Won-Ju Yoon

Implementation and performance evaluation of an active RFID system for fast tag collection

Tag collection is one of the major functions in radio frequency identification (RFID) systems. ISO/IEC 18000-7 defines the tag collection algorithm using the anticollision algorithm, based on the framed slotted ALOHA for active RFID systems, but it has efficiency problems that reduce tag collection performance. This paper focuses on improvement of tag collection performance in active RFID systems that comply with ISO/IEC 18000-7. To overcome the efficiency problems and improve tag collection performance we propose two mechanisms: (1) a new slot size decision mechanism to allow the reader to choose the optimum slot size flexibly and (2) a broadcast-based sleep mechanism to put collected tags to sleep effectively. These mechanisms require modification of the standard tag collection algorithm so that they can be readily applied to standard-compliant active RFID systems. We also implemented an active RFID system, composed of an active RFID reader and multiple tags, supporting the modified tag collection algorithm as well as the standard tag collection algorithm. The reader is designed to maximize tag collection performance when the proposed mechanisms are applied. Experimentally, we evaluated the tag collection performance using the reader and 50 tags in the real-world environment. The experimental results show that when two mechanisms are applied and the initial number of slots is chosen appropriately, the performance of the modified tag collection algorithm is greatly enhanced compared with the standard tag collection algorithm: it requires only 945ms for the reader to collect all 50 tags on average, which is 534ms less than the 1479ms taken by the standard tag collection algorithm.

Implementation of a 433 MHz Active RFID System for U-Port

The 433 MHz active RFID system and the E-Seal system are suitable for harbor logistics systems and these systems make possible to build a ubiquitous port where harbor logistics can be managed efficiently. This paper describes the cost-effective implementation of a 433 MHz active RFID system and an E-Seal system which consist of a reader and tags. The reader and tags implemented in this paper comply with relevant ISO standards and have a long communication range. The reader can also retrieve responses of multiple tags simultaneously. Experimental results show the high performance of our implemented systems.

Design and Implementation of an Active RFID System for Fast Tag Collection

Radio frequency identification (RFID) technology is an automatic identification method using radio frequencies between RFID readers and tags. In RFID systems, tag collection is very important issue to collect data from all the tags in reader communication range using anticollision algorithm. There are several researches to develop the efficient anticollision algorithm, but they almost focus on passive RFID systems and show the simulation results. This paper focuses on tag collection in active RFID systems complying with ISO/IEC 18000-7 standard. We propose the modified tag collection algorithm based on the standard and develop an active RFID reader and tags which comply with ISO/IEC 18000-7 and utilize the modified algorithm. As the experiments are achieved with a reader and 30 tags in the real-world environment, the modified algorithm shows better performance of tag collection than the standard algorithm in our active RFID system.

An efficient cooperation of on-demand and proactive modes in Hybrid Wireless Mesh Protocol

Hybrid Wireless Mesh Protocol (HWMP) in IEEE 802.11s provides two routing modes, on-demand and proactive, for WLAN mesh networks. Although the on-demand routing mode always provides the optimum routing paths for data transmission, the initial latency can be very high when communicating with a destination in an external network. On the other hand, the proactive routing mode shows low initial latency when communicating with a destination in an external network, but the data transmission throughput can decrease when communicating with a destination in the same mesh network. This paper proposes an efficient cooperation method of two routing modes, taking advantage of the merits of each routing mode to overcome their faults. To evaluate the performance of the proposed cooperation method, we implemented HWMP on a testbed and performed experiments. The experimental results showed that the proposed cooperation method overcomes the faults of each routing mode and searches for the optimum routing paths quickly and efficiently; it always has the lower initial latency and higher data transmission throughput compared with the on-demand and proactive routing modes.

Multichannel Slotted-Aloha Anticollision Protocol for Active RFID Systems

We propose a multichannel slotted-aloha anticollision protocol to mitigate the tag collision problem and improve tag collection performance in active RFID systems. In the proposed anticollision protocol, while an RFID reader transmits commands to multiple RFID tags via a common radio channel, it receives multiple tag responses over multiple radio channels simultaneously. We also implemented an active RFID system supporting the proposed anticollision protocol. In experiments with the implemented reader and 60 tags, the average time spent on tag collection using the dual-channel anticollision protocol was 46.5% of that required using the single-channel anticollision protocol.

