• Journal of information and communication convergence engineering
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• 제10권3호
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• pp.242-247
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• 2012

In the determination of suitable frame sizes associated with dynamic framed slotted Aloha used in radio frequency identification tag identification processes, the widely imposed constraint $L=2^Q$ often yields inappropriate values deviating far from the optimal values, while a straightforward use of the estimated optimal frame sizes causes frequent restarts of read procedures, both resulting in long identification delays. Taking a trade-off, in this paper, we propose a new method for determining effective frame sizes where the effective frame size changes in a multiple of a predetermined step size, namely ${\Delta}$. Through computer simulations, we show that the proposed scheme works fairly well in terms of identification delay.

• 한국통신학회논문지
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• 제39B권9호
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• pp.598-605
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• 2014

본 논문에서는 능동형 RFID 시스템용 고속 태그 수집을 위한 개선된 알로하 알고리즘을 제안하고, 이를 TI사의 CC2530 칩을 사용하여 태그와 리더기 각각의 기능을 구현하여 시험함으로써 그 성능을 증명하였다. 기존의 ISO/IEC 18000-7 등의 능동형 RFID 규격에서 제시하고 있는 태그 수집 알고리즘에서는 리더기와 태그의 통신이 성공적으로 종료된 후 리더기가 각 태그들에게 별도의 슬립 명령을 전송하는 반면, 제안된 방식에서는 통신이 종료된 태그들은 두 번째 명령어를 확인한 후 즉시 슬립 모드로 진행할 수 있도록 함으로써 리더기의 태그 수집 시간을 대폭 감소시켰다. 리더기와 태그를 구현하여 시험한 결과 30개의 태그가 평균 400 ms 이내에서 모두 인식되었으며, 1초 이내에 인식되는 인식률은 99.7% 이상임을 확인하였다. 리더기와 태그 간의 거리가 2m 이내인 경우 태그는 100% 인식되었으며, 2.5m 이내인 경우와 3m 이내인 경우 초당 인식 확률이 각각 99.94%와 99.7%였다. 각 거리의 경우를 평균하여 99.91%로 나타남으로써 실제 현장에의 적용 가능성을 보였다.

• Journal of information and communication convergence engineering
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• 제6권4호
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• pp.364-369
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• 2008

The FSA algorithm for identifying multiple tags in RFID systems is based on the slotted ALOHA scheme with a fixed frame size. The performance of FSA algorithm is dependent on the frame size and the number of tags in the reader's identification range. Therefore, this paper proposes a new ODFSA. The proposed ODFSA algorithm dynamically allocates the optimal frame size at every frame based on the number of tags in the reader's identification range. According to the simulation results, the system efficiency of the proposed algorithm should be maintained optimally. Also, the proposed algorithm always obtained the minimum tag identification delay.

• 전기학회논문지
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• 제59권11호
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• pp.2103-2107
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• 2010

This paper deals with the recognition of multiple mobile robots equipped with RFID tag. In the case that the number of robots recognized by each RFID reader is larger than that of allocated slots, the clashing recognition occurs. And, in the case that the total number of robots recognized by all RFID reader is larger than that of real robots, the repetitious recognition occurs. We employ the dynamic frame slot allocation by using the ALOHA algorithm to prevent the clashing recognition and estimate the number of robots by using the received signal strength indication to prevent the repetitious recognition. The numerical experiment shows the reliability and the efficiency of the proposed method.

• Journal of information and communication convergence engineering
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• 제5권3호
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• pp.181-184
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• 2007

In this paper, a CSSMA/AI MAC protocol in packet CDMA network is presented. The main features of this protocol are the code status sensing and reservation for reducing the packet collision. The base station broadcasts the code status on a frame-by-frame basis just before the beginning of each preamble transmission, and the mobile station transmits a preamble for reserving a code based on the received code status. After having transmitted the preamble, the mobile station listens to the downlink of the selected code and waits the base station reply. If this reply indicates that the code has been correctly acquired, it continues the packet transmission for the rest of the frame. If there are other packets waiting for transmission, the base station broadcasts the status of the code as reserved, and the mobile station transmits a packet on a reserved code for the successive frames.

• 대한전자공학회논문지TC
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• 제48권2호
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• pp.21-28
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• 2011

Tag가 reader 주변을 정상적으로 오가는 별 형태의 RFID 망을 고려한다. 이 RFID 망에서 주위의 tag를 인식하기 위해 동적으로 프레임에 속한 슬롯의 수를 결정하는 동적 프레임화 및 슬롯화된 ALOHA 기반의 방식을 제안한다. 이 tag 인식 방식은 특징적으로 주위의 tag의 기대 수를 추정하기 위해 R-회고풍 최대 우도 규칙이라 불리는 규칙을 채택하여 이전 R 개의 프레임에서 얻은 관찰 값을 tag의 기대 수의 우도를 최대화하는 과정에 사용한다. 모의 실험 결과는 회고의 깊이를 조금 늘려도 인식 성능이 유의할 만큼 향상됨을 보여준다.

