Frame Slotted Research Articles

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.

Multiple-bits-slot reservation aloha protocol for tag identification

The Radio Frequency Identification (RFID) system consists of a reader and many tags. In the mobile RFID environment, consumers can obtain product-related information of tags by using readers which are installed in mobile phones. However, the tag collision problem is serious in this environment. This paper proposes a multiple-bits-slot reservation aloha protocol for handling this problem. In the protocol, the reader assigns reservation slots before allocating frame slots, and each tag generates a random sequence in its own reservation slot randomly selected by this tag to reserve a frame slot, then the reader efficiently captures the reservation collisions in reservation slots by Manchester coding. Accordingly, the protocol significantly reduces collision frame slots, and eliminates empty frame slots. Our performance evaluation shows that the proposed protocol outperforms other aloha-based protocols <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> .

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.

An Improved Accelerated Frame Slotted ALOHA (AFSA) Algorithm for Tag Collision in RFID

The efficiency of tag identification in an RFID system can be low down due to the tag collision problems. the tag collision problem occurs when a reader try to read multiple tags in an interrogation zone. as a result the reader does not identify the tag correctly. that causes a loss of information or data interference. to solve such kind of issues a series of aloha based algorithm and binary search algorithm have beed proposed. the most simple popular and good giving performance algorithm are aloha based anti-collision algorithms. in this paper we present a new variation in accelerated slotted aloha afsa. our proposed algorithm by using the bitmaps and avoids wastages in bit times due to idleness and collided slots reduce the tag reading time. the simulation result shows that afsa can significantly reduce the average tag reading time with respect to the base protocols and achieve high tag reading rates under both static and mobile setting.

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

Collision Reduction Using Modified Q-Algorithm with Moving Readers in LED-ID System

LED-ID (Light Emitting Diode - Identification) is one of the key technologies for identification, data transmission, and illumination simultaneously. This is the new paradigm in the identification technology environment. There are many issues are still now challenging to achieve high performance in LED-ID system. Collision issue is one of them. Actually this is the most significant issue in all identification system. LED-ID system also suffers from collision problem. In our system, collision occurs when two or more readers transmit data to tag at the same time or vice versa. There are many anti-collision protocols to resolve this problem; such as: Slotted ALOHA, Basic Frame Slotted ALOHA, Query Tree, Tree Splitting, and Q-Algorithm etc. In this paper, we propose modified Q-Algorithm to resolve collision at tag. The proposed protocol is based on Q-Algorithm and used the information of arrived readers to a tag from neighbor. The information includes transmitting slot number of readers and the number of readers that can be arrived in next slot. Our proposed protocol can reduce the numbers of collision slot and the successful time to identify all readers. In this paper our simulation and theoretical results are presented.

AN EFFICIENT LOAD BALANCING CLUSTERING SCHEME FOR DATA CENTRIC WIRELESS SENSOR NETWORKS

Clustering is an efficient approach to capitalize the energy of energy constraint sensor nodes in wireless sensor networks. Clustering schemes do not guarantee formation of clusters with equal number of nodes. So data frames transmitted by the nodes vary. TDMA schedule of nodes of smaller cluster is smaller than others that results more number of data frames and hence more energy consumption. The non uniform energy consumption of nodes affects the load balancing of network and these nodes are more prone to die earlier than others. In this paper, an improved scheme for cluster head selection is proposed. Clusters having variable frame slots for nodes are applied to E-LEACH and improved E-LEACH to make the cluster more load balanced. Simulation is carried out in NS-2 to analyze the performance of E-LEACH and improved E-LEACH with variable frame length. Variable frame slot scheme for clusters is also measured with the varying distance of base station from the field. Simulation results show that clustering with variable frame length has an improvement of 7% in node death rate over E-LEACH and an improvement of 9% in node death rate over improved ELEACH. Results suggest that variable frame length scheme improves the performance of clustering schemes for WSNs and have most significant result at base station located at 75m from the field.

Multiframe Maximum-Likelihood Tag Estimation for RFID Anticollision Protocols

Automatic identification based on radio frequency identification (RFID) is progressively being introduced into industrial environments, enabling new applications and processes. In the context of communications, RFID rely mostly on Frame Slotted Aloha (FSA) anticollision protocols. Their goal is to reduce the time required to detect all the tags within range (identification time). Using FSA, the maximum identification rate is achieved when the number of contending tags equals the number of contention slots available in the frame. Therefore, the reader must estimate the number of contenders and allocate that number of slots for the next frame. This paper introduces the new MFML-DFSA anticollision protocol. It estimates the number of contenders by means of a maximum-likelihood estimator, which uses the statistical information from several frames (multiframe estimation) to improve the accuracy of the estimate. Based on this expected number of tags, the algorithm determines the best frame length for the next reading frame, taking into account the constraints of the EPCglobal Class-1 Gen-2 standard. The MFML-DFSA algorithm is compared with previous proposals and found to outperform these in terms of (lower) average identification time and computational cost, which makes it suitable for implementation in commercial RFID readers.

