• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.3
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• pp.181-188
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• 2011

With the rapid proliferation of wireless networks and mobile computing applications, the landscape of the network security has greatly changed recently. Especially, Vehicular Ad Hoc Networks maintaining network topology with vehicle nodes of high mobility are self-organizing Peer-to-Peer networks that typically have short-lasting and unstable communication links. VANETs are formed with neither fixed infrastructure, centralized administration, nor dedicated routing equipment, and vehicle nodes are moving, joining and leaving the network with very high speed over time. So, VANET-security is very vulnerable for the intrusion of malicious and misbehaving nodes in the network, since VANETs are mostly open networks, allowing everyone connection without centralized control. In this paper, we propose a weighted intrusion detection method using rough set that can identify malicious behavior of vehicle node's activity and detect intrusions efficiently in VANETs. The performance of the proposed scheme is evaluated by a simulation study in terms of intrusion detection rate and false alarm rate for the threshold of deviation number ${\epsilon}$.

• Journal of the Korean Applied Science and Technology
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• v.33 no.3
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• pp.483-491
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• 2016

Even though the antifogging property of nanosilica coated glass surface is highly increased due to the hydrophilic hydroxyl groups on nanosilica surface, the durability of this property on outdoor glass was diminished rapidly after rain washing. In addition the topology of nanosilica coated glass surface plays very important roles to control an light transmittance or antireflection property. To improve these coating durability and characteristics a hydrophilic nanosilica coating on glass was prepared by coating with 1.5 wt% of nanosilica (Ludox) suspension in the presence of hydrolyzed tetraethylorthosilicate (TEOS). The optimum hydrolysis condition of TEOS in acidic or basic aqueous solution was also examined by contact angle measurement. The final transparent hydrophilic coating layer coated with nanosilica-TEOS in acidic condition (pH=4) showed much improved durability of hydrophilic surface as well as higher visible light transmittance than original uncoated glass by 2 % point.

• Journal of Communications and Networks
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• v.17 no.1
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• pp.58-66
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• 2015

Aeronautical communication networks (ACN) is an emerging concept in which aeronautical stations (AS) are considered as a part of multi-tier network for the future wireless communication system. An AS could be a commercial plane, helicopter, or any other low orbit station, i.e., Unmanned air vehicle, high altitude platform. The goal of ACN is to provide high throughput and cost effective communication network for aeronautical applications (i.e., Air traffic control (ATC), air traffic management (ATM) communications, and commercial in-flight Internet activities), and terrestrial networks by using aeronautical platforms as a backbone. In this paper, we investigate the issues about connectivity, throughput, and delay in ACN. First, topology of ACN is presented as a simple mobile ad hoc network and connectivity analysis is provided. Then, by using information obtained from connectivity analysis, we investigate two communication models, i.e., single-hop and two-hop, in which each source AS is communicating with its destination AS with or without the help of intermediate relay AS, respectively. In our throughput analysis, we use the method of finding the maximum number of concurrent successful transmissions to derive ACN throughput upper bounds for the two communication models. We conclude that the two-hop model achieves greater throughput scaling than the single-hop model for ACN and multi-hop models cannot achieve better throughput scaling than two-hop model. Furthermore, since delay issue is more salient in two-hop communication, we characterize the delay performance and derive the closed-form average end-to-end delay for the two-hop model. Finally, computer simulations are performed and it is shown that ACN is robust in terms of throughput and delay performances.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.38 no.6
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• pp.1-10
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• 2001

In this paper, we propose a synchronous reservation protocol that is efficient for supporting variable sized messages in a wavelength division multiplexing (WDM) based local network using a passive star topology. A. control channel is used to coordinate transmission on data channels. Time is slotted with fixed-sized slots. The network can accommodate a variable number of nodes, and can operate independently of the change of the number of nodes. So, any 'new' node can join the network anytime without network re-initialization. Moreover, with the protocol, we can avoid data channel and destination conflicts. We analyze the performance by using EPA method according to the variation of the end to end propagation delay with respect to one slot time, and validate the results by simulation.

