• Journal of Internet Computing and Services
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• v.9 no.4
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• pp.21-27
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• 2008

TCP receivers deliver ACK packets to senders for reliable end-to-end transfer. When ACK packets are not transferred properly because of network congestion, the performance of TCP degrades. This paper proposes a reverse congestion warning mechanism and a congestion handling mechanism in heterogeneous networks with heavy background traffic in the backward direction. Help from TCP receivers or hardware such as routers and gateways other than the ACK packets themselves is not necessary. TCP senders compare the arrival intervals of ACK data passed from receivers and the difference in t imestamp values echoed by receivers. According to the simulation results using the NS-2 network simulator, the proposed scheme shows a performance elevation of 20% greater than Reno, 150% greater than New Reno, and 450% greater than Westwood, respectively, under heterogeneous networks and that the error rate of the radio link is 1% when the backward network is congested.

• Journal of KIISE:Computing Practices and Letters
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• v.9 no.6
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• pp.674-682
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• 2003

Ship autonomous navigation is designated as what computerizes mental faculties possessed of navigation experts, which are building navigation plans, grasping the situation, forecasting the fluctuation, and coping with the situation. An autonomous navigation system, which consists of several subsystems such as navigation system, a collision avoidance system, several data fusion systems, and a motion control system, is based on an intelligent control architecture for the sake of integrating the systems. The motion control system, which is one of the most essential system in autonomous navigation system, controls its propulsion and steering gears to move the ship satisfying its hydrodynamic characteristics. This paper is the study on the ship movement control system and its implementation which are totally developed and run on virtual-world system. Receiving the high-level control values such as a waypoint presented from the collision avoidance system, the motion control system generates them to low-level control values for propulsion and steering devices. In the paper, we develop a ship motion controller using Oldenburger's theory based on mathematical fundamentals, and simulate it with various scenarios in order to verify its performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.4C
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• pp.371-379
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• 2002

In this paper, the MMIC SPST switches operating from DC to 3GHz were designed and implemented. Prior to the design of switches, the small and large-signal switch models were needed to predict switch performance accurately. The newly proposed small-signal switch model parameters were extracted from measured S-parameters using optimization technique with estimated initial values and boundary limits. In the extraction of large-signal switch model parameters, the current source was modeled by fitting empirical equations to measured DC data and the charge model was derived from extracted channel capacitances from measured S-parameters varying the drain-source voltage. To design basic series-shunt SPST switches and isolation-improved SPST switches, we applied this model to commercial microwave circuit simulator. The improved SPST switches exhibited 0.302dB insertion loss, 35.762dB isolation, 1.249 input VSWR, 1.254 output VSWR, and about 15.7dBm PldB with 0/-3V control voltages at 3GHz.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.8A
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• pp.858-870
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• 2007

TCP is popular protocol for reliable data delivery in the Internet. In recent years, wireless environments with transmission errors are becoming more common. Therefore, there is significant interest in using TCP over wireless links. Previous works have shown that, unless the protocol is modified, TCP may perform poorly on paths that include a wireless link subject to transmission errors. The reason for this is the implicit assumption in TCP that all packet losses are due to congestion which causes unnecessary reduction of transmission rate when the cause of packet losses are wireless transmission errors. In this paper, we propose a new LDA that monitors the network congestion level using ROTT. And we evaluate the performance of our scheme and compare with TCP Veno, Spike scheme with NS2(Network Simulator 2). In the result of our experiment, our scheme reduces the packet loss misclassification to maximum 55% of other schemes. And the results of another simulation show that our scheme raise its transmission rate with the fairness preserved.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.10B
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• pp.865-875
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• 2008

In this paper, we propose a reliable multicast scheme for the tactical wireless ad hoc network where the members share the situation and operation data. Our scheme consists of two phases to guarantee the reliability. During the dissemination phase, we utilizes an epidemic approach similar to gossip-based ad hoc routing. Then the group members interchange the message reception state information periodically so that they are able to recover missing packets from the other members. We evaluate the performance of our scheme through extensive simulations using the network simulator in comparison with other existing reliable multicast schemes in mobile ad hoc network. Our scheme shows higher packet delivery ratio regardless of the mobility and imposes much lower control overhead to the non-group members compared with the existing schemes.

