• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.3
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• pp.345-351
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• 2000

In this paper, we design and analyze a Ka-band microstrip line to rectangular waveguide transition using the expanding-cell FDTD method. The transition under investigation consists of a ridged waveguide, microstrip line, and $\lambda$/4 Chebyshev impedance transformer. To improve the accuracyand efficiency, the expanding-cell FDTD method is applied to analyze the characteristics of a ridged waveguide impedance transformer. To verify the accuracy of the expanding-cell FDTD method, S parameters of the analyzed transition are compared with those of experimental data. The efficiency of the present approach is verified by comparing the computational time for expanding-cell and that for fine cell. The relation between the number of step and operation bandwidth is analyzed by comparing the characteristics of four and three step Chebyshev waveguide impedance transformer.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.6
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• pp.551-557
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• 1997

In mobile radio environment, it is well known that the base station antenna height gain factor is 6 dB / octave. But the mobile radio environment is not simple and affected by the terrain contour or the man-made structures, so the antenna height gain factor varies due to the propagation conditions. This paper represents the received signal power gain due to the base station antenna height in the microcell environment on the basis of the flat terrain and sloping terrain model. The gain point which shows the antenna height gain is derived in this paper.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.3 no.2
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• pp.25-30
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• 2010

In this paper, a novel notch resonator is proposed based on Rectanglar Split Ring Resonator (R-RSS) element. We represented the electrical characteristics for R-SRR elements coupled with microstrip line, and measured result is compared with electromagnetic simulation (HFSS) result. We also solved equivalent circuit for R-SRR element, and also discussed influences of change structural parameters of R-SRR. the size of R-SRR is the most important parameters for frequency tuning. Also we can make tunable resonator form the basic structure. This novel resonator can apply to design of tunable bandpass filter and voltage control oscillator.

• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.2
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• pp.187-193
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• 2004

For a power source of usual electronic devices such as PDA, smart phone, UPS and electric vehicle, the battery made of serially connected multiple cells is generally used. In this case, if there are some unbalanced among cell voltages, the total lifetime and the total capacity of the battery are limited to a lower value. To maintain a balanced condition in cells, an effective method of regulating the cell voltage in indispensable. In this paper, we propose the design of a balancing circuit for electronic appliances. The balancing system was controlled by a micro-controller which enables to implement the balancing action during charging period. Proposed method has been verified by the experiment using the charger and recorder. The experimental results show that the individual battery equalization can improve battery capacity and battery lifetime and performance through an extended operational time.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.4
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• pp.624-633
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• 2018

While the multimedia lecture system has been getting smart using immerging technology, the microphone still relies on the classical approach such as holding in hand or attaching on the body. In this paper, we propose a ceiling mounted array microphone system that allows a wide reception coverage and instructors to move freely without attaching microphone. The proposed system adopts cell and handover of mobile communication instead of a complicated beamforming method and implements a wide range microphone over several cells with low cost. Since the characteristics of unvoiced speech is similar to Pseudo Noise it is shown that soft handover are possible with 3 microphones connected to delay-sum multipath receiver. The proposed system is tested in $6.3{\times}1.5m$ area. For real-time processing the correlation range can be reduced by 82% or more, and the output latency delay can be improved by using the delay adaptive filter.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2001.10a
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• pp.132-135
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• 2001

마이크로셀 시스템에서 트래픽(통화량) 성능은 가입자(사용자)들의 이동성에 민감한 영향을 받는다. 셀 내 체류시간 및 채널점유시간은 이동 속도 및 방향의 추계적인 변화에 의하여 특성지어진다. 셀 내 체류시간은 채널점유시간과 같은 통화량 성능을 분석하는데 기초적으로 이용되는 중요한 정보를 제공한다. 차세대 이동통신 네크워크로 진화해 가는 과정에서 증가하는 사용자들의 접속요청을 수용하고 주파수 효용도를 높이기 위하여 셀의 크기는 매우 작아진다. 셀의 크기가 작아질수록 통화량 성능은 사용자들, 특히 보행자들의 가변적인 이동성에 더욱더 영향을 받게된다. 단순화된 모형을 이용한 기존연구는 제2세대 이동통신에서는 수용할만한 정확성을 보였으나, 통화량 분포의 변화가 시간적으로 크고, 보행자의 이동성에 영향을 많이 받는 picocell (피코셀)의 특성을 적절히 반영하지 못하여 성능분석의 정확성을 기대하기 어렵다. 보행자의 가변적인 이동성을 수리적으로 분석하기 '위하여 랜덤 웍 (random-walk)모형을 적용하여 기존의 연구보다 개선시킨 확률모형을 제안한다. 제안된 모형으로 추계적 상관관계가 있는 보행자 이동성의 가변적 특성을 분석할 수 있다. 주요 통화량 성능지표를 제안된 모형으로 분석하였다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.251-254
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• 2006

