Dynamic Framed Slotted ALOHA Research Articles

Improvement of RFID Tag Anti-Collision Algorithm Based on the Dynamic Framed Slotted ALOHA

본 논문에서는 DFSA (Dynamic Framed Slotted ALOHA) 기반 충돌 방지 알고리즘에 대해 논하고, 개선된 태그 충돌 방지 알고리즘을 제안한다. 제안된 방법은 기대 값을 이용하는 방법으로서 한 번의 연산을 통해 측정값에 근접한 기대 값을 갖는 태그 수를 추정하므로 속도가 빠르다는 장점이 있으며 태그 수에 따른 빈 슬롯 개수 및 충돌 슬롯의 개수를 이용하여 기대 값을 구한 후 실제 태그 개수를 추정할 수 있다. 제안된 알고리즘은 시뮬레이션을 통해 기존 방법과 비교 및 분석하였다. 그 결과, 전체 태그에 대하여 평균 18.8 라운드에 모든 태그를 식별하였다. 태그의 수가 1000개 이하일 경우 평균 18.2 라운드에 모든 태그를 식별하였으나 태그 수가 1000개 이상인 경우 19.2 라운드에 태그를 식별하였다. 제안된 방식 및 기존 방식을 비교하였을 때 평균 태그 수에 따른 라운드 수가 상쇄 기법이 적용된 DFSA 방식보다 3.1 %, DFSA 방식보다 10.1 %, FSA (Framed Slotted ALOHA) 방식보다 37.5 % 가량 감소하여 처리 속도가 향상됨을 확인할 수 있었다. 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).

An Enhanced Posterior Probability Anti-Collision Algorithm Based on Dynamic Frame Slotted ALOHA for EPCglobal Class1 Gen2

In a Radio Frequency Identification (RFID) System, collision between tags is one of the core problems that we must consider about. In general, a collision will occur when more than one tag communicates with the reader simultaneously, reducing the system efficiency. To solve this, dynamic frame slotted ALOHA (DFSA) is widely adopted nowadays, and as a variant of DFSA algorithm, Q-algorithm is accepted by the EPCglobal specifications for RFID air interface Class1 Gen2 protocol. Based on this, we provide a new algorithm called EPP-Q to adjust the parameter Q more accurate as well as maintain high system efficiency when tags are no more than 21(Q belongs to 0 to 15). The simulation provides an obvious improvement when EPP-Q is compared with other two mainstream algorithms, not only in system efficiency, but also in the quantity of time slots used.

RFID Technology and Applications

RFID is emerging as one of most fundamental technologies to Internet of Things due to its attractive features such as good reading ranges, high data rates, and low cost. RFID has achieved a widespread success in various applications, ranging from asset tracking, highway toll collection, supply chain management, animal identification to surveillance systems. Moreover, there has been a wide scope of development in RFID standards, protocols, and middleware. However, a series of challenging issues should be properly addressed before a massive adaptation of RFID technology. In this special issue, we have received 24 paper submissions and accepted 9 papers finally according to the reviewers’ comment and associate editors’ suggestion. These accepted papers include RFID reader antenna design, RFID tag antenna design, RFID passive transponders, tag collision algorithm, and RFID application systems. B. Lee et al. from Kwangwoon University of Korea proposed a novel structure of an NFC loop antenna for mobile handset applications by improving the performance of an NFC loop antenna when a ferrite-polymer composite is attached between the embedded NFC loop antenna and the phone battery. The proposed loop antenna gives better performance than that of a conventional NFC loop antenna. L. X. Zheng et al. from South China University of Technology proposed a compact RFID reader antenna for UHF near-field and far-field operations. The structure of the antenna is a novel folded-dipole loop and is formed by a concentric metal ring with a split. It can provide uniform magnetic near-field distribution and available farfield gain. Y. Yao et al. from Beijing University of Posts and Telecommunications also proposed a novel RFID reader antenna. This antenna was fabricated using indium tin oxide film; thus, it has optically transparent characteristic.This kind of antenna can be used in clothing stores. P. Jankowski-Mihulowicz et al. from Rzeszow University of Technology proposed novel RFID passive transponders with additional energy harvester. They can recover energy from the electromagnetic field of read device and the harvested energy was utilized to supply a microprocessor acquisition block for developed LTCC pressure sensor. C. Wang et al. from Beijing University of Posts and Telecommunications proposed an advanced dynamic framed-slotted ALOHA algorithm based on Bayesian estimation and probability response to solve the tag collision problem of RFID system. The simulation results show that the proposed algorithm has better performance. We sincerely hope that this special issue can further help the readers to understand RFID antenna design and applications and explore the future development of the system.

