• Proceedings of the Korea Information Processing Society Conference
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• 2000.10b
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• pp.1557-1560
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• 2000

이동 통신 분야에서 통신 기술의 발달에 의한 정보화 사회의 진전에 따라 비약적인 발전을 거듭하고 있다. 특히 이동 전화와 노트북과 같은 이동 단말기가 보편화됨으로써 셀룰러망이 빠르게 성장할 수 있었고, 제한된 라디오 스펙트럼에서 이동 단말기의 증가하는 수를 조정하기 위해 마이크로/피코셀룰러 구조와 같이 디자인되었다. 이와 같이 다수의 사용자를 수용하기 위해 셀 크기를 축소하게 되면 핸드오프 이벤트가 증가하게 되고 안정적인 서비스를 제공하기 위해 효과적으로 처리해 줄 수 있는 핸드오프 기술은 필수적이라 할 수 있다. 이 논문에서는 이웃에 있는 셀에 셀룰러 트래픽의 양에 따라 핸드오프 호에 예약한 셀 안에 대역폭의 양을 동적으로 조정하는 Population-Based Reservation구조에서의 Fractional Parameter에 대한 성능을 분석하였다. 이 파라미터의 값은 QoS 요구를 기본으로 결정되어져야 하고 요구사항을 충족시키기 위해 변화하는 트래픽 상태들에 따라 동적으로 조절되어질 수가 있다.

• Journal of the Korea Society of Computer and Information
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• v.15 no.8
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• pp.79-87
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• 2010

It is widely accepted that the coverage with high user densities in mobile multimedia environments can only be achieved with small cell such as micro- and pico-cell. If handover events occur during the transmission of multimedia, the efficient resource reservation and handover methods are necessary in order to maintain the same QoS of transmitted multimedia traffic because the QoS may be defected by some delay and information loss. In this paper, we propose a resource allocation method in the next generation mobile communication systems, in which the resource allocation process has a tight relation with call admission, call load, and packet scheduling. The simulation results show that our proposed method provides a excellent performance.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.149.2-149.2
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• 2012

세계전파통신회의 (WRC; World Radiocommunication Conference)회의는 국제전기통신연합 (ITU)에서 규정하는 국제 전파법 제개정을 위해, 3-4년 간격으로 개최되는 전파통신 관련 최고회의라고 할 수 있다. WRC-15회의는 2015년 11월 2일 - 11월 27일에 걸쳐 스위스 제네바에서 개최될 예정이며, 과학업무 관련 의제들은 다음과 같다. 즉, 7145-7235 MHz 또는 7-8 GHz 대역의 지구탐사위성(지구대우주)업무의 1순위 분배연구, 지구탐사위성업무용 연속 600MHz 대역 분배방안 연구 (8,700~10,500MHz대역 내), 우주선 근거리통신용 관련 규정 재검토, 윤초삭제와 관련된 세계협정시(UTC) 개정 또는 대처방안 연구가 있다. 그리고 모바일광대역 응용 실현을 위한 이동통신업무 추가 분배 및 IMT 추가 지정 연구, 7150-7250MHz (우주대지구), 8400-8500MHz (지구대우주)에서 고정위성업무 추가 분배연구, 나노 위성 및 피코 위성 규제 관련 연구들이 있다. 따라서 본 발표에서는 WRC-15회의의 과학업무 의제들 가운데, 국내전파망원경 운용에 영향을 미칠 수 있는 주파수 대역 및 윤초 관리 등과 관련된 주요 과학업무 의제를 소개하고 이에 대한 향후 대응책 검토를 하고자 한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.1A
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• pp.7-16
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• 2003

Handover is very important to support the mobility of user because wireless ATM networks have smaller cell size such as micro/pico cell for broadband mobile multimedia service In this paper, we propose dynamic path reservation handover scheme for fast inter-MSC (Mobile Switching Center) handovers To reduce the handover delay for connection re-routing, the proposed scheme reserves virtual channels from nearest common node to neighbor MSC in advance Especially, our handover scheme predicts the number of inter-MSC handover calls at each period by the prediction algorithm and reserve virtual channels The simulation and analysis results show that our scheme reduce handover complexity and has higher reservation channel utilization, compared with DVCT scheme.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.590-593
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• 2005

In this paper, it is analyzed a transmission time of ACL Packet in bluetooth wireless link. In order for segment to improve the transfer capability in bluetooth system, it is fragmented in TCP total messages that are coming down from upper layer and then the packets are sent one at time in baseband. And it is studied that transmission time for bluetooth wireless link according to DM1, DM3 or DM5 packet type in bluetooth piconet environment. From the results, we were able to obtain ACL packet transmission time, optimal TCP packet size and DM packet size.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.1000-1002
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• 2005

