is supported by an evolution of prior distribution for the number of tags. From the simulation results, we observe that the pair of evolving prior distribution and Bayes action forms a robust scheme which attains a certain level of cognizance rate in spite of a high discrepancy between the Due and initially believed numbers of tags. Also, the proposed scheme is confirmed to be able to achieve higher cognizance completion probability than a scheme using classical estimate of the number of tags separately.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.05a
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• pp.866-869
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• 2013

In this Paper, I propose a new anti-collision algorithm called Arbitrator-collision free reflected frame which restricts the size of frames and controlled the frame size when there are small tags. Since the proposal algorithm keeps the frame size and controlled the number of responding tags in such a way ones. can increase slot utilization, the algorithm shows superior performance to the existing algorithms. The simulation results showed that the proposed algorithm improves the efficiency by 0.8times compared to the existing algorithm.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.6
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• pp.29-36
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• 2016

A wireless passive sensor network is a network which, by letting separate RF sources supply energy to sensor nodes, is able to live an eternal life without batteries. Against expectations about an eternal life, however, a wireless passive sensor network still has many problems; scarcity of energy, non-simultaneity of energy reception and data transmission and inefficiency in resource allocation. In this paper, we focus on a wireless passive sensor network providing a packet service which is tolerable to packet losses but requires timely delivery of packets. Perceiving the practical constraints, we then consider a contending-type MAC scheme, rooted in framed and slotted ALOHA, for supporting many sensor nodes to deliver packets to a sink node. Next, we investigate the network-wide throughput achieved by the MAC scheme when the packets transmitted by geographically scattered sensor nodes experience path losses hence capture phenomena. Especially, we derive an exact formula of network-wide throughput in a closed form when 2 sensor nodes reside in the network. By controlling design parameters, we finally optimize the contending-type MAC scheme as to attain the maximum network-wide throughput.

• ETRI Journal
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• v.30 no.5
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• pp.653-662
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• 2008

Arbitration of tag collision is a significant issue for fast tag identification in RFID systems. A good tag anti-collision algorithm can reduce collisions and increase the efficiency of tag identification. EPCglobal Generation-2 (Gen2) for passive RFID systems uses probabilistic slotted ALOHA with a Q algorithm, which is a kind of dynamic framed slotted ALOHA (DFSA), as the tag anti-collision algorithm. In this paper, we analyze the performance of the Q algorithm used in Gen2, and analyze the methods for estimating the number of slots and tags for DFSA. To increase the efficiency of tag identification, we propose new tag anti-collision algorithms, namely, Chebyshev's inequality, fixed adjustable framed Q, adaptive adjustable framed Q, and hybrid Q. The simulation results show that all the proposed algorithms outperform the conventional Q algorithm used in Gen2. Of all the proposed algorithms, AAFQ provides the best performance in terms of identification time and collision ratio and maximizes throughput and system efficiency. However, there is a tradeoff of complexity and performance between the CHI and AAFQ algorithms.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.9
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• pp.29-36
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• 2010

Consider an RFID network configured as a star such that a single reader is surrounded by a crowd of tags. In the RFID network, prior to attaining the information stored at a tag, the reader must cognize the tags while arbitrating a collision among tags' responses. For this purpose, we present a tag cognizance scheme based on framed and slotted ALOHA, which statically provides a number of slots in each frame for the tags to respond. For the evaluation of the cognizance performance, we choose the cognizance completion probability and the expected cognizance completion time as key performance measures. Then, we present a method to numerically calculate the performance measures. Especially, for small numbers of tags, we derive them in a closed form. Next, we formulate a problem to find an optimal time structure which either maximizes the cognizance completion probability under a constraint on the cognizance time or minimizes the expected cognizance completion time. By solving the problem, we finally obtain an optimal number of slots per frame for the tags to respond. From numerical results, we confirm that there exist a finite optimal number of slots for the tags to respond. Also, we observe that the optimal number of slots maximizing the cognizance completion probability tends to approach to the optimal number of slots minimizing the expected cognizance completion time as the constraint on the cognizance time becomes loose.