• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2007.05a
• /
• pp.448-452
• /
• 2007

Many industrial operations require continuous or nearly-continuous operation of machines, which if interrupted can result in significant financial loss. The condition monitoring of these machines has received considerable attention recent years. Rapid developments in semiconductor, computing, and communication with a remote site have led to a new generation of sensor called "smart" sensors which are capable of wireless communication with a remote site. The purpose of this research is the development of smart sensor using which can on-line perform condition monitoring. This system is addressed to detect conditions that may lead to equipment failure when it is running. Moreover it will reduce condition monitoring expense using low cost MEMS accelerometer. This sensor can receive data in real-time or periodic time from MEMS accelerometer. Furthermore, this system is capable for signal preprocessing task (High Pass Filter, Low Pass Filter and Gain Amplifier) and analog to digital converter (A/D) which is controlled by CPU. A/D converter that converts 10bit digital data is used. This sensor communicates with a remote site PC using TCP/IP protocols. Wireless LAN contain IEEE 802.11i-PSK or WPA (PSK, TKIP) encryption. Developed sensor executes performance tests for data acquisition accuracy estimations.

• Journal of Electrical Engineering and Technology
• /
• v.9 no.6
• /
• pp.2019-2024
• /
• 2014

This paper presents a method to optimize the design of a planar-type antenna and reduce the number of design parameters for rapid computation. The electromagnetic characteristics of the structure are analyzed, and Taguchi method is used to identify critical design parameters. Adaptive particle swarm optimization, which has a faster convergence rate than particle swarm optimization, is used to achieve the design goal effectively. A compact dual-band USB dongle antenna is tested to verify the advantage of the proposed method. In this case, we can use only five selected geometrical parameters instead of eighteen to accelerate the optimization of the antenna design. The 10 dB bandwidth for return loss ranges from 2.3 GHz to 2.7 GHz and from 5.1 GHz to 5.9 GHz, covering all the WiBro, Bluetooth, WiMAX, and 802.11 b/g/n WLAN bands in both simulation and measurement. The optimization process enables the antenna design to achieve the required performance with fewer design parameters.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.8 no.10
• /
• pp.3458-3474
• /
• 2014

The performance of IEEE 802.11e enhanced distributed channel access (EDCA) is influenced by several interactive parameters that make quality of service (QoS) control complex and difficult. In EDCA, the most critical performance influencing parameters are the arbitration interframe space (AIFS) and contention window size (CW) of each access category (AC). The objective of this paper is to provide a scheme for parameter control such that the throughput per station as well as the overall system throughput of the network is maximized and controllable. For this purpose, a simple and accurate analytical model describing the throughput behavior of EDCA networks is presented in this paper. Based on this model, the paper further provides a scheme in which a Pareto optimal system configuration is obtained via an appropriate CW control for a given AIFS value, which is a different approach compared to relevant papers in the literature that deal with CW control only. The simulation results confirm the effectiveness of the proposed method which shows significant performance improvements compared to other existing algorithms.

• Journal of KIISE:Software and Applications
• /
• v.29 no.11
• /
• pp.795-802
• /
• 2002

We propose a fast and powerful Question-answering (QA) system in Korean, which uses a predictive answer indexer based on 2-pass scoring method. The indexing process is as follows. The predictive answer indexer first extracts all answer candidates in a document. Then, using 2-pass scoring method, it gives scores to the adjacent content words that are closely related with each answer candidate. Next, it stores the weighted content words with each candidate into a database. Using this technique, along with a complementary analysis of questions which is based on lexico-syntactic pattern matching method, the proposed QA system saves response time and enhances the precision.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.3 no.4
• /
• pp.399-422
• /
• 2009

Although current wireless mesh network (WMN) applications experience a perceptually uninterrupted hand-off, their throughput after the hand-off event may be significantly degraded due to the low available bandwidth of the mobile client's new master. In this paper, we propose a novel mobility management scheme for 802.11-based WMNs that enables both seamless hand-off for transparent communications, and bandwidth awareness for stable application performance after the hand-off process. To facilitate this, we (i) present a new buffer moment in support of the fast Layer-2 hand-off mechanism to cut the packet loss incurred in the hand-off process to zero and (ii) design a dynamic admission control to grant joining accepts to mesh clients. We evaluate the benefits and drawbacks of the proposal for both UDP and TCP traffic, as well as the fairness of the proposal. Our results show that the new scheme can not only minimize hand-off latency, but also maintain the current application rates of roaming users by choosing an appropriate new master for joining.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.19 no.1
• /
• pp.121-131
• /
• 2020

Current traffic information is collected through a loop detector or an image detector. This method is influenced by weather and time, so a traffic information generation system is needed to replace it. A system for generating traffic information using a smartphone in a vehicle is proposed and the performance of the proposed method is verified through the collection rate and the travel time error rate obtained through field tests. In addition, we propose an algorithm for generating intersection traffic information for each direction of rotation, suggest ways to increase the amount of valid information, and confirm the results.

