• The Journal of the Korea institute of electronic communication sciences
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• v.12 no.1
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• pp.75-84
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• 2017

It becomes more and more more important for the storage that supports high speed recording and stable access from network environment. As one field of basic science which produces massive astronomical data, VLBI(: Very Long Baseline Interferometer) is now demanding more data writing performance and which is directly related to astronomical observation with high resolution and sensitivity. But most of existing storage are cloud model based for the high throughput of general IT, finance, and administrative service, and therefore it not the best choice for recording of big stream data. Therefore, in this study, we design storage system optimized for high performance of I/O and concurrency. To solve this problem, we implement packet read and writing module through the use of libpcap and pf_ring API on the multi core CPU environment, and build a scalable storage based on software RAID(: Redundant Array of Inexpensive Disks) for the efficient process of incoming data from external network.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.94.1-94.1
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• 2012

천리안위성은 우리나라 최초의 정지궤도복합위성(COMS: Communication, Ocean, and Meteorological Satellite)으로 2010년 6월 27일, 남미 기아나 쿠루기지에서 아리안-5 로켓에 의해 발사된 후 동경 128.2도, 적도 상공 약 35,800 km 고도의 정지궤도에 안착되었다. 이 후 궤도상시험 기간과 안정화 기간을 거쳐 2011년 4월 1일, 기상청은 위성자료 서비스를 시작하였다. 천리안위성의 기상영상기는 한반도 주변의 기상변화와 전 지구적 기후 변화 및 대기 운동을 감시하기 위해 실시간 관측 및 전송 시스템을 갖춘 탑재체이다. 이 기상영상기는 하루 8번의 지구 반면 영역과 각각 80번 내외의 북반구 및 한반도 영역을 관측하며, 이 자료는 지상에서 복사보정과 기하보정을 거친 후 위성을 통해 다시 사용자에게 배포된다. 천리안위성 기상영상기는 쉼 없이 관측하고, 일정 시간 이내에 그 자료를 배포해야 한다. 이러한 자료서비스는 운영시스템의 장애나 자연현상에 의한 자료 미수신 혹은 미처리가 발생할 경우 운영 결과 및 성과에 영향을 미친다. 이와 같은 장애에 대비해 국가기상위성센터는 이중화된 시스템을 구축했으며, 자료 백업 부기관으로서 한국항공우주연구원과의 사이트 이중화도 시행하고 있다. 그러나 정지궤도에 있는 위성과 태양 및 지구의 역학적인 관계에 따라 태양 전파 잡음의 영향인 태양간섭과, 위성 태양전지판 충전 장애를 일으킬 수 있는 위성식, 그리고 위성 자정 주변에 발생할 수 있는 태양광 침입 및 산란광 영향 등은 미리 예측되어야 하며, 이 시기 운영 방안 마련과 사용자 공지 등의 조치가 수반되어야 한다. 국가기상위성센터는 춘 추분 시기에 발생하는 이러한 태양 영향을 예측하고 검증했으며, 이 시기 위성 및 지상국의 효율적인 운영방안을 마련하였다.

• Journal of IKEEE
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• v.6 no.1 s.10
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• pp.40-46
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• 2002

In this paper, a microstrip array antenna is designed, fabricated and measured for ETCS(Electronic Toll Collection System). To reduce effect of external propagation environment, we use edge-cuffed element and to obtain wider axial ratio and increased bandwidth, we use the sequential rotation array method. Also to fulfill ETCS, roadside equipment are designed to be provide a radiation pattern which can accurately pinpoint the designated communication area without interference of another lanes. And we make and apply an absorber to the array antenna to reduce SLL(Side Lobe Level). From the measurement, we get that return-loss at center frequency is -20.675dB, axial ratio is 0.35dB and the gain is 20.26dBi. And we found that SLL is reduced.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2002.11b
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• pp.69-69
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• 2002

갯대추(Paliurus ramosissimus (Lour.) Poiret)는 갈매나무과에 속하는 낙엽관목으로 드물게 교목으로 자라며, 우리나라에서는 제주도에만 분포하는 것으로 알려진 희귀식물이다. 이 종의 주요 분포대는 동아시아의 열대 및 아열대로 제주도는 위도 상 북한계로 알려져 환경부 지정 보호식물 제 39호로 지정\ulcorner보호하고 있으나 자생지에 대한 구체적인 조사가 이루어진 바 없다. 따라서 본 연구는 자생지의 현황과 생육상황을 파악하여 자생지 보전에 기여하고자 실시하였다. 갈매나무과는 세계적으로 58속 900여종이 분포하고, 갈매나무속(Genus Rhamnus), 헛개나무속(Genus Hovenia), 대추속(Genus Zyzyphus) 등이 주요 속으로 알려져 있으며, 그 중 갯대추속(Genus Paliurus)은 과실이 건과이고 날개가 있는 특징으로 다른 속과 구별된다. 꽃은 양성화로 7월~9월에 피고, 화서는 수 개의 꽃이 달리는 취산화서, 열매는 반구형으로 과병에 연한 갈색의 복모가 있으며 얕게 3부분으로 갈라져 각 실마다 편평한 공모양의 종자가 1개씩 들어있다. 갯대추 자생지는 제주도의 동부지역인 북제주군 구좌읍 김녕에 1개소, 남부지역인 남제주군 남원읍 태흥에 1개소, 서부지역인 북제주군 한경면 용당에 1개소, 한경면 용수에 1개소, 한경면 신창에 3개소 및 남제주군 대정읍 일과에 2개소 등 총 6지역 9개소였다. 분포지는 해발 20m이하의 해안가 토심이 얕은 암반 위였으며, 주로 해수의 영향을 직접적으로 받는 곳이었다. 생육상황을 조사한 결과 바다 쪽으로 갈수록 수고가 급격히 낮아지는 경향을 보였으며, 최소 0.3m, 최대 4.5m였고 평균 1.6m 정도였다. 수반종으로는 순비기나무와 갯기름나물, 갯까치수영 등 해안식생의 구성종이 대부분이었으며, 돌가시나무, 상동나무 등도 혼생하는 것으로 조사되었다. 자생지 위협요인으로는 양식장 시설, 도로개발, 해안매립 및 쓰레기 투기 등과 같은 인위적 간섭과 상동나무 등 주변식물의 피압이 주 요인이었다. 한편 갯대추는 희귀식물로서 뿐만 아니라 해류에 의해 전파되는 종으로 알려져 있어 제주도의 식물지리학적 연구에도 좋은 연구대상이 되고 있으므로 종 보전대책 및 자생지 보호에 대한 추가적인 연구가 필요하다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.9
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• pp.783-790
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• 2016

