• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.8
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• pp.681-687
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• 2014

Internet traffic is rapidly increasing due to the spread of personal smart devices. It causes serious burden on base stations and access points which are installed in buildings, buses, trains, and ships. We consider a communication scenario aboard a cruise ship and propose efficient contents distribution schemes to alleviate the burden of access points with multi-device-to-multi-device(MD2MD) communication. The proposed transmission method is based on the hybrid STBC-SM scheme. We compare the error performance of MD2MD communication system on the cruise ship using space-time block coding (STBC) scheme, spatial multiplexing (SM) scheme. The proposed MD2MD communication system is expected to adopt in the ship-area-network (SAN) with efficient contents distribution and reliable communication.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.1
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• pp.42-50
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• 2016

Recently, researches about the communication between LED array and the camera (alias 'Visual-MIMO'), have been actively conducted, and the application to the vehicle and a smart phone is expected to be maximized. Since the bit error may occur if the ISI is severe in a LED array, it is necessary to switch from the multiplexing to the diversity mode. In this paper, according to the use or not of a reference array pattern, a method for determining the transition time to the diversity mode is suggested and verified. When using the reference pattern, it determines the transition time to the diversity mode from the multiplexing using the brightness information of the received image. If the reference array pattern is not used, the size of LED array compared to the entire image according to the distance is used and the size of the LED array at the distance of a severe ISI may be used for the determination of transition time to the diversity. Finally, the proposed method is verified through the simulation and hardware experiments as well as by analyzing the performance in accordance with the ISI level and the distance.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.10
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• pp.1869-1876
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• 2006

Recently, STC techniques have been considered to be candidate to support multimedia services in the next generation mobile radio communications and have been developed the many communications systems in order to achieve the high data rates. In this paper, we Nose the Trellis-Coded Differential Space Time Modulation system with multiple symbol detection. The Trellis-code performs the set partition with unitary group codes. The Viterbi decoder containing new branch metrics is introduced in order to improve the bit error rate (BER) in the differential detection of the unitary differential space time modulation. Also, we describe the Viterbi algorithm in order to use this branch metrics. Our study shows that such a Viterbi decoder improves BER performance without sacrificing bandwidth and power efficiency.

• The Journal of the Acoustical Society of Korea
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• v.16 no.6
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• pp.100-105
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• 1997

To analyze the multipath propagation effects on the source bearing detection of HLA(Horizontal Line Array), the conversion mechanism of the multipath into the bearing is described, and the bearing is estimated from the multipath modeled with typical sound velocity structures of the East and the South Sea of Korea. The erroneous bearing is observed from the beamforming outputs simulated with the modeled multipath, and the erroneous phenomena are analyzed. In case of the East Sea, since the multipath propagation with a high receiving angle occurs due to strong inverse slope of the sound velocity structure, it is possible that the estimated source bearing is different from the real source bearing, and that the number of the source is misrecognized.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.3A
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• pp.248-255
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• 2008

In an OFDMA system the performance of multi-user scheduling in the frequency domain is affected by the frequency selectivity of the channel. If the channel is too flat in the frequency domain, the multi-user scheduling gain might be degraded. On the contrary, if the frequency selectivity is too high and the magnitude of the frequency response severely fluctuates on the allocation bandwidth, it is also hard to get sufficient scheduling gain. For maximizing the multi-user scheduling gain, a cyclic delay diversity technique can be used to adjust the frequency selectivity of the channel. This paper proposes a method to determine the optimal delay value of cyclic delay diversity according to the allocation bandwidth and the channel characteristics.

• The Journal of the Acoustical Society of Korea
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• v.27 no.7
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• pp.342-349
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• 2008

Multipath makes clear message transfer difficult in the underwater communication. To solve this problem, we propose a new method producing proper MFSP (Modulation Frequency Shift Period) which could be obtained by calculating time delay caused by different path from a transmitter to a receiver. At the transmitter end, messages were divided according to the size of the MFSP and transmitted accordingly alternating Frequency. At the receiver end, the received messages were demodulated in order to recover the original message by the adaptive BISMO algorithm which is constructed at the algorithm design stage. Adaptive MFSP and estimated BER (Bit Error Rate) were calculated through simulation test.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.101-106
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• 2006