• Journal of the Korea Society of Computer and Information
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• v.13 no.6
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• pp.253-261
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• 2008

Mobile games will be one of independent industries on game areas and take the fourth standing in the important platform since PC Games, TV Games, and Palm Games. There are several reasons why mobile games will differ in their platform, behaviors, and habits. According to the data of market consultation about the figure of mobile-game players throughout the world, the Mobile game will increase steadily from 780 million in 2007 to 1860 million in 2010. Also, market income will mount up from $42,100 million to $87,000 million. 3D games have been playing important roles in our lives. Satisfying users' needs in high-quality games, they have been growing and attracting more people with their powerful visual effects and the three-dimensional design player. We cannot emphasize their tremendous visual impacts and animation effects too much. This paper displays how to design 3D application based on J2ME (Java 2 Micro Edition) and shows free movement of 3D objects receiving and responding to the keyboard of mobile devices withWTK (Wireless ToolKit) simulator on the 3D screen.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.2101-2108
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• 2008

Most of train fires which occur in usual cases do not grow up significantly on a large scale enough to bring about casualties and harmful damages. However, the consequence of some train fire accidents can be devastating disaster so that it would be even recorded in history in unusual cases. Accordingly, such a probability of fire disaster cannot be ignored in aspect of the railway safety assesment. A scale of injury and damage is very difficult to predict and analyze. Because it is depend on various factors, i.e. fire load, burning period, facilities, environment condition, and so on. Thus, a prediction of fire load could be understood as a one methodology to estimate railway safety assesment. The summation method which is one of them is used to evaluate the overall fire load by assuming that sum of heat release rate per unit area or mass of each composite material equals the total. However, since the train fire is classified into a compartment fire in under-ventilation condition. The summation method do not estimate a fire load completely. In this journal, Various methods to predict fire load are introduced and evaluated. Especially the fire simulation tool FDS(Fire Dynamics Simulator)which is based on the CFD(Computational Fluid Dynamics) is introduced, too. Through the FDS simulation, numerical analyses for the fire load and flame spread are performed. Then, these results of the simulation are validated through the comparison study with the experimental data. Then, limitations and approximations including in simulation process are discussed. The future direction of research is proposed.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.8
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• pp.33-44
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• 2000

The lightning with high voltage and current can enter the basestations for mobile communication through their antenna. The device which can protect the basestation against the lightning, is surge arrestor. In this paper, the concept, kind, operating mechanism, design and fabrication of surge arrestor were studied. Based on the studied data, variable surge arrestors were designed for the current mobile communication service like a cellular, GSM and PCS and the next generation mobile communication like a IMT-2000. Computer simulation for the prediction of their characteristics and inner structure optimization for the improvement of their electrical characteristics were carried with high frequency 3D structure simulator. Quarter wave short stub surge arrestors for IMT-2000 were fabricated with their final design and then the measurement of electrical characteristics and the lightning test were executed. As a results of measurement, we obtained below 1.05 of VSWR, -0.035 dB of insertion loss, -150 dBc of intermodulation and 7∼ll V of residual voltage.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.1
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• pp.43-50
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• 2016

NAND flash based storage devices adopts multi-channel and multi-way architecture to improve performance using parallel operation of multiple NAND devices. However, multiple NAND devices consume higher current and peak power overlap problem influences on the system stability and data reliability. In this paper, current waveform is measured for erase, program and read operations, peak current and model is defined by profiling method, and estimated probability of peak current overlap among NAND devices. Also, system level TLM simulator is developed to analyze peak overlap phenomenon depending on various simulation scenario. In order to remove peak overlapping, token-ring based simple power management method is applied in the simulation experiments. The optimal peak overlap ratio is proposed to minimize performance degradation based on relationship between peak current overlapping and system performance.

• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.6
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• pp.695-701
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• 2014

Blackhole attacks having a unauthorized change of routing data will cause critical effects for transmission performance. The transmission performance will be improved to the a certain level by using or having IDS(Intrusion Detection System)/IPS(Intrusion Prevention System) as countermeasures to blackhole attacks. In this papar, the effects of IDS to ene-to-end performance of packet aggregation transmission are analyzed on MANET(Mobile Ad-hoc Network) with IDS under blackhole attacks. MANET simulator based on NS-2 is used to analyze performance parameters as MOS, connection ratio, delay and packet loss rate as standard performance parameters, an another performance factor which is suggested in this paper. VoIP(Voice over Internet Protocol) traffics, one of voice services, is used for performance analysis. A suggestion for IDS implementation on MANET with packet aggregations under blackhole is shown as one of results.