• Journal of the Korean Association of Geographic Information Studies
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• v.14 no.3
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• pp.1-10
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• 2011

This program was developed to operate and manage the massive digital forest cover type map using SDE(spatial database engine) in order to solve the problems of the analogue mapping system, mapping process and managing vast amounts of data. It was established the standardization process by performing the several functions of application related to the spatial DB search, mapping history and progress control, modification and inspection of the topology error, approval and reject of those maps. It can be possible to generate the effective mapping and distribute maps to the public service. It is expected that the results will be able to reduce time-cost.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.1
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• pp.76-82
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• 2017

Since the introduction of electronically controlled engines and electric propulsion ships, the need for an uninterruptible power supply for emergency power supply devices that use batteries has gained importance. The bidirectional converter in such emergency power supply devices is a crucial component. This paper proposes, a topology for an improved DC-DC bidirectional converter that is characterized by a high voltage conversion ratio and low voltage stress of switches. To confirm the performance of the converter, a computer simulation was executed with PSIM software. The conversion ratio of the proposed converter was found to be four times higher than the conventional boost converter in step-up mode and one-fourth that of the conventional buck converter in step-down mode, and the voltage stress of the switches was one-fourth of the high-side voltage. Moreover, the proposed converter was confirmed to be able to distribute equal currents between two interleaved modules without using any extra current-sharing control method because of the charge balance of its blocking capacitors.

• Journal of the Korea Computer Industry Society
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• v.4 no.10
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• pp.611-620
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• 2003

This paper presents improved GUI based analysis tool o( load flow of power system (or contingency. It is effective tool to facilitate the teaching and learning of load flow of power system. This software is the named of PFGUI(Power Flow GUI) that written in TooIBookII of Asymetrix. The PFGUI is friendly for study for power system operation and control because picture provide a better visualizing of relationships between input parameters and effects than a tabula type result. This PFGUI enables topology and the output data of load flow for line outages to be shown on same picture page. Users can input the system data for power flow on the the picture and can easily see the the result diagram of bus voltage, bus power, line flow. It is also observe the effects of different types of variation of tap, shunt capacitor, loads level, line outages. Proposed PFGUI has been studied on the Ward-Hale 6-Bus system.

• Journal of Power Electronics
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• v.4 no.3
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• pp.138-151
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• 2004

In this paper, a constant frequency phase shifting PWM-controlled voltage source full bridge-type series load resonant high-frequency inverter using the $4^{th}$ generation IGBT power modules is presented for innovative consumer electromagnetic induction heating applications, such as a hot water producer, steamer and super heated steamer. The bridge arm side link passive capacitive snubbers in parallel with each power semiconductor device and AC load side linked active edge inductive snubber-assisted series load resonant tank soft switching inverter with a constant frequency phase shifted PWM control scheme is evaluated and discussed on the basis of the simulation and experimental results. It is proved from a practical point of view that the series load resonant and edge resonant hybrid high-frequency inverter topology, what is called, DE class type, including the variable-power variable-frequency regulation function can expand zero voltage soft switching commutation area even under low output power setting ranges, which is more suitable and acceptable for newly developed induction heated dual pack fluid heaters. Furthermore, even the lower output power regulation mode of this high-frequency load resonant tank inverter circuit is verified so that this inverter can achieve ZVS with the aid of the single auxiliary inductor snubber.

• The KIPS Transactions:PartC
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• v.14C no.2
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• pp.163-170
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• 2007

The next generation communication environment consists of various wireless access networks with distinct features that are configured as an overlay topology. In the network environments, the frequency of hand overs should be minimized and the error propagation should be solved in order to provide high-quality multimedia services to mobile users. Therefore, we propose an performance enhancement approach, based on mSCTP, that provides high quality multimedia services to mobile users by ameliorating the error propagation problem. We utilizes the following four functions: 1) the separation of transmission paths according to the types of frames. 2) retransmission strategy to minimize the loss rate of frames, 3) Foced vertical handover execution by utilizing bicasting, 4) using the stability period in order to reduce the effect of the ping pong phenomenon. The simulation results show that the proposed approach provides seamless multimedia service to mobile users by achieving error resilience.

• The KIPS Transactions:PartA
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• v.14A no.5
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• pp.317-326
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• 2007

We propose more enhanced heuristic for the GOSST(Grade of Services Steiner Minimum Tree) problem in this paper. GOSST problem is a variation of Steiner Tree problem and to find a network topology satisfying the G-Condition with minimum network construction cost. GOSST problem is known as one of NP-Hard or NP-Complete problems. In previous our research, we proposed a heuristic employing Direct Steiner Point Locating strategy with Distance Preferring MST building strategy. In this paper, we propose new Steiner point locating strategy, Zigzag Steiner point Locating strategy. Through the results of out experiments, we can assert this strategy is better than our previous works. The Distance Zigzag GOSST method which hires the Distance Preferring MST building strategy and Zigzag Steiner point Locating strategy defrays the least network construction cost and brings 31.5% cost saving by comparison to G-MST, the experimental control and 2.2% enhancement by comparison to the Distance Direct GOSST method, the best GOSST method in our previous research.