An efficient tag collection algorithm utilizing empty time slots in active RFID systems

We propose an efficient tag collection algorithm utilizing empty time slots in active RFID systems. In the proposed tag collection algorithm, the reader recognizes the existence of empty time slots via carrier sensing, and utilizes the redundant empty time slots to transmit sleep commands to the tags collected, resulting in performance improvement for tag collection. The simulation results show that the proposed tag collection algorithm can 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.

An effective design of an active RFID reader using a cache of tag memory data

RFID (Radio Frequency Identification) is technology that a reader automatically identifies the data in a tag with a built-in microchip via a radio frequency. The relevant standards for 433 MHz active RFID are ISO/IEC 15961, 15962, and 18000-7. Communication between a reader and a tag in the management of active RFID tag memory data as defined by the standards is not efficient. In this paper, to address efficiency concerns, we present an active RFID reader software design to improve time and transmission rating of the ISO/IEC 18000-7 commands using memory data cached within the reader. We also present a method in which cached memory data are validated before use, to address the cache coherence issue when using multiple readers. For the identification method, we designed two models; one adheres to the RF-interface standard and the other modifies some fields of the RF-interface standard. We designed an active RFID reader and analyzed its efficiency through experiments based on the two models. The experimental results show that the performance on processing time and transmission rating of RF-interface improved by average 60% over the noncache design.

Fast and Reliable Tag Estimation in RFID Systems with Collision-Oblivious Reader

Many RFID systems use dynamic slotted ALOHA to identify the label information of the RFID tags. One of the key problems in the RFID system is how to estimate the number of RFID tags up to the desired level of accuracy. In this paper, we present the framework of tag estimation algorithm for the collision-oblivious (CO) reader which can only decide whether the tag response is successful or not. Thus, the CO reader must rely on the success estimator to predict the RFID tag population. We propose two estimation algorithms to predict the number of RFID tags, named the memoryless success estimator (MSE) and the intersection-based success estimator (ISE). The MSE considers only the estimate obtained at the current inventory round, while the ISE finds an appropriate intersection interval of the existing estimates collected at every inventory round. Through the simulation results, we demonstrate that the ISE is a fast, accurate, and controllable estimator whose performance is close to that of the collision/idle estimators.

An Efficient Tag Collision Detection Method for Active RFID Systems

We propose an efficient tag collision detection method using the asynchronous mode of the RF transceiver for active RFID systems. In the proposed method, active RFID tags communicate using the synchronous mode of the RF transceiver to reduce the packet processing overheads and power consumption, but the active RFID reader uses the asynchronous mode for packet reception from the tags to detect the occurrence of tag collisions by analyzing the raw signal pulses demodulated from the RF transceiver. We implemented an active RFID reader and multiple tags that supported the proposed tag collision detection method. Experiments with a reader and 60 tags showed that the proposed method could detect tag collisions with a high average accuracy of 97.22%, and could choose the optimum frame size dynamically by estimating the number of tags, which results in the improvement of the tag collection performance.

Utilizing Channel Bonding-based M-n and Interval Cache on a Distributed VOD Server

This paper presents a PC cluster-based distributed video on demand (VOD) server that minimizes the load of the interconnection network by adopting channel bonding-based MVIA and the interval cache algorithm Video data is distributed to the disks of each server node of the distributed VOD server and each server node receives the data through the interconnection network and sends it to clients. The load of the interconnection network increases because of the large volume of video data transferred. We adopt two techniques to reduce the load of the interconnection network. First, an Msupporting channel bonding technique is adopted for the interconnection network. n which is a user-level communication protocol that reduces the overhead of the TCP/IP protocol in cluster systems, minimizes the time spent in communicating. We increase the bandwidth of the interconnection network using the channel bonding technique with MThe channel bonding technique expands the bandwidth by sending data concurrently through multiple network cards. Second, the interval cache reduces traffic on the interconnection network by caching the video data transferred from the remote disks in main memory Experiments using the distributed VOD server of this paper showed a maximum performance improvement of compared with a distributed VOD server without channel bonding-based MVIA and the interval cache, when used with a four-node PC cluster.