• Journal of the Optical Society of Korea
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• 제19권5호
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• pp.514-520
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• 2015

This paper presents a novel shore-to-sea maritime data transmission system based on time-code diversity, using visible light in maritime environments to overcome the limitations of conventional maritime wireless communications. The proposed system is primarily comprised of existing LED-based lighthouses and maritime transceivers (marine beacons, buoys, etc.), and thus is considered cost-effective in terms of implementation. We first analyze maritime visible-light communications on the basis of the unique properties of a maritime environment, i.e. sea states (wave height, wind speed, etc.), plus atmospheric turbulence, using the Pierson-Moskowitz (PM) and JONSWAP (JS) spectrum models. It is found that the JS model outperforms the PM model, and that the coverage distance depends on the LED power and sea states. To combat maritime fading conditions that significantly degrade performance and coverage distance, we propose a time-code diversity (TCD) scheme in which the delayed versions of the original data are retransmitted using orthogonal Walsh codes. This TCD scheme is found to be superior, in that it offers three orders of magnitude in terms of BER performance, compared to a conventional (non-TCD) transmission scheme. The proposed scheme is robust and efficient in overcoming the effect of impairments present in maritime environments with a BER of approximately $10^{-5}$and a data rate of 100 Kbps at a distance of 1 km.

• Earthquakes and Structures
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• 제10권1호
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• pp.53-71
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• 2016

Unconventional computer vision and image processing techniques offer significant advantages for experimental applications to shaking table testing, as they allow the overcoming of most typical problems of traditional sensors, such as encumbrance, limitations in the number of devices, range restrictions and risk of damage of the instruments in case of specimen failure. In this study, a 3D motion optical system was applied to analyze shake table tests carried out, up to failure, on a natural-scale masonry structure retrofitted with steel reinforced grout (SRG). The system makes use of wireless passive spherical retro-reflecting markers positioned on several points of the specimen, whose spatial displacements are recorded by near-infrared digital cameras. Analyses in the time domain allowed the monitoring of the deformations of the wall and of crack development through a displacement data processing (DDP) procedure implemented ad hoc. Fundamental frequencies and modal shapes were calculated in the frequency domain through an integrated methodology of experimental/operational modal analysis (EMA/OMA) techniques with 3D finite element analysis (FEA). Meaningful information on the structural response (e.g., displacements, damage development, and dynamic properties) were obtained, profitably integrating the results from conventional measurements. Furthermore, the comparison between 3D motion system and traditional instruments (i.e., displacement transducers and accelerometers) permitted a mutual validation of both experimental data and measurement methods.

• 한국통신학회논문지
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• 제37권8B호
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• pp.706-711
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• 2012

기존의 LED (Light Emitting Diode)를 이용한 가시광 통신방식은 주로 수 m 의 짧은 전송거리와 수백 Mb/s 이하의 낮은 전송속도를 보여왔다. 이를 타개하기 위하여 본 논문에서는 MIMO (Multiple-Input Multiple-Output) 기술을 가시광 통신에 적용하고자 하는 연구를 수행하였다. 빛은 RF 주파수와는 물리적 특성이 다르기 때문에 기존의 RF 주파수에서 사용되던 MIMO 기술의 이론을 그대로 가시광 통신에 적용하기는 힘들다. 따라서, 본 논문에서는 렌즈를 이용하여 물리적으로 광신호를 분리하고, 이미지 센서를 수신기로 사용하여 MIMO 기술을 구현하는 방식을 채택하였다. 본 논문에서는 상용 이미지센서를 이용하여 채널당 200 bit/s의 전송속도 및 전송거리 10.5 m의 장거리 $2{\times}2$ MIMO LED 무선 가시광 통신 실험을 구현하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제37권4호
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• pp.425-430
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• 2013

수중통신은 지상통신에 비하여 통신채널의 강건성과 고속데이터 전송 측면에서 상당한 제약 요인을 가지고 있다. 공기 중에서 RF 통신은 장거리 전송에도 높은 데이터 전송률을 보이지만, 수중에서는 매질의 전도특성으로 인하여 전파에너지의 심각한 감쇠현상이 발생하여 통신이 어려운 실정이다. 현재 수중에서 수 십 킬로미터 이상의 장거리 통신이 가능한 음향파 통신 모뎀이 개발되어 사용되고 있지만 낮은 전송율과 높은 전력 소모, 느린 전송속도가 문제로 거론되고 있다. 이 문제를 보완할 수 있는 방안으로 빛을 이용한 근거리 수중무선통신이 대안으로 연구되고 있다. 본 논문에서는 가시광 파장영역에서 수중통신 채널 특성을 분석하였다. 자유공간 광무선 통신과 비교하여 수중 가시광 통신기술의 가능성을 제시하고, LED 기반 트랜시버와 CMOS 센서를 통신시스템에 장착하여 수중이미지 전송을 위한 광무선 통신 시스템을 시연하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 D
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• pp.1977-1978
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• 2006