• Journal of Communications and Networks
• /
• v.11 no.6
• /
• pp.615-625
• /
• 2009

Worldwide inter-operability for microwave access (WiMAX) is a promising technology that provides high data throughput with low delays for various user types and modes of operation. While much research had been conducted on physical and MAC layers, little attention has been paid to a comprehensive and efficient security solution for WiMAX. We propose a hybrid security solution combining identity-based cryptography (IBC) and certificate based approaches. We provide detailed message exchange steps in order to achieve a complete security that addresses the various kind of threats identified in previous research. While attaining this goal, efficient fusion of both techniques resulted in a 53% bandwidth improvement compared to the standard's approach, PKMv2. Also, in this hybrid approach, we have clarified the key revocation procedures and key lifetimes. Consequently, to the best of knowledge our approach is the first work that unites the advantages of both techniques for improved security while maintaining the low overhead forWiMAX.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.13 no.3
• /
• pp.1123-1140
• /
• 2019

Many Internet of Things (IoT) applications involving bursty traffic have emerged recently with event detection. A power management scheme qualified for uplink bursty traffic (PM-UBT) is proposed by distinguishing between bursty and general uplink traffic patterns in the IEEE 802.11 standard to balance energy consumption and uplink latency, especially for stations with limited power and constrained buffer size. The proposed PM-UBT allows a station to transmit an uplink bursty frame immediately regardless of the state. Only when the sleep timer expires can the station send uplink general traffic and receive all downlink frames from the access point. The optimization problem (OP) for PM-UBT is power consumption minimization under a constrained buffer size at the station. This OP can be solved effectively by the bisection method, which demonstrates a performance similar to that of exhaustive search but with less computational complexity. Simulation results show that when the frame arrival rate in a station is between 5 and 100 frame/second, PM-UBT can save approximately 5 mW to 30 mW of power compared with an existing power management scheme. Therefore, the proposed power management strategy can be used efficiently for delay-intolerant uplink traffic in event-driven IoT applications, such as health status monitoring and environmental surveillance.

• Journal of Environmental Science International
• /
• v.28 no.11
• /
• pp.917-925
• /
• 2019

All of the animals and the plants in ecosystem are intimately connected to one another and the changes of forests and surroundings affect directly wild animals. This study was conducted at Hangyeong-myeon Cheongsu-ri located in the western part of Jeju Island belonging to Hangyeong Andeok Gotjawal Zone and Jocheon-eup Seonheul-ri located in the eastern part of Jeju Island belonging to Jocheon Hamdeok Gotjawal Zone. The survey on advent of birds was carried out twice a month from January 2014 to December 2015. We divided habitat environments into three survey sites such as a forest, a shrub forest and a farmland. A total of 65 species and 4,802 individuals were observed during the survey period. In a forest, 36 species and 1,287 individuals were observed while A shrub forest had 40 species and 1,554 individuals. And in a farmland, 41 species and 1,961 individuals were observed. The only 10 species were observed in forest and the only 7 species in shrub forest and the only 10 species in farmland. The species diversity and the evenness of a farmland were the highest, and the species richness was the highest in a shrub forest, and the dominance of a forest was the highest among the three areas. The similarity index between a shurb forest and a farmland was high while that between a forest and a farmland was low. The similarity index related with breeding appeared that a forest and a farmland was different from each other.

• ETRI Journal
• /
• v.38 no.4
• /
• pp.634-644
• /
• 2016

Channel-based radio-frequency fingerprinting such as a channel impulse response (CIR), channel transfer function (CTF), and frequency coherence function (FCF) have been recently proposed to improve the accuracy at the physical layer; however, their empirical performance, advantages, and limitations have not been well reported. This paper provides a comprehensive empirical performance evaluation of RF location fingerprinting, focusing on a comparison of received-signal strength, CIR-, CTF-, and FCF-based fingerprinting using the weighted k-nearest neighbor pattern recognition technique. Frequency domain channel measurements in the IEEE 802.11 band taken on a university campus were used to evaluate the accuracy of the fingerprinting types and their robustness to human-induced motion perturbations of the channel. The localization performance was analyzed, and the results are described using the spatial and temporal radio propagation characteristics. In particular, we introduce the coherence region to explain the spatial properties and investigate the impact of the Doppler spread in time-varying channels on the time coherence of RF fingerprint structures.