마이크로 흐름센서는 종래의 반도체 집적회로 공정기술을 이용하여 소형으로 제작이 가능하며, 빠른 응답특성을 가지는 장점이 있어 다양한 응용이 기대되고 있다. 본 연구에서는 넓은 흐름의 세기영역에서 정밀한 감도를 가지는 2차원 마이크로 흐름센서를 실리콘 기판위에 설계하여 왔다. 이러한 흐름센서의 정확한 온도특성을 분석하고 이 결과로부터 최적을 온도 감지막 위치를 결정할 필요가 있다. 설계방법으로서 표계산 소프트웨어 Excel을 이용하여 열운송방정식의 차분 방정식을 매크로 기능을 이용하여 적용하고 워크시트 내에서 셀 참조방식을 활용하여 자동 계산을 수행하도록 구현하였다. 본 연구에서는 Excel을 활용한 효율적인 설계방법을 제시하고 하나의 히터와 양측에 한 쌍의 온도 감지막을 가진 마이크로 흐름센서에 대해서 열전달 특성을 계산하고 이로부터 최적을 온도 감지막 위치를 결정할 수 있었다.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.6
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• pp.105-113
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• 2013

In this paper a micro solar energy harvesting system with MPPT(Maximum Power Point Tracking) control using a miniature PV(photovoltaic) cell of which the output is less than 0.5V is proposed. The MPPT control is implemented using linear relationship between the open-circuit voltage of a PV cell and its MPP(Maximum Power Point) voltage such that a pilot PV cell can track the MPP of the main PV cell in real time. The proposed circuit is designed in 0.18um CMOS process. The designed chip area is $900um{\times}1370um$ including a load charge pump and pads. Measured results show that the designed system can track the MPP voltage changes with variations of light intensity. The designed circuit with MPPT control delivers MPP voltages to load even though the load is heavy such that it can supply more power when the MPPT control is applied. The proposed circuit does not require any precharged battery resulting in more suitability for miniaturized self-powered systems compared to the existing works.

• Journal of KIISE:Information Networking
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• v.29 no.2
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• pp.197-203
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• 2002

This paper proposes a new agent based mechanism called a Multicast Handoff Agent (MHA) to reduce handoff latency for IP multicast. The MHA acts as a proxy for an Internet Group Management Protocol (IGMP) of Mobile Nodes (MNs) at each Base Station (BS) and keeps information for members of multicast groups in a cell. When an MN moves to a next cell, the MHA immediately sends unsolicited reports without waiting for the IGMP query. The mechanism was evaluated through simulation and analysis and compared with the IGMPv2 for micro-mobility and the IGMP traffic. Simulation results show that handoff latency for micro-mobility can be largely reduced and the IGMP control traffic on the wireless links during the duration of membership can be eliminated. Thus, this mechanism is superior to the existing mechanism in both micro-mobility and battery duration, as the need not to reply to a query conserves battery power.

• The KIPS Transactions:PartA
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• v.19A no.2
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• pp.85-92
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• 2012

In this paper, a highly scalable real-time locating system which can measure location of fast moving targets is proposed. Within the system, the location service area is partitioned into grids with squares which is referred to as a macro-cell. Also, a macro-cell is further partitioned into $N{\times}N$ micro-cells. In a micro-cell, location reference nodes are placed on every vertex and an arbitration node is placed on the center. When a mobile node tries to measure its location, it should first communicate with the arbitration nodes for granting location measurement operation. Therefore, within a micro-cell, only one granted mobile node can calculate its location by a series of communication with location reference nodes. To evaluate performance of the proposed system, the system is modeled and simulated. The simulation result shows that the proposed system requires small communication time for location measurement operation and produces small location calculation error for fast moving targets.