• 산업공학
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• 제22권3호
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• pp.278-286
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• 2009

The anti-collision algorithms to identify a number of tags in real-time in RFID systems are divided into the anti-collision algorithms based on the Framed slotted ALOHA that randomly select multiple slots to identify the tags, and the anti-collision algorithms based on the Tree-based algorithm that repeat the questions and answer process to identify the tags. In the hybrid algorithm which is combined the advantages of these algorithms, tags are distributed over the frames by selecting one frame among them and then identified by using the Query tree frame by frame. In this hybrid algorithm, however, the time of identifying all tags may increase if many tags are concentrated in a few frames. In this study, to improve the performance of the hybrid algorithm, we suggest an improved algorithm that the tags select a specific group of frames based on the earlier bits of the tag ID so that the tags are distribute equally over the frames. By using the simulation and mathematical analysis, we show that the suggested algorithm outperforms traditional hybrid algorithm from the viewpoint of the number of queries per frame and the time of identifying all tags.

• Journal of Communications and Networks
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• 제14권1호
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• pp.34-39
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• 2012

Collisions between tags greatly reduce the identification speed in radio frequency identification (RFID) systems and increase communication overhead. In particular for an active RFID system, tags are powered by small batteries, and a large number of re-transmissions caused by collisions can deteriorate and exhaust the tag energy which may result in missing tags. An efficient collision-free arbitration protocol for active RFID systems is proposed in this paper. In this protocol, a new mechanism involving collision detection, collision avoidance, and fast tag access is introduced. Specifically, the pulse burst duration and busy-tone-detection delay are introduced between the preamble and data portion of a tag-to-reader (T-R) frame. The reader identifies tag collision by detecting pulses and transmits a busy tone to avoid unnecessary transmission when collision occurs. A polling process is then designed to quickly access the collided tags. It is shown that the use of the proposed protocol results in a system throughput of 0.612, which is an obvious improvement when compared to the framed-slotted ALOHA (FSA) arbitration protocol for ISO/IEC 18000-7 standard. Furthermore, the proposed protocol greatly reduces communication overhead, which leads to energy conservation.

• ETRI Journal
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• 제39권4호
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• pp.546-557
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• 2017

In a long term evolution-advanced (LTE-A) system, the traffic overload of machine type communication devices is a challenge because too many devices attempt to access a base station (BS) simultaneously in a short period of time. We discuss the challenge of the gap between the theoretical maximum throughput and the actual throughput. A gap occurs when the BS cannot change the number of preambles for a random access channel (RACH) until multiple numbers of RACHs are completed. In addition, a preamble partition approach is proposed in this paper that uses two groups of preambles to reduce this gap. A performance evaluation shows that the proposed approach increases the average throughput. For 100,000 devices in a cell, the throughput is increased by 29.7% to 114.4% and 23.0% to 91.3% with uniform and Beta-distributed arrivals of devices, respectively.

• 대한전자공학회논문지TC
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• 제45권5호
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• pp.12-20
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• 2008

RFID(Radio frequency identification) 기술은 어떤 사물에 부착되는 태그(Tag)의 고유정보를 리더(Reader)를 사용하여 비접촉 방식으로 식별하는 기술로, 현재 유비쿼터스 센서 네트워크(Ubiquitous Sensor Network) 구현의 핵심기술로 고려되고 있다. 특히 유통 물류분야에 적용되는 UHF대역 RFID시스템은 리더가 인식해야 할 태그의 수가 상당히 많아 태그충돌(Tag-collision)이라는 부정적인 영향이 발생하고, UHF대역 RFID기술 표준인 EPCglobal Gen2 protocol에서는 이런 태그충돌을 해결하기 위해 Slotted Random Anti-collision algorithm을 제시하고 있다. 본 논문에서는 이런 태그충돌의 영향을 최소화하고 전체 시스템의 효율을 보다 향상시키기 위하여 주어진 환경에 유동적으로 리더의 신호 전송전력을 조절하는 전력상승기법(Power Increasing Method)을 제안하고 그것을 주어진 환경에 동적으로 적용함으로써 Gen2에서 제시한 알고리즘보다 개선된 성능을 검증하였다.