Since scarcity of spectrum in future mobile networks, millimeter wave frequencies from 30 GHz to 300 GHz have been proposed to be used in an important part of 5G mobile communication backhaul links to provide several giga bits services. In ITU-R has been invited to conduct and complete in time for WRC-19 the appropriate studies to determine the spectrum needs for the terrestrial component of IMT in the frequency range between 24.25 GHz and 86 GHz. Also, small cells such as a femtocell, and heterogeneous networks have been deployed through world in order to enhance the communication capacity. At this stage, it is important to develop millimeter wave frequencies to provide 5G mobile broadband services, and thus this paper proposes the effective usage of these frequencies by summarizing the FCC allocation of millimeter waves, their propagation characteristics, the required minimum path length, and the interference effect.

• Aerospace Engineering and Technology
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• v.6 no.2
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• pp.79-86
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• 2007

In order to operate Low Earth Orbit(LEO) satellite on space, technical requirements and administrative procedure which are defined by the International Telecommunication Union(ITU) should be followed on satellite development. Main technical requirements to follow are purpose of use, bandwidth, Radio Frequency(RF) intensity, and constraints on new satellite network about existing satellite networks according to frequency spectrum. Such ITU's requirements are reflected and designed on system specification and space to ground interface control document. In order to have a right and protection about using the satellite network on space, the satellite network has to be registered on Master International Frequency Register(MIFR) and procedure for this has to be followed. Coordination with countries raising objection is needed in order to register. And reference and method for coordination are also needed.

• Journal of Advanced Navigation Technology
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• v.18 no.1
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• pp.7-13
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• 2014

In this paper, an effect on a GPS receiver by spoofing signal is analyzed and a GPS spoofing signal detection algorithm for GPS L1 C/A spoofing signal is proposed. A proposed detection algorithm monitors the correlation function distortion by the spoofing signal. If detected distortion is over a detection threshold, we can determine that the spoofing signal is received. The detection threshold is calculated from the statistical characteristics of a thermal noise. For verifying the suggested algorithm, a MATLAB-based simulation platform is implemented. This platform has functionalities to track GPS signal and measure the correlation values. By using this platform, the correlation function distortion by spoofing signal is observed. Also a performance of the algorithm proposed in this paper is applied and confirm the detection of a spoofing signal.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.6
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• pp.723-729
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• 2014

When the bluetooth technology of smartphone is applied to a remote control system, communication errors caused by wave attenuation and interference results in the shortening of communication distance, loss of the target device control and malfunctioning. In this study, we propose a method to adopt a retransmission persistence controlled S/W ARQ in bluetooth communication to minimize the effect of the communication failure and to detect and handle the state where the target device gets lost control. We implemented a motor-driven RC car equpped with a bluetooth communication module and a steering application program on smartphone to test the proposed method. The experiments are conducted in three communication environments, and have resulted in the increase of the communication distance by at least 30% when S/W ARQ is applied. Moreover, when the communication was disrupted due to environmental disturbances, the S/W ARQ based system stopped immediately any undergoing operations to avoid possible malfunction.

• Journal of Korea Water Resources Association
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• v.49 no.1
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• pp.51-60
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• 2016

The purpose of this study is to examine the control function of discharged flow due to the shape and plane arrangement of permeable submerged breakwater. For the discussion on it in detail, 3-dimensional numerical model based on PBM (Porous Body Model), which is able to simulate directly interaction of Fluid Permeable structure Seabed has been used to simulate water discharge in a NWT (Numerical Water Tank). To verify the applicability, LES-WASS-3D is analyzed comparing to the experimental result about propagation characteristics of dam-break wave through a permeable structure. Using the results obtained from numerical simulation, the effects of the shape and plane arrangement of submerged breakwater on reducing velocity and flow induction have been discussed related to the mean flow distribution and vertical distributions of horizontal velocities around ones.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.4C
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• pp.351-363
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• 2006

The 8-VSB modulation, the transmission standard for the terrestrial digital television(DTV) of the Advanced Television Systems Committee(ATSC), suffers from multipath fading because it conveys information on the amplitude. To solve this problem, decision feedback equalizers(DFE's) have been commonly used in terrestrial DTV receivers. However, under severe channels, such as a 0 dB ghost channel or a single frequency network (SFN) channel, the DFE shows unstable convergence due to the error propagation caused by decision errors. Instead of unstable time-domain DFE schemes, by proposing a frequency-domain direct-inversion equalization method, we try to guarantee stable equalization and achieve low symbol error rates. To secure the existence of a channel inverse, channel-matched filtering and noncausal filtering are carried out prior to equalization. Simulation results show that the proposed method performs much better than existing DFE schemes in terms of both the stability and the symbol error rate.