Sang-Hwa Chung

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.

A Node-Disjoint Multipath Routing Protocol Based on AODV in Mobile Ad Hoc Networks

In this paper, we propose a new multi-path routing protocol in MANET that is composed of high-mobility nodes. The new multi-path routing establishes the main route by the mechanism based on AODV, and then the data transmission starts immediately. The backup route search process is taking place while data is transmitted to reduce the transmission delay. This process finds the route that is node-disjoint from the main route by not selecting nodes participate in the main route. When either of the main route or the backup route is broken, data is transmitted continuously through the other route and the broken route is recovered by the route maintenance process. The result of the simulation based on the Qualnet simulator shows that proposed routing protocol has the backup route 62.5% of the time when the main route is broken, improves the packet transmission rate by 2~3% and reduces the end-to-end delay by 10% compared with AODV and AODV-Local Repair

ISS-TCA: An Identified Slot Scan-Based Tag Collection Algorithm for Performance Improvement in Active RFID Systems

The standard tag collection algorithm (TCA) in ISO/IEC 18000-7 has difficulty in collecting data from a massive number of active radio frequency identification (RFID) tags in a timely manner, so it should be improved to allow successful application of active RFID systems to a wide variety of industrial fields. We propose a novel TCA, which is an identified slot scan-based TCA (ISS-TCA), to improve the performance of tag collection (TC) in active RFID systems. In the proposed ISS-TCA, an active RFID reader differentiates identified slots from collided and empty slots via an ISS phase, in which active RFID tags send minimal responses. The reader then avoids collided and empty slots in the following TC phase, in which it collects the actual data from the tags. This reduces the cost of collided and empty slots during TC, resulting in improved TC performance. We carried out simulations to evaluate and compare the performances of the standard TCA and the proposed ISS-TCA in TC. The simulation results with up to 500 tags showed that the proposed ISS-TCA reduced the average time required for TC by 33.2% or 27.3% when the reader collected 50 or 100 bytes of additional data from the tags, respectively. We also experimentally evaluated the performance improvement of TC by the proposed ISS-TCA using an active RFID reader and 60 tags that were implemented for this paper. The experimental results confirmed that the proposed ISS-TCA could improve the TC performance in practice, confirming the simulation results, and showed that it could also decrease the average battery consumption of the tags by 39.3%.

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.

Estimating Rate of Queue Usage to Differentiate Cause of Packet Loss in Multi-hop Wireless Networks

When TCP operates in multi-hop wireless networks, it suffers from severe performance degradation. This is because TCP considers all packet losses as congestion signals, and reacts even to wireless packet losses by decreasing unnecessarily its sending rate. Although several loss differentiation schemes are proposed to avoid such performance degradation, these schemes are designed for the last-hop wireless networks, and their accuracies in wireless loss discrimination are not high as much as we expect. In this paper, we suggest a new end-to-end loss differentiation which works entirely at the TCP sender. To improve its accuracy, we estimate the rate of queue usage using information available to TCP. If the estimated queue usage is larger than a certain threshold when a packet is lost, our scheme diagnoses the packet loss as congestion losses. Otherwise it assumes the packet loss as wireless losses. Through the extensive simulations, we compare and evaluate our scheme with previous schemes in terms of accuracy and stability. And the results show that our scheme has the highest accuracy among the previous schemes, and its accuracy is reliable under various multi-hop wireless network conditions.

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.

A Timestamp based Detection of fast retransmission loss for improving the performance of TCP NewReno over wireless networks

NewReno is the most widely deployed TCP protocol in todays internet. When NewReno operates in wireless networks, the performance of NewReno degrades significantly. Frequent retransmission timeout is one of the well-know problems of the performance degradation of TCP NewReno over wireless networks. In wireless networks, a retransmission timeout is unavoidable, when the fast retransmission of a lost packet fails to reach the destination particularly due to the changing level of congestion and bit error rate in wireless channel. There have been many schemes developed for reducing the retransmission timeouts. However, these schemes have no mechanism to detect the loss of fast retransmitted packets. In this paper, we introduce an efficient mechanism based on TCP NewReno, called T-DLRP (Timestamp based- Detection of the Loss of fast Retransmitted Packets) which is able to detect fast retransmission loss and react accordingly without waiting for retransmission timeouts even multiple loss of packets in a single window of data and the loss of its fast retransmission. T-DLRP consists of three schemes, called FRL (Fast Retransmission Loss)-Detection, FRL-Differentiation and Immediate fast recovery. Through extensive simulations using qualnet 4.5, we evaluate the performance of TDRLP and demonstrate that our mechanism achieves 40–90% performance improvement than key existing TCP schemes over wireless networks especially when the network co-existed with packet loss and retransmission losses.