Assigned Tree Slotted Aloha RFID Tag Anti-Collision Protocols

With the development of radio frequency identification (RFID) technology, RFID systems have been used in various applications. But the tag collision problem greatly affects the performance of many RFID systems, especially in large scale tag identification environments. In this paper, we propose two new efficient tag anti-collision protocols, i.e., the assigned tree slotted Aloha (ATSA) protocol and the improved ATSA (ImATSA) protocol based upon Manchester encoding. The key technology is to apply the prefix matching idea to the dynamic frame slotted Aloha identification model by assigning a unique ID prefix to each frame and slot. Both theoretical and simulation results indicate that ImATSA can achieve an average system efficiency of around 58%.

An ALOHA-based improved anti-collision algorithm for RFID systems

Tag collision arbitration is considered as one of the critical issues in RFID system design. In order to further improve the identification efficiency of tag anti-collision algorithms in RFID systems, several types of dynamic framed slotted ALOHA (DFSA) anti-collision algorithms are analyzed, and a new anti-collision algorithm is proposed. The proposed algorithm has the ability of identifying the time slot distribution which is selected by the tags within a reader's interrogation range in advance. Then the free time slots will be skipped when the reader queries each time slot. Also, the colliding tags will be immediately processed with additional time slots. Simulation results show that the proposed algorithm takes fewer total number of time slots and has a higher efficiency of tag identification compared to the other four DFSA anti-collision algorithms.

A Kind of Enhanced Slotted ALOHA Algorithm for Anti-Collision in RFID System

in the RFID system, the conflict caused by the multi-label has been affecting system performance. This paper proposed a grouping dynamic framed slotted ALOHA algorithm based on the analysis of ALOHA algorithm. According to the conflict situation, to make real-time estimates the number of tags on the dynamic framed slotted ALOHA algorithm from the mathematical point of view, Dynamically change the frame length or the labels are grouped to reduce the label probability of collisions, thereby improving the efficiency of the recognition.

Improved RFID Anti-Collision Algorithm Based on Dynamic Framed Slotted ALOHA Algorithm

Aiming at the problem of tag conflict in the RFID system, an improved algorithm based on dynamic framed slotted ALOHA algorithm is proposed. In this algorithm , when the recognition of a frame length is still not finished, according to the existing conflict timeslot and free timeslot inside of frame, frame length can adjusted in advance, furthermore a new frames recognition process is began, which can improve the recognition efficiency of the existing algorithm, increase throughput. The performance simulation experiment shows that the improved algorithm has more advantage than dynamic slotted ALOHA algorithm.

A Fast and Accurate Tag Estimation Algorithm for Dynamic Framed-Slotted ALOHA Based on M/D/1 Queue in RFID Systems

A novel tag estimation algorithm named DFSA-MD1 is proposed, and applied to the field of tag identification that aims at decreasing tag collision number in RFID systems. The proposed algorithm regarded the tag identification process of a frame of the dynamic frame slotted ALOHA algorithm (DFSA) as an M/D/1 queuing system. The reader can estimate tag number of next frame from success slots number and collision slot number in current frame and current frame size according to M/D/1 queuing model.The experimental results show that DFSA-MD1 algorithm requires less time consumption and lower complexity for tag identificaiton and achieves the best performance of the DFSA tags identification protocols.

Grouping Based Dynamic Framed Slotted ALOHA for Tag Anti-Collision Protocol in the Mobile RFID Systems

Dynamic framed slotted ALOHA (DFSA) protocol has been widely used in many RFID systems. According to the informa- tion from last frame (e.g. the number of idle, success and collision slots) , DFSA dynamically adjusts the next frame size so as to reach higher identification efficiency. The process is known as tag estimation of D FSA. Similar to most existing tag anti-collision protocols, The DFSA initially aims at tag identification in static environments where all tags ke ep still during the tag identification process. How- ever, in many real scenarios (called mobile RFID systems), tags usually move along a fixed path in the reader coverage area. That is, tags enter and leave the area continuously. This easily leads to serious errors of tag estimation because the tag estimation of almost existing DFSA variants do not consider new arrival tags. The errors in turn cause very low tag identification rate and eventually make some tag leave the area unidentified. In this paper, we propose a grouping based dynamic framed slotted ALOHA protocol (GBDFSA) which is very suitable for mobile RFID systems. Through tag grouping in their arrival time order, the tag estimation algorithm in GBDFSA can eliminate the influence of new arrival tags. Simulation results show that GBD FSA can significantly reduce the numbers of lost tags in mobile RFID systems. The idea of the paper is used in various existing DFSA variants so as to make these protocols adapt to mobile RFID systems.