This paper discusses the method of vision based sensor fusion system for biped robot walking. Most researches on biped walking robot have mostly focused on walking algorithm itself. However, developing vision systems for biped walking robot is an important and urgent issue since biped walking robots are ultimately developed not only for researches but to be utilized in real life. In the research, systems for environment recognition and tele-operation have been developed for task assignment and execution of biped robot as well as for human robot interaction (HRI) system. For carrying out certain tasks, an object tracking system using modified optical flow algorithm and obstacle recognition system using enhanced template matching and hierarchical support vector machine algorithm by wireless vision camera are implemented with sensor fusion system using other sensors installed in a biped walking robot. Also systems for robot manipulating and communication with user have been developed for robot.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2009년도 정보 및 제어 심포지움 논문집
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• pp.118-120
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• 2009

In this paper, we present the Q-learning method for adaptive traffic signal control on the basis of multi-agent technology. The structure is composed of sixphase agents and one intersection agent. Wireless communication network provides the possibility of the cooperation of agents. As one kind of reinforcement learning, Q-learning is adopted as the algorithm of the control mechanism, which can acquire optical control strategies from delayed reward; furthermore, we adopt dynamic learning method instead of static method, which is more practical. Simulation result indicates that it is more effective than traditional signal system.

• Journal of Advanced Marine Engineering and Technology
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• 제38권2호
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• pp.169-174
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• 2014

This paper proposes a novel beehive-shaped reflector for application to light-emitting diode (LED) transceivers for illumination and bi-directional visible light communication (VLC). By using a diffuse propagation model extended to line-of-sight and direct signals, the distribution of illuminance and the path loss of the transceiver are investigated to evaluate the performance of the beehive-shaped reflector. To verify bi-directional communication, a VLC-based image capture system, comprising a complementary metal-oxide semiconductor (CMOS) image sensor and video processor unit, is demonstrated. Real-time images captured by the CMOS camera are successfully transmitted to the monitoring system via a free-space channel at a rate of 115.2 kbps.

• 센서학회지
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• 제26권6호
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• pp.408-413
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• 2017

In this paper, we newly developed a byte-inverted transmission method for flicker-free visible light communication (VLC). The VLC transmitter sends original data in the former half period of the clock, and inverted data and in the latter half period of the clock. The VLC receiver receives the original data in the in the former half period of the clock. In this system, we used 480Hz clock that was generated from the 60Hz power line. The average optical power of the LED array in the transmitter is constant, thus flicker-free, in the observation time longer than the period of the clock that is about 2ms. This period is shorter than the maximum flickering time period (MFTP) of 5ms that is generally considered to be safe. This configuration is very useful in constructing indoor wireless sensor networks using LED light because it is flicker-free and does not require additional transmission channel for clock transmission.

• 전기전자학회논문지
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• 제22권4호
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• pp.959-964
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• 2018

본 연구에서는 LED 광시스템과 식물생장제어시스템을 연계하여 센서를 이용하여 식물환경을 제어 가능한 모니터링시스템에 대한 연구이다. 시스템의 성능을 검증하기 위해 에너지효율, data 전송률, 광량제어 특성에 대한 실험을 실시하였다. 실험한 결과 에너지 효율은 80%이상, 무선통신속도가 1Mb/sec이고 광량제어를 5단계이상 조절 가능함으로써 만족한 결과를 얻었다. 제안된 시스템은 LED 식물공장설비에 적용가능하며, 향후 상용화를 위해서는 생산효율 및 노동비 절감을 위한 자동시스템을 구성하여 농업 자동화설비에 기여할 것이다.

• 조명전기설비학회논문지
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• 제22권12호
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• pp.164-175
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• 2008

안개 및 대기의 교란이 광무선 통신에 주는 영향을 해석하기 위해 가시광선영역의 LD(laser diode) 및 적외선 영역의 LD 사용하고, 카세그레인 광학계를 이용하여 광을 송수신하게 하였으며, 광 소신소자로는 APD(avalanch photo diode)를 사용함을 가정하여 대기 중의 안개의 정도에 따른 가시도 및 교란의 세기를 나타내는 굴절률 구조상수에 따른 광 수신 전력, 잡음 전력을 고려한 SNR(signal to noise ratio)을 계산해 보고 각각의 통신 상태에서 BER(bit error rate)이 $10^{-9}$이 가능한 통신 거리를 알아보았다.