In the Bluetooth piconet in which up to 7 slave devices can be connected simultaneously at one network instance, the wireless data expected to be sent over to the RF interface should be sliced by the unit of 1 micrometer, which is a requirement in the specification of the Bluetooth version 1.1. In this contribution, we have designed a digital low-pass filter which is able to slice the unstable analog signal fed from the RF interface to the Baseband, by the uniform unit of 1 micrometer, and is also capable of removing the possible noise which can be caused by the analog circuit system. The low-pass filter operated well in the various modes of the Bluetooth RF embedded Baseband chip such as sleep mode, normal mode, and high-speed mode at 12MHz, 24MHz, and 48MHz respectively.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.10
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• pp.1009-1015
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• 2013

Ultra-short laser pulses are effective, when high requirements concerning accuracy, surface roughness and heat affected zone are demanded for surface structuring. In particular, picosecond laser systems that are suited to be operated in industrial environments are of great interest for many practical applications. This paper focused on inducing optimum process parameters for higher volume ablation rate by analyzing a relationship between crater diameter and optical spot size. In detail, the dependency of the volume ablation rate, penetration depth and threshold fluence on the pulse duration 8 ps and wavelength of 515 nm was discussed. The experimental results showed that wavelength of 515 nm resulted in less threshold fluence ($0.075J/cm^2$) on copper than IR wavelength ($0.3J/cm^2$). As a result, it was possible that optimum fluence for higher volume ablation rate was achieved with $0.28J/cm^2$.

• Proceedings of the Korean Society of Computer Information Conference
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• 2011.06a
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• pp.397-400
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• 2011

본 논문은 로봇 교육에 대한 연구의 동향 파악을 목적으로 학술연구정보서비스(RISS)를 활용하여 2000년부터 2011년까지 발간된 로봇 교육관련 국내학술지논문 119개를 분석하였다. 구체적인 조사 영역은 활용된 로봇의 종류, 연도별 논문 발행 수, 주제, 연구 대상, 적용교과, 연구방법으로 나누고 가장 많이 다루어지고 있는 연구 부분을 파악하였다. 주로 각 논문의 초록을 면밀히 분석하였으며 모호하다고 생각이 들 경우에는 논문 내용을 확인하였다. 연구 결과 로봇 교육 관련 연구는 해가 갈수록 증가하는 추세에 있으며 연구 방법으로는 양적 연구가 주를 이루지만 2007년 이후 질적 연구와 통합 연구 또한 증가하고 있었고, 로봇은 21가지 중에 주로 사용되는 것이 NXT와 피코 크리켓, iRobiQ였다. 연구 주제는 고차원적인 사고와 정서적인 측면을 측정하는 로봇 활용 교육이 다수를 차지하였고, 대상은 주로 초등학생에 집중되어 있었다. 연구에 적용된 교과를 살펴보면 주로 정보교과와 재량활동이나 방과후 활동, 통합교육 순이었다.

• Journal of ILASS-Korea
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• v.25 no.4
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• pp.145-153
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• 2020

The purpose of this study is to compare the injection and spray characteristics of single-hole GDI injectors using injection rate and mie-scattering spray images. Five types of single-hole injectors with different nozzle hole diameters were used, and the spray rate, spray tip penetration, spray area, and spray width were analyzed. As a result, the diameter of the nozzle hole had a direct effect on the injection and spray characteristics. It was confirmed that the larger the diameter of the nozzle hole, the higher the injection quantity, the spray tip penetration, the spray area, and the spray width. In addition, it was confirmed that the near-field spray, which has little influence of ambient air, has a great correlation with the injection rate.

• Journal of ILASS-Korea
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• v.25 no.4
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• pp.154-161
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• 2020

A single spray plume is the basic unit of the entire spray plume and is an important factor in understanding the spray characteristics. However, since the multi-hole GDI injector has a narrow spray angle, the superposition of the spray plumes occurs severely. Therefore, the spray uniformity and the spray atomization characteristics of a single spray plume were analyzed in this study using a single-hole GDI injector. Five single-hole GDI injectors with different nozzle hole diameters were used in the experiment. The uniformity of the spray was evaluated through the analysis of the spray pattern images. In addition, the atomization characteristics were compared using the diameter distribution of the spray droplets obtained using PDPA. As a result, the larger diameter of the nozzle hole, the less uniformity of the spray, and the injection pressure did not have a significant effect on the spray uniformity. It is judged that the surface roughness of the injector has a greater effect on spray uniformity than the diameter of the nozzle hole. Also, the size of the spray droplets increased sharply when the diameter of the nozzle hole was 230 ㎛.