Digital technology has been applied to marine seismic survey to develop data processing technology and multi-channel marine seismic survey. In result, high-resolution marine seismic survey ended in a success. Surveys are conducted for various purposes using various frequencies of acoustic sources. A low frequency source is used for deeper penetration and a high frequency source is used for higher resolution survey. In this study, a multi-source system was used for multi-channel marine seismic survey to acquire seismic sections of both low and high frequencies. Variations of depth of penetration and resolution would be used to achieve more accurate analysis of formations. In this study, the multi-source system consists of Bubble Pulser (400 Hz) for low frequency source and Sparker (1.5kHz) for high frequency source.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2003.09a
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• pp.601-604
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• 2003

방사성폐기물 처분 연구의 일환으로 화강암지역내 500m 심도의 심부시추공이 착정되었으며, 다중패커시스템이 설치되어 장기적으로 심도별 지하수의 수리 및 화학특성이 모니터링 되고 있다. 지하수 수두값의 심도별 특성은 천부에서 심도 250m까지는 대체로 감소하는 경향을 보이며 250m이하에서 500m 심도까지는 증가하는 경향을 보여준다. 각 심도구간에서의 지하수 수두값은 장기적으로 일정한 값을 보여주지만, 장마기간동안 집중적으로 모니터링된 결과에 따르면 심도 370m 상부에서는 지하수 함양변화에 따라 지하수 수두가 변화되는 반면, 심부구간에서는 지하수 함양변화에 대하여 영향을 받지 않음을 보여준다.

• Proceedings of the KSRS Conference
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• 2008.03a
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• pp.119-124
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• 2008

2000년대 들어 주기적으로 발생하고 있는 봄 가뭄에 대한 적절한 대책 마련을 위해서는 가뭄을 모니터링 할 수 있는 감시체계가 필요하며 가뭄의 심도를 정량적으로 나타내기 위한 지표가 요구된다. 또한, 가뭄의 거동 및 지역적인 심도 분석을 위해서는 면 단위의 공간적인 분석이 요구된다. 위성영상은 공간정보를 신속하고 주기적으로 제공할 수 있는 도구로 위성영상의 밴드 조합을 통해 제작된 식생지수는 1990년대 중반 이후 건조지역을 중심으로 가뭄 모니터링을 위한 도구로 활용 중이다. 본 연구에서는 MODIS 영상으로부터 제작된 정규식생지수(NDVI)를 이용하여 식생상태지수(VCI)와 정규화된 식생지수(SVI)를 제작하였으며 2000년$\sim$2007년을 대상으로 가뭄발생연도, 각 가뭄사상에 대한 심도, 가뭄다발 시기 및 다발지역을 분석하였다.

• Proceedings of the Korean Society of Disaster Information Conference
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• 2022.10a
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• pp.121-123
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• 2022

본 현대사회는 문명적, 기술적, 산업적으로 발전함에 따라 그에 상응하는 절도, 폭행, 살인 등 중대범죄의 범위를 벗어나 이념과 국가, 종교, 등 가치관과 사상에 따른 테러 사건 등 국제적인 범죄도 증가하고 있는 추세이며, 국제사회는 중대범죄 및 전쟁의 공포보다 예측 불가능, 막대한 대량 피해를 불러오는 테러에 의한 공포심을 더 비중 있게 대하는 현실에 직면했다. 테러범죄는 개인을 넘어 다중에게 피해를 입힐 수 있는 범죄인만큼 대중에게 경각심과 위험성을 알리기 위해선 구체적이고 손쉽게 이해할 수 있는 명확성이 필요하다. 테러는 수년간 다양한 방식과 개념들이 증식했으며 피해 또한 더 이상 소규모인원, 특정인을 향한 계획적인 범행에서 불특정 다수를 향한 뉴테러리즘식의 테러로 발전하고 있어 안보의 개념에도 영향을 미치고 있다. 따라서 대한민국 역시 언제까지나 테러의 위험성으로부터 안전을 확신할 수 없기 때문에 국내 정서에 맞는 테러 대응방안과 시스템 구축을 통해 뉴테러리즘의 발생 가능성을 염두 하고 대비할 필요가있다.