• Membrane Journal
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• v.25 no.2
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• pp.162-170
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• 2015

In this study, gas permeability of polyimide materials having a various amine group was measured and molecular dynamics was used to analyze the dynamic characteristics of the gas molecules in the polyimide by calculating the position and velocity of the gas molecules with change of the time. The gas permeability of polyimide membrane having substitution site which increase free volume in the polymer was increased. However, polyimide with rigid structure showed decreased gas permeability. As a result of analyzing the change in the gas permeation behavior using molecular dynamics simulations, we confirmed that the results show the same tendency with actual measurements of the gas permeability.

• The Journal of the Korea Contents Association
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• v.10 no.12
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• pp.10-17
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• 2010

In this paper, we design digital D-PHY link chip controling DSI (Display Serial Interface) that meets MIPI (Mobile Industry Processor Interface) standard. The D-PHY supports a high-speed (HS) mode for fast data traffic and a low-power (LP) mode for control transactions. For low power consumption, the unit blocks in digital D-PHY are optionally switched using the clock gating technique. The proposed low power digital D-PHY is simulated and compared with conven tional one about power consumption on each transaction mode. As a result, power consumptions of TX, RX, and total in HS mode decrease 74%, 31%, and 50%, respectively. In LP mode, power reduction rates of TX, RX, and total are 79%, 40%, and 51.5%, separately. We implemented the low power MIPI D-PHY digital chip using $0.13-{\mu}m$ CMOS process under 1.2V supply.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.1
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• pp.275-281
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• 2012

Community network is a communication environment where heterogeneous devices can access and communicate with each other at any time and at any space to share information. To do so, mobile devices are required to be self-configured even in absence of communication infrastructures. Semi-infrastructured wireless ad-hoc network is a promising solution to meet with such a requirement. This paper proposes the VTC(virtual topology coordinator) system as an evaluation tool for examining network protocols that are intended to be deployed in the semi-infrastructured ad-hoc networks. VTC emulates multi-hops wireless network topology virtually using a mechanism of selective receiving MAC frame in a small area, where only a single hop communication is available. VTC system cannot consider all properties introduced in real wireless network, but do more wireless properties than verification through simulation.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.5
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• pp.249-258
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• 2013

In multi-hop ad hoc networks, multi-interface multi-channel architecture is being noticing as methodology to improve the effective bandwidth and end-to-end throughput, But since existing routing metrics designed for networks based on single-interface exactly can not reflects the nature of networks based on multi-interface multi-channel, we are not expected the effect of throughput improvement. there had been proposal of MCR that discover high throughput by using metrics such as channel diversity and interface switching cost. however, MCR have an problem that is degraded it's performance in congested networks, because it not reflects the impact of traffic load. in this paper, we propose MAMCR metric, which select high throughput paths under congested conditions by combination MCR with channel access time metric, and conform it's the effect of performance improvement by ns-2 simulation.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.4
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• pp.51-57
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• 2020

WSN is a wirelessly configured network of sensor nodes with limited power such as batteries. If the sensor node's battery is exhausted, the node is no longer available. Therefore, if the network is to be used for a long time, energy consumption should be minimized. There are many Wireless Sensor Network Protocols to improve energy efficiency, including Cluster-based and chain-based Protocols. This paper seeks to examine the performance evaluation of routing protocols studied separately for the improvement of performance in wireless sensor network. The criteria for comparison were selected as the LEACH protocol, a representative hierarchical routing protocol, and the comparison targets considered CHEF and FLCFP and LEACH-DFL routing protocols with Fuzzy Logic. Various criteria for performance comparison were presented in this paper, and the performance was compared through simulation of each protocol. The purpose is to present a reference point for comparing the performance of other protocols through the performance comparison of CHEF, FLCFP, and LEACH-DFL, protocols with LEACH and Fuzzy Logic, and to provide additional design methods for improving the performance of protocols.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.6
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• pp.85-94
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• 2015

In this paper, an enhanced QoS multicast routing scheduling scheme is proposed to adapt to a dynamic mobile traffic condition for wireless mesh networks (WMNs). It handles the network QoS by controlling the delay constraints for multimedia applications. The group size will be controlled according to both the current network state and QoS requirements. The dynamic reconstruction of QoS multicast tree can be obtained from preprocessing with both the partial multicast routing scheme and the traffic estimation. Performance evaluation of the proposed scheme is carried out on randomly generated graph derived from the wireless mesh network, by choosing the optimal value related to the appropriate delay bounds. Simulation results show that the proposed scheme can improve the performance of QoS multicast routing for WMNs.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.11
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• pp.1256-1263
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• 2012

Assigning different frequency resources among adjacent cells, namely the frequency reuse technique can be utilized to mitigate intercell interference, which is a major cause of performance degradation in cellular systems. Since most of conventional frequency reuse patterns are limited to the two-dimensional environment, the research for the three-dimensional frequency reuse would be beneficial especially for the implementation of femto cells in downtown office buildings. We propose frequency reuse patterns in three-dimensional space and evaluate their performance of each pattern in terms of channel capacity. In particular, we show that the proposed three-dimensional frequency reuse patterns can be applied for carrier-aggregated transmission of LTE-Advanced systems. The performance of the proposed patterns is evaluated using computer simulation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.11
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• pp.978-986
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• 2016

X-band phased array antenna module for the compensation of deformed beam direction by wing deformation is designed and fabricated. The phased array antenna module consists of array antenna, phase shifter, power divider and control circuit. To select out the best component, the variation of radiation pattern by wing bending and phase error of components is simulated. The fabricated phased array antenna module shows an antenna gain of 5.84 dBi, a return loss of 13.6 dB and a bandwidth of 10.6 % at 9.375 GHz. The test bed was set up to verify the performance of beam direction compensation. This test confirmed that the main beam direction of array antenna has been well restored under wing bending of 9 %.

• Journal of IKEEE
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• v.18 no.2
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• pp.214-219
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• 2014

In this paper, the usage of tilt-implanted trench Schottky diode(TITSD) based on silicon carbide is proposed. A tilt-implanted trench termination technique modified for SiC is proposed as a method to keep all the potentials confined in the trench insulator when reverse blocking mode is operated. With the side wall doping concentration of $1{\times}10^{19}cm^{-3}$ nitrogen, the termination area of the TITSD is reduced without any sacrifice in breakdown voltage while potential is confined within insulator. When the trench depth is set to 11um and the width is optimized, a breakdown voltage of 2750V is obtained and termination area is 38.7% smaller than that of other devices which use guard rings for the same breakdown voltage. A Sentaurus device simulator is used to analyze the characteristics of the TITSD. The performance of the TITSD is compared to the conventional trench Schottky diode.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.3
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• pp.45-52
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• 2006

In this paper, we analyze on the effect of LCR filter to mitigate transient overvoltage on the high voltage induction motor fed by H-bridge cascaded 7-level inverter. The switching surge voltage that it was occurred in inverter appears transient overvoltage at the motor input terminal. the transient overvoltage becomes the major cause to occur the insulation failure by serious voltage stress in the stator winding of high voltage induction motor. The effect of transient overvoltage appears more serious in high voltage induction motor than low voltage induction motor. We selected LCR filter for reduction of the transient overvoltage. Consequently, we demonstrated that the LCR filter connected to the invertor output terminals greatly reduces the transient voltage stress and ringing. The results of simulation show the suppression of transient overvoltage at the motor end of a long cable. using EMTP