Forward Predicting and Backward Verifying Tags Number Estimation in RFID System

Tag collision happens when multiple tags are energized simultaneously, reflect their respective signals back to the reader at the same time, and the reader is unable to differentiate these signals. This problem causes decrease of the RFID efficiency especially in the tag-intensive RFID system. The dynamic frame slotted aloha (DFSA) algorithm is the most appropriate solution for this problem, which is based on an accurate tags number estimate method. A novel forward predicting and backward verifying adaptive precise tags number estimation algorithm is proposed in this paper. Experiment results show that it is more effective than others.

An Enhanced Collision Detection Scheme for ISO 18000–6C RFID Systems

In radio-frequency identification systems, tag collision resolution is a significant issue for fast tag identification. Dynamic framed slotted ALOHA (DFSA) is one of the most widely used algorithms to resolve tag collision. Collision detection (CD) plays an important role in determining the efficiency of DFSA-based algorithms because most DFSA-based algorithms determine the next frame size according to the number of collided slots in the current frame. Existing CD methods do not respond quickly enough to detect a collision and have difficulty in distinguishing a collision from noise, resulting in a degradation of system efficiency. This paper presents a CD scheme based on the ISO/IEC 18000–6C protocol to improve CD efficiency. This scheme enables fast and accurate CD by detecting the number of pulses transmitted by tags. The effectiveness and practical feasibility of the scheme is verified by simulation and implementation. Performance evaluation results show that the proposed scheme achieves faster identification speed than the conventional methods, especially under noise conditions.

A Stochastic Shortest Path Model to Minimize the Reading Time in DFSA-Based RFID Systems

RFID systems implementing Dynamic Frame Slotted Aloha (DFSA) can adjust the number of identification rounds (slots) within an inventory cycle (frame). The usual approach to reduce the identification time of the tag population is to select the frame size attaining the highest throughput in the frame. However, it is more accurate to minimize the identification time of all the tags considering an indefinite long decision horizon. This is done in this paper by means of a Stochastic Shortest Path (SSP) formulation that incorporates capture effect and differentiation among slot durations. Our results show that the optimal policy is even faster than previous approaches.

Dynamic Frame Sizing with Grouping Slotted Aloha for UHF RFID Networks

Tag collision in a radio frequency identification system (RFID) is an important parameter that affects the overall system performance. Different algorithms have been proposed to efficiently utilize the slots during data transmission between reader and tags that need to be identified. Dynamic Frame slotted Aloha is a widely used anti collision algorithm that can be further divided into two main categories depending upon how the frame selection is performed. It has been found that dynamic frame sizing with grouping yields highly efficient results. In this study, the proposed algorithm modifies the mechanism used for dynamic grouping as implemented in the EPC global class 1 generation 2 algorithm and results have been presented showing improvement in the number of slots utilization and iterations required to successfully detect different number of tags. General Terms Algorithms, RFID Anti collision

Reducing tag collision in radio frequency identification systems by using a grouped dynamic frame slotted ALOHA algorithm

In a radio frequency identification system, designing a tag anti-collision algorithm with good performance is the key to improving the system throughput. In this paper, we propose a principle of dynamic frame size regulation and a method of tag grouping, and design a novel algorithm called grouped dynamic framed slotted ALOHA (GDFSA) through combining the above, which first estimates the number of unread tags and divides them into groups, then uses dynamic frame slotted ALOHA in each group. The simulation results show that the proposed algorithm can stabilize the throughput rate between 34.6%-36.8% and the time slots increase linearly in the identification procedure. When the tag number is beyond 2000 compared with conventional algorithms, the proposed algorithm can enhance the slot efficiency by 30%, and optimize the throughput rate obviously and save the system resource.

Anti-Collision Algorithm Analysis of ALOHA-Based RFID

RFID multi-tag identification process of the conflict on the basis of summing up the ALOHA class algorithm put forward an improved dynamic framed slotted ALOHA algorithm. Firstly, this paper uses the improved tag estimation algorithm to estimate the number of tags. Secondly, tag number is determined according to the length of the frame. Finally, tags are divided into several groups when the number of tags greater than the maximum frame length. The simulation results show that the efficiency of the algorithm has been improved obviously.

An Advanced Dynamic Framed-Slotted ALOHA Algorithm Based on Bayesian Estimation and Probability Response

This paper proposes an advanced dynamic framed-slotted ALOHA algorithm based on Bayesian estimation and probability response (BE-PDFSA) to improve the performance of radio frequency identification (RFID) system. The Bayesian estimation is introduced to improve the accuracy of the estimation algorithm for lacking a large number of observations in one query. The probability response is used to adjust responsive probability of the unrecognized tags to make the responsive tag number equal to the frame length. In this way, we can solve the problem of high collision rate with the increase of tag number and improve the throughput of the whole system. From the simulation results, we can see that the algorithm we proposed can greatly improve the stability of RFID system compared with DFSA and other commonly used algorithms.

Accelerating RFID Tag Identification Processes with Frame Size Constraint Relaxation

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 <TEX>$L=2^Q$</TEX> 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 <TEX>${\Delta}$</TEX>. Through computer simulations, we show that the proposed scheme works fairly well in terms of identification delay.

RFID 시스템에서 Hybrid 방식을 이용한 효율적인 충돌 회피 기법

RFID 시스템에서 다수의 태그가 동시에 자신의 ID를 리더기에 전송하게 되면 충돌로 인해 리더기의 태그 인식시간이 지연 된다. 따라서 리더기의 태그 인식시간을 줄이기 위한 효율적인 충돌방지 기술이 필요하다. 본 논문에서는 QT(Query Tree) 방식을 기반으로 DFSA(Dynamic Framed Slotted Aloha) 방식을 추가한 hybrid 충돌 회피 방법에 대해서 제안하고 시뮬레이션을 통하여 기존의 방법과 성능을 비교한다. If multiple Tags in the RFID System transmit their IDs to the Reader at the same time, tag identification time is delayed due to collisions. Therefore, to reduce the reader's identification time, an efficient anti-collision technology is needed. In this paper, we propose a hybrid anti-collision method based on the QT and DFSA. Then, the performances of proposed method are compared with the existing method through extensive simulations.

Maximum a posteriori (MAP)-based tag estimation method for dynamic framed-slotted ALOHA (DFSA) in RFID systems

Radio frequency identification (RFID) is a non-contact technology that uses radio frequency electromagnetic fields to transfer data from a tag attached to an object, for the purposes of automatic identification and tracking. One of the common problems that arise in any RFID deployment is the collision between tags which reduces the efficiency of the RFID system. Dynamic framed-slotted ALOHA (DFSA) is one of the most popular approaches to resolve the tag collision problem. In DFSA, each tag randomly selects one of the time slots of a frame and transmits its data at the slot. Unless the tag successfully transmits its data to a reader, it will try again in the next frame. It is widely known that the optimal performance of framed-slotted ALOHA is achieved when the frame size (i.e., number of time slots) is equal to the number of tags to be identified. So, a reader dynamically adjusts the next frame size according to the number of tags. Thus, it is important to accurately estimate the number of tags. In this article, we propose an accurate maximum a posteriori (MAP)-based tag estimation method with low computational complexity. The idea behind our method is to more accurately determine the most potential number of tags which draws the observed results on the basis of both a posteriori probability and a priori probability. Simulation results show that our method improves the accuracy of tag estimation and the speed of tag identification.

Improved Efficient RFID Tag Estimation Scheme

Dynamic Frame Slotted Aloha) based anti-collision algorithms resolve the collision among the RFID (Radio frequency-ID) tags by adjusting the frame size for the incoming frame according to the number of un-identified tags. The system efficiency directly depends upon the estimated number of tags that contribute towards the frame size adjustment. In this paper, we propose an improved scheme for DFSA which accurately estimates the tags that have to participate in the incoming frame. The scheme also adjusts the incoming frame size according to the estimated tags and keeps the system efficiency very close to the optimal. The simulation results show that for the proposed scheme the tag estimation time and the estimation error rate is far less compared to conventional methods and system efficiency is close to optimal. KeywordsUHF RFID, Tag estimation scheme, EPC global class 1 Gen 2, maximum system efficiency