• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.23 no.5
• /
• pp.131-138
• /
• 2023

In this paper, a free space optical communication device that can be used in a mobile base station of several km or less was fabricated and its characteristics were investigated. To overcome the loss due to atmospheric transmission, an optical fiber amplifier (EDFA) with an output of 23 dBm or more was used. In order to increase the focusing speed and miniaturization of the laser beam, an optical lens was manufactured, and a transmission lens was designed to have beam divergence within the range of 1.5 to 1.8 [mrad]. A PT module that controls PAN/TILT was fabricated in order to reduce pointing errors and effective automatic alignment between transceiver devices. In this study, Reed-Solomon (RS) code was used to maintain the transmission quality above a certain level. It was manufactured to be able to communicate at a wireless distance of 300m in a weather situation with visibility of 300m. For performance measurement, it was measured using BERT and eye pattern analyzer, and it was confirmed that BER can be maintained at 2.5Gbps.

• Journal of the Korea Society of Computer and Information
• /
• v.29 no.3
• /
• pp.1-10
• /
• 2024

The research on predicting the routes of ships, which constitute the majority of maritime transportation, can detect potential hazards at sea in advance and prevent accidents. Unlike roads, there is no distinct signal system at sea, and traffic management is challenging, making ship route prediction essential for maritime safety. However, the time intervals of the ship route datasets are irregular due to communication disruptions. This study presents a method to adjust the time intervals of data using appropriate interpolation techniques for ship route prediction. Additionally, a deep learning model for predicting ship routes has been developed. This model is an LSTM model that predicts the future GPS coordinates of ships by understanding their movement patterns through real-time route information contained in AIS data. This paper presents a data preprocessing method using linear interpolation and a suitable deep learning model for ship route prediction. The experimental results demonstrate the effectiveness of the proposed method with an MSE of 0.0131 and an Accuracy of 0.9467.

• The Korean Journal of Quaternary Research
• /
• v.32 no.1_2
• /
• pp.51-66
• /
• 2018

Climate change and large-scale human interference increase flow instability due to changes in watershed flow and sediment transport patterns. There are local problems in solving problems related to sediments, namely the existence of specific problems at specific sites or areas, and the resolution of these problems is limited to short-term and regional, resulting in other temporal and spatial influences and impacts. Therefore, this study intends to introduce and propose a conceptual framework for comprehensive sediment management in terms of watershed scale for solving problems related to sediments in watersheds. In the watershed scale, comprehensive sediment management should be done, to do this, a comprehensive understanding of the movements of sediments accompanied by cooperation with science-policy-operation-residents should be given priority.

• Journal of KIISE:Information Networking
• /
• v.29 no.6
• /
• pp.595-612
• /
• 2002

One of the most important issues in guaranteeing the high degree of QoS on mobile computing is how to reduce hand-off drops caused by lack of available bandwidth in a new cell. Each cell can request bandwidth reservation to its adjacent cells for hand-off calls. This reserved bandwidth can be used only for hand-offs, not for new calls. It is also important to determine how much of bandwidth should be reserved for hand-off calls because reserving too much would increase the probability of a new call being blocked. Therefore, it is essential to develop a new mechanism to provide QoS guarantee on a mobile computing environment by reserving an appropriate amount of bandwidth and call admission control. In this paper. bandwidth reservation and call admission control mechanisms are proposed to guarantee a consistent QoS for multimedia traffics on a mobile computing environment. For an appropriate bandwidth reservation, we propose an adaptive bandwidth reservation mechanism based on an MPP and a 2-tier cell structure. The former is used to predict a next move of the client while the latter to apply our mechanism only to the client with a high hand-off probability. We also propose a call admission control that performs call admission test only on PNC(Predicted Next Cell) of a client and its current cell. In order to minimize a waste of bandwidth caused by an erroneous prediction of client's location, we utilize a common pool and QoS adaptation scheme. In order evaluate the performance of our call admission control mechanism, we measure the metrics such as the blocