• Proceedings of the Korea Society for Simulation Conference
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• 2005.11a
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• pp.108-112
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• 2005

유비쿼터스 컴퓨팅의 기반 설비인 센서 네트워크는 많은 수의 센서 노드들로 구성되며, 각 센서 노드의 하드웨어는 매우 작은 규모이다. 또한 센서 네트워크는 구축 목적에 따라 네트워크 토폴로지 및 라우팅 방식이 결정되어야 하고, 이와 더불어 센서 노드의 하드웨어와 소프트웨어도 필요에 따라 다양하게 변경되어야 한다. 따라서 센서 네트워크가 구현되기 전에 시스템 동작과 성능을 예측할 수 있는 센서 네트워크 시뮬레이터가 필요하다. 기존의 센서 네트워크 시뮬레이터들은 특별한 응용을 위한 특정 기반의 하드웨어와 운영체제에 국한되어 개발되었기 때문에 다양한 센서 네트워크 환경을 지원하기에는 한계가 있으며, 센서 네트워크 설계상의 주요 요소인 전력소모량과 실행 시간에 대한 분석이 포함되지 않았다. 따라서 본 연구에서는 특정한 응용이나 운영체제에 제한을 받지 않으면서 다양하게 센서 네트워크 환경을 설계 및 검증할 수 있고, 더불어 전력소모량과 실행시간 추정도 가능한 시뮬레이터를 개발하는 것을 목표로 하였다. 이를 위해 본 연구에서 개발한 시뮬레이터는 기계명령어-레벨(machine instruction-level)의 이산-사건 시뮬레이션(discrete-event simulation) 기법을 이용함으로써 실제 센서 노드의 프로그램 실행 및 관련 동작들을 세부적으로 예측하는 데 사용될 수 있도록 하였다. 시뮬레이션의 작업부하(workload)인 명령어 트레이스(instruction trace)로는 ATmega128L 마이크로컨트롤러용으로 크로스 컴파일된 인텔 핵스-레코드(.hex) 형식을 사용한다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.10a
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• pp.571-573
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• 2009

Mobile Ad-hoc Network(MANET) needs efficient node management because the wireless network has energy constraints. Mobility of MANET would require the topology change frequently compared with a static network. To improve the routing protocol in MANET, energy efficient routing protocol would be required as well as considering the mobility would be needed. Previously proposed a hybrid routing CACH prolong the network lifetime and decrease latency. However the algorithm has a problem when node density is increase. In this paper, we propose a new method that the CACHE(Context-aware Clustering Hierarchy and Energy efficient) algorithm. The proposed analysis could not only help in defining the optimum depth of hierarchy architecture CACH utilize, but also improve the problem about node density.

• Proceedings of the KIPE Conference
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• 2019.07a
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• pp.92-94
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• 2019

양방향 스위치를 가지는 Bridgeless PFC 컨버터(BBPFC)는 구조상 복잡한 플로팅 게이트 드라이버를 활용함에도 불구하고 좋은 공통모드 잡음 즉, Common-Mode (CM) 노이즈 특성과 간단한 제어 방법으로 인해 많은 브리지리스 PFC 컨버터 중에서도 고전력 응용분야에서 매우 매력적인 토폴로지이다. 이러한 BBPFC는 도통 경로 상에 위치한 정류 다이오드의 역회복 특성의 상대적인 편차를 활용하여 전력 밀도를 감소시키지 않고도 좋은 공통모드 (CM) 노이즈 특성의 확보가 가능하다. 하지만 이러한 장점을 가지는 BBPFC 구조를 고전력 서버용 전원장치분야에서 활용할 경우, 이미 등록된 특허로 인해 매우 높은 개런티를 지불해야 하므로 그 활용이 매우 제한적이다. 따라서, 본 논문에서는 이미 등록된 특허를 회피하고, 동시에 기존 BBPFC 회로가 가지는 단점인 플로팅 게이트 드라이버를 활용하는 단점을 개선하는 새로운 형태의 브리지리스 PFC 컨버터를 제안한다. 제안된 컨버터는 기존 BBPFC가 가지는 장점인 좋은 (CM) 노이즈 특성을 가지며, 동시에 높은 효율을 달성 할 수 있다. 또한 제안된 컨버터의 경우, 복잡한 플로팅 형태의 게이트 드라이버 회로가 아닌 간단한 부트스트랩 회로를 활용하여 회로를 운용할 수 있다. 더불어 제안된 컨버터는 입력의 양과 음의 주기에서 단 하나의 스위치를 사용하여 회로를 구동할 수 있기 때문에 기존회로 대비 적은 손실을 가져 높은 효율의 획득이 가능하다. 본 논문에서는 제안된 구조에 대해 하이라인 $230V_{RMS}$ 입력과 800W / 400V 출력의 조건을 적용하여 제안하는 구조의 효용성을 검증하고자 한다.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.36C no.11
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• pp.64-74
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• 1999

A new clock skew optimization for clock routing using link-edge insertion is proposed in this paper. It satisfies the given skew bound and prevent the total wire length from increasing. As the clock skew is the major constraint for high speed synchronous ICs, it must be minimized in order to obtain high performance. But clock skew minimization can increase total wire length, therefore clock routing is performed within the given skew bound which can not induce the malfunction. Clock routing under the specified skew bound can decrease total wire length Not only total wire length and delay time minimization algorithm using merging point relocation method but also clock skew reduction algorithm using link-edge insertion technique between two nodes whose delay difference is large is proposed. The proposed algorithm construct a new clock routing topology which is generalized graph model while previous methods uses only tree-structured routing topology. A new cost function is designed in order to select two nodes which constitute link-edge. Using this cost function, delay difference or clock skew is reduced by connecting two nodes whose delay difference is large and distance difference is short. Furthermore, routing topology construction and wire sizing algorithm is developed to reduce clock delay. The proposed algorithm is implemented in C programming language. From the experimental results, we can get the delay reduction under the given skew bound.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.3
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• pp.281-285
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• 2008

Wireless sensor networks are closely related with the geometric environment in which they are deployed. We consider the probable case when a routing protocol runs on an environment with many complex obstacles like downtown surroundings. In addition, there are no unrealistic assumptions in order to increase practicality of the protocol. Our goal is to find a routing protocol for maximizing network lifetime by using only connectivity information in the complex sensor network environment. We propose a topology-based routing algorithm that accomplishes good performance in terms of network lifetime and routing complexity as measures. Our routing algorithm makes routing decision based on a weighted graph as topological abstraction of the complex network. The graph conduces to lifetime enhancement by giving alternative paths, distributing the skewed burden. An energy estimation method is used so as to maintain routing information without any additional cost. We show how our approach can be used to maximize network lifetime and by extensive simulation we prove that out approach gives good results in terms of both measures-network lifetime and routing complexity.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.4
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• pp.195-200
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• 2020

With the growing interest in fossil fuel depletion and environmental pollution, railroad cars operating in Korea are in progress as the conversion from diesel to electric vehicles expands. The photovoltaic system, which is applied as an example of the conversion of electric vehicles, is infinite and pollution-free, and can produce energy without generating hazards such as air pollution, noise, heat, and vibration, and maintain fuel transportation and power generation facilities. There is an advantage that is rarely needed. However, the amount of electricity produced depends on the amount of solar radiation by region, and the energy density is low due to the power generation of about 25㎡/ kWp, so a large installation area is required and the installation place has limited problems. In view of these problems, many studies have been applied to fuel cells in the railway field. In particular, the plan to link the fuel cell power generation system railroad power supply system must be linked to the power supply system that supplies power to the railroad, unlike solar and wind power. Therefore, it has a close relationship with railroad cars and the linkage method can vary greatly depending on the system topology. Therefore, in this paper, we study the validity through simulation modeling related to linkage analysis according to system topology.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.7 no.6
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• pp.92-100
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• 2008

Ad-hoc network is a collection of wireless mobile hosts forming a temporary network without the aid of any centralized administration or reliable support services such as wired network and base stations. Recently, Ad-hoc networks are evolving to support multimedia contents according to expansion of ad hoc multi-hop communication system. Wireless ad-hoc network is different from the conventional wired network by frequent changes in network topology, number of routers and resources, there are a number of problems in applying conventional routing protocol to ad-hoc network. The AODV routing protocol is proposed for mobile node in ad-hoc networks. AODV protocol that provides to guarantee QoS for data transmission in ad hoc networks that link break frequently occurs. In this paper, AODV routing protocol based NDIS(Network Driver Interface Specification) is implemented. We design high performance image transmission that can operate with software(AODV) for ad-hoc networks without degradation. and verify operation of AODV routing protocol on the test bed.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.48 no.2
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• pp.86-95
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• 2011

Sensor nodes in wireless sensor networks are vulnerable to security than wired network due to using limited hardware performance and wireless communications that network topology changes frequently. Among techniques to enhance the security, the node authentication mechanism is used to defend against data forgery attacks using the ID of the node or to interfere with the routing of the network routing. In this paper, we proposed the AM-E mechanism that makes authentication key by using the energy value of node requesting authentication and performs the communication procedures for data transfer between different nodes. Because the energy value of node is changed depending on time, every time the authentication request is, an authentication key is changed. These features enhance the security of sensor networks and will help to configure the more secure WSN.

• Journal of the Korea Society of Computer and Information
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• v.25 no.9
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• pp.81-90
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• 2020

In order to operate multi drone efficiently, existing control methods must be improved, and drones must be able to construct communication networks autonomously. FANET(Flying Ad-Hoc Network), which is being considered as an alternative to solving these problems, is based on ad hoc network technology and can be exposed to a variety of security vulnerabilities. However, due to the limited computational power and memory of FANET nodes, and rapid and frequent changes in network topology, it is not easy to apply the existing security measures to FANET without modification. Thus, this paper proposes lightweight security measures applicable to FANET, which have distinct characteristics from existing ad hoc networks by utilizing PUF technology. The proposed security measures utilize unique values generated by non-replicable PUFs to increase the safety of AODV, FANET's reactive routing protocol, and are resistant to various attacks.

• KIPS Transactions on Software and Data Engineering
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• v.4 no.9
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• pp.385-392
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• 2015

In IoT(Internet of Things), it is important for wireless networks to communicate data created among resource-constrained wireless nodes, where time synchronization is needed for meaningful data creation and transmission. Time Synchronization by flooding is one of the mostly used protocols for WSN(Wireless Sensor Networks). Even though this type of scheme has some advantages over other types (i.e. a simple algorithm and independency of topology and so on), too many data transmission is required, leading to large power consumption. So, reducing transmission data is an important issue for energy efficiency in this kind of networks. In this paper, a new Flooding-based time synchronization protocol is proposed to use energy efficiently by reducing a transmitted traffic. The proposed scheme's performance has been evaluated and compared with an representative scheme, FTSP(Flooding Time Synchronization Protocol) by simulation. The results are shown that the proposed scheme is better than FTSP.