Dynamic system model for optimal configuration of mobile RFID systems

In many practical RFID applications tags are attached to items that pass through the reader’s field moving at a constant speed, following a fixed path. The time-constrained presence of the tags in the identification region introduce the possibility that tags exit the system without being identified ( lost tags). Reliability is a practical requirement in most applications, which implies that the portion of lost tags should be kept below a very small threshold. Therefore, we take this fact as the starting point in the design process. We present a mathematical model for RFID systems implementing Frame Slotted Aloha as the collision resolution protocol. Upon this model it is possible to compute the tag loss ratio and therefore to obtain the optimal frame size in terms of reliability. While previous works generally use a Markovian approach, our model is based on dynamic systems theory, having a smaller computational cost which, in addition, is independent of the dimension of the system. Moreover, the proposed model allows us to identify the multiplicity of the equilibrium points in the system, an interesting and relevant property that has been overlooked in RFID systems so far. Finally, we present a design procedure based on our model that allows to configure the physical parameters of the system in order to adjust both the throughput and the reliability.

On the optimal frame-length configuration on real passive RFID systems

The majority of the anti-collision protocols proposed for passive RFID systems are based on frame slotted aloha (FSA). They assume a classical result in FSA-based protocols which states that the theoretical identification throughput is optimized when the number of competing tags in coverage equals the number of slots in the frame. However, this is not exact in real RFID systems, as the so-called capture effect is neglected. The capture effect occurs when a tag identification signal is successfully decoded from a collision slot. This paper analyzes the identification performance of real RFID systems, taking into account not only the capture effect, but also the requirements imposed by the de facto standard EPCglobal Class-1 Gen-2. The analysis is addressed by discrete time Markov chains. From the analysis, a set of relevant results is extracted: the frame-length values that, configured into the readers studied, guarantee the best identification performance (maximum throughput). The analytical results have been confirmed by means of simulations and by a set of measurements performed on a real passive RFID system. Results closely match the analysis predictions, which demonstrate a notable impact of the configuration on the performance.

A Recognition System for Multiple Mobile Robots Using RFID System in Smart Space

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.

QTDFS-ALOHA

Proposed protocols work clumsily in resolving the collisions occurred in dense RFID tag environment. QTDFS-ALOHA, a hybrid protocol which combines the query tree protocol and the dynamic frame slot ALOHA protocol, is proposed. In each frame of this protocol, only tags in the active set are allowed to answer in randomly selected slots. Afterwards, the population of tags in the active set is estimated. According to the identification accuracy required, the protocol may choose to continue the identification of the active set with delicately calculated frame length, or to divide the active set into multiple subsets using some binary prefix strings and identify each subset subsequently in the following frames. This process is performed recursively for all tag sets until the required accuracy is achieved. Proposed tag population estimation methods are summarized and evaluated. Numeric simulation verifies that this hybrid protocol outperforms other frame slot ALOHA based protocols.

Optimal frame size analysis for framed slotted ALOHA based RFID networks

We offer an analytical solution for the optimal frame size of the non-muting version of the Basic Frame Slotted ALOHA collision resolution protocol for RFID networks. Previous investigations of RFID frame size have been empirical and have not yielded a general result. Our theoretical analysis provides a generalized result. Our solution can be used to determine the optimal frame size for any given number of RFID tags. Suboptimal selection for the frame size can result in substantially longer than minimum census delays and can unnecessarily increase energy consumption. We were able to demonstrate about 20% performance improvement in reduced census delay for a given range of values. Our results can help speed-up reader-side processing times, lower the implementation complexity of RFID readers, and increase their energy efficiency.

A Hybrid Collision Resolution Protocol for Passive RFID Tag Identification

Wireless communication channel collision of RFID system is a key issue that affects the pervasive application of the system, especially for passive RFID system due to the constrained communication ability and energy supply of tags. The collision resolution protocols suggested can be categorized into deterministic tree based protocols and probabilistic frame slot ALOHA based protocols. A hybrid protocol, which combines the query tree protocol and dynamic framed slotted ALOHA protocol, is presented here. In this protocol, at the beginning of each identification frame, the reader broadcasts a query command message which contains a suffix string and integer to indicate a frame size used in this frame to all tags in its vicinity, and every tag whose data match the specified suffix string randomly selects a slot in the frame to transmit its data to the reader. After each round, based on the different occupying situation of slots, the reader re-estimates the number of tags in its range, and according to the identification accuracy required, decides whether to split the group of tags to be identified into sub-groups or not, and adjust the suffix string and select a suitable frame size for the command messages of the following frames. Through this repeated identification and division process, the RFID tags can be identified within a number of frames. Some key factors that influence the efficiency of the identification are also discussed based on binomial distribution model. Three methods for the tag population estimation are examined and their accuracies are compared, and the optimum frame size for the identification of different number of tags is given in consideration of the throughput and efficiency. To verify the performance of the hybrid protocol, a numeric simulation is performed, in which 100 groups of SGTIN-96 encoded tags are generated randomly. Simulation shows that this hybrid protocol outperforms other frame slot ALOHA based collision resolution protocols, especially when there are a large number of RFID tags to be identified. The overall throughput of the hybrid protocol is kept around 34.8% when there are more than 40 tags, near the theoretical maximum value 36.8%. A linear relationship between the number of tags and the total frames and slots required is also observed in the numeric simulation.

