• The Journal of the Korea Contents Association
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• v.10 no.2
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• pp.14-24
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• 2010

Because WSNs operate with limited resources of sensor nodes, its life is extended by cluster-based routing methods. In this study, we use data on direction, distance, density and residual energy in order to maximize the energy efficiency of cluster-based routing methods. Through this study, we expect to minimize the frequency of isolated nodes when selecting a new cluster head autonomously using information on the direction of the upper cluster head, and to reduce energy consumption by switching sensor nodes, which are included in both of the new cluster and the previous cluster and thus do not need to update information, into the sleep mode and updating information only for newly included sensor nodes at the setup phase using distance data. Furthermore, we enhance overall network efficiency by implementing secure and energy-efficient communication through key management robust against internal and external attacks in cluster-based routing techniques. This study suggests the modified cluster head selection scheme which uses the conserved energy in the steady-state phase by reducing unnecessary communications of unchanged nodes between selected cluster head and previous cluster head in the setup phase, and thus prolongs the network lifetime and provides secure and equal opportunity for being cluster head.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.7
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• pp.680-687
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• 2008

This paper presents map creation algorithm and initial attitude estimation method for the proposed optical head tracker system. The optical head tracker system consists of the IR stereo cameras and infrared LEDs as features on the helmet. In order for the stereo camera to track the luminous LEDs, it must take in to account the light radiation from the LEDs to determine the position of the center points. The proposed map creation algorithm makes map data about the position of features center points on the helmet frame. Also, initial attitude estimation method is proposed to estimate the initial attitude and position of a pilot head from the camera frame by the use of the feature pattern on the helmet. Therefore, the head motion can be expressed with respect to the body frame of a flight.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.7
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• pp.685-692
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• 2016

A cutting head is an attachment on the front of an excavator that cuts or grinds rocks. Cutting tools, called pick cutters, are arranged on the surface of the cutting head. The exact arrangement and configuration of pick cutters is one of the most important factors in determining grinding efficiency. This study focuses on the problem of automation for pick arrangement design, in order to make the design process more efficient and convenient. Design automation was carried out using RecurDyn/ProcessNet, and it was composed of three parts: 'Drum set', 'Pick load', and 'Pick arrangement' sections. The presented method helps to decrease costs attributed to designing cutting heads and can be used to generate a wide range of attachment mechanisms.

• Journal of Korean Society of Disaster and Security
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• v.13 no.1
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• pp.51-58
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• 2020

This paper analyzes the effect of airflow of ceiling air conditioner on the operation of sprinkler head using a simulation program. The simulation space is 10 m × 7 m × 3 m, and the size of the fire is 0.8 m × 0.8 m × 0.6 m. The cold air flow from the air conditioner is at 25℃ and the wind speed is divided into three cases : 10 ㎧, 8.5 ㎧, and 7.5 ㎧. Simulation results show that all cases had operating delays compared to when the air conditioner was not running, and the sprinkler head did not operate until 10 minutes had elapsed at 10 ㎧ wind speed. These results confirmed that the sprinkler head was delayed in the air conditioning space and the worst result of early evolution failure was observed in strong winds such as 10 ㎧.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.4B
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• pp.258-268
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• 2012

Wireless Sensor Network(WSN) is constituted by low-cost and low-energy, So the most important issue is that the task of the sensor performs successfully by using less energy. In previous WSN, determination of the header and gathering sensor data solution by header give great affection to the performance of network. In this paper, we propose a Hybrid transmission method which considers the direction of data collections. In the proposed hybrid routing method, all of the sensors determine that transmission the data to the sink node directly or indirectly using the head node depend on the location of the head node in the cluster. The performance is compared with the LEACH(Low Energy Adaptive Clustering Hierarchy) by experimental analysis. The results show that the preposed method can reduce the communication distance and energy consumption by avoiding the detour direction of transmission of the data.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.6C
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• pp.632-639
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• 2002

To reduce the area and power consumption in constant coefficient multiplications, the constant coefficient can be encoded using canonic signed digit(CSD) representation. When the partial product terms are added depending on the nonzero bit(1 or -1) positions in the CSD-encoded multiplier, all sign bits are properly extended before the addition takes place. In this paper, to reduce the overhead due to sign extension, a new method is proposed based on the fact that carry propagation in the sign extension part can be controlled such that a desired input bit can be propagated as a carry. Also, a fixed-width multiplier design method suitable for CSD multiplication is proposed. As an application, 43-tap filbert transformer for SSB/BPSK-DS/CDMA is implemented. It is shown that, about 16∼28% adders can be saved by the proposed method compared with the conventional methods.

• Journal of KIISE:Information Networking
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• v.37 no.5
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• pp.327-338
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• 2010

Complete Subtree scheme(CS) is a well known broadcast encryption scheme to perform group rekeying in a stateless manner. However, statelessness comes at a cost in terms of storage and message overhead in transmitting key material. We propose a Merged Complete Subtree scheme(MCS) to reduce the communication overhead. It is more practical to make broadcast encryption schemes in network environments with limited bandwidth resources. We define all possible subset unions for ever two subsets of CS as new subsets having own key. The modification causes more storage overhead. Nevertheless, it is possible to make the size of a header, including key materials, half using subset unions of MCS, because the size of a header depends on the number of used subsets. Our evaluation therefore shows that the proposed scheme significantly improves the communication overhead of CS, reducing by half the rekey communication cost. The proposed scheme has the advantage of rekey communication cost when the number of revoked users is significant percentage of the number of potential users. The proposed scheme is fully collusion resistant.

• Annual Conference of KIPS
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• 2012.11a
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• pp.792-795
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• 2012

애드 혹 네트워크(MANET: Mobile Ad hoc NETworks)는 기본적인 내부구조(infrastructure) 없이 노드들만으로 네트워크 망을 구성한다. 경로 탐색 정책으로 리액티브(reactive) 방식과 프로액티브(proactive) 방식이 있는데, 전통적으로 리액티브 방식의 성능이 더 좋은 것으로 평가된다. 그리고 두가지 방식의 장점을 취합한 하이브리드(hybrid) 방식의 클러스터 토폴로지(cluster topology) 도입에 관한 연구가 이루어지고 있다. 그 중, HCR(Hybrid Cluster Routing)이 제안되었는데, 이는 프로액티브 방식에 보다 중심을 둔 기법이다. HCR 은 리액티브 방식 경로 탐색 방법인 플라딩(flooding)의 탐색 지역을 한정된 범위로 제한할 수 있으나, 프로액티브 방식의 전체 네트워크 구성 정보 유지에 따른 막대한 오버헤드를 발생한다. 본 논문에서는 이러한 오버헤드를 줄이기 위해, 클러스터 내부 경로 탐색 기법인 MICF(Maginot path based Intra Cluster Flooding)를 제안한다. MICF 는 HCR 을 개선한 FSRS(First Search and Reverse Setting) 기반의 기법으로서, 클러스터 내부의 마지노 패스(maginot path)를 기준으로 경로 탐색 지역을 제한한다. MICF 는 게이트웨이(gateway) 간 최단 거리가 항상 클러스터 헤드(cluster head)를 중점으로 원의 내각 지역에 존재함을 바탕으로 하며, 최단 경로의 보장과 플라딩 지역 제한을 동시에 만족한다. 실험 결과, MICF 는 FSRS 기반의 기존 클러스터 내부 플라딩 방식보다 총 에너지의 7.79%만큼 더 에너지를 보존하였다. 결론적으로, MICF 역시 기존의 방식보다 에너지를 더 효율적으로 사용할 수 있으며, 마지노패스 설정과 이를 기반으로 한 제어 과정에 추가적인 오버헤드가 발생하지 않는다. 그리고 플라딩 면적이 작을수록 오버헤드가 줄어들게 됨을 알 수 있다.

• The Journal of Korean Institute of Information Technology
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• v.17 no.11
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• pp.17-26
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• 2019

RAID-5 technology is one of the choice for flash storage device to enhance its reliability. However, RAID-5 has inherent parity update overhead, especially, parity overhead for partial stripe write is one of the crucial issues for flash-based RAID-5 technologies. In this paper, we design efficient parity log architecture for RAID-5 to eliminate runtime partial parity overhead. During runtime, partial parity is retained in buffer memory until full stripe write completed, and the parity is written with full strip write. In addition, parity log is maintained in memory until whole the stripe group is used for data write. With this parity log, partial parity can be recovered from the power loss. In the experiments, the parity log method can eliminate partial parity writes overhead with a little parity log writes. Hence it can reduce write amplification at the same reliability.

• Journal of the Korean Society of Propulsion Engineers
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• v.26 no.3
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• pp.54-65
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• 2022

We are developing a compact ignition device that can provide a multi-ignition capability for an upper stage methane engine of a two staged small satellite launch vehicle. Firstly, the multi-ignition device is designed and built as an integral part of an additively manufactured mixing head. Secondly, the ignition device requires no separate high-pressure vessels to store ignition propellants as they are branched out from the main feed lines for the mixing head. We performed experiments at various levels, including igniter autonomous tests, thrust chamber ignition and combustion tests on the new compact ignition device which is integrated in the thrust chamber of one-tonf class liquid oxygen/liquid methane engine, and confirmed stable ignition performance.