A framework for fast RFID tag reading in static and mobile environments

A framework for reducing the average reading time of passive RFID tags in dense environments is introduced. The proposed framework termed Accelerated Frame Slotted ALOHA (AFSA) can be used in conjunction with almost all RFID tag reading protocols that are based on frame slotted ALOHA. It is shown that AFSA reduces the tag reading time by avoiding the wastage in bit times due to collisions and idle slots. The implementation of AFSA in conjunction with two different ALOHA protocols – one with unlimited frame sizes and the other with limited frame sizes is discussed. For both these protocols, extensions of AFSA to read passive tags in a mobile setting are described. Simulation results show that AFSA reduces the average tag reading time by up to 40% with respect to the stand alone ALOHA protocols under both static and mobile settings.

Easy definition of new facets in the frame-based language Objlog+

This article aims at presenting a method that allows to extend frame-based languages at the level of their facets, in the framework of a language called Objlog+. First, we describe the different methods classically used to create new facets and show their limitations. We then propose our facet definition method which keeps them their status of descriptive elements within slots. Its fundamental principle consists in representing every facet by means of a frame which contains its properties as well as the knowledge allowing our language to manage the control structure of this facet automatically at the moment one of its occurrences within a frame slot is accessed. For that purpose, the facet notion has been first analyzed systematically in order to extract its main characteristics.

PERFORMANCE EVALUATION OF A REQUEST-TDMA/CDMA PROTOCOL FOR WIRELESS NETWORKS

This paper proposes a new medium access control (MAC) protocol, called Request-TDMA/CDMA, for supporting multimedia traffic in wireless networks. In this hybrid protocol, CDMA (code division multiple access) is laid over TDMA (time division multiple access), where a time frame has two kinds of slots, namely data slots and control slots. The data slots are used to the user to transmit their data while the control slot holds the information for the next frame's slot allocation. Each data slot in a frame can be simultaneously used by multiple users with the help of uniquely assigned codes. Whenever a user needs to transmit a message, he first sends a request message to the central controller and enters the contention process. The controller takes into consideration the time of generation of a call, the bit rate requirement and the message length while reserving slots for the entire length of the message generated. The user then goes into the transmission phase if he is successful in the contention process, and continues to transmit his data till the entire message is sent. Three scheduling algorithms for the allocation of data slots are proposed and their performance are studied for four classes of traffic. We also analyze our protocol using a two-dimensional Markov chain model, and compute the state transition probabilities and derive the average waiting time for a given system load. By simulation experiments we show that our request-TDMA/CDMA protocol is able to effectively combine the orthogonality of both time and code division multiplexing. Further enhancements are also proposed to decrease the waiting time and increase the average channel utilization.

Generalizing case frames using a thesaurus and the MDL principle

A new method for automatically acquiring case frame patterns from large corpora is proposed. In particular, the problem of generalizing values of a case frame slot for a verb is viewed as that of e...

Structured Image Retrieval

Most image-retrieval systems rely on similarity measures for collecting images ofsimilartypes. Similarity measures are an integral part in the development of image management systems. In this paper, we propose frame-based similarity measures for accessingstructuredimages, e.g. images can be understood by inferring from objects present and the relationships among them. The image content is described in the following ways: (1) adjacency blocks and/or (2) unary and binary attributes that are used to fill frame slots for representing image structures. The retrieval is based on similarity measures by comparing the contents of the query image and database image. The frame-based representation scheme is application-independent. Our similarity measures allow for images to be retrieved with different degrees of similarity and are flexible. We have developed a prototype system using the paradigms proposed. We demonstrate the usefulness of our system with some experimental results.

Method for block synchronisation in optical PPM

A method for block synchronisation in optical PPM is proposed. This method is an application of the synchronisation method for PN sequences normally used in spread spectrum communication systems. In this method, the phase of the synch signal is shifted little by little, with the synch decision process carried out on the receiving side until synchronisation is attained. The decision rule is based on the fact that the number of received pulses in each frame of the synch signal must be one and that the time when the pulse is received should not be in the pre-fixed prohibited frame slot, provided that synchronisation is established. This method&apos;s synchronisation characteristics are investigated, and it is shown that block synchronisation can be established sufficiently with only 12.5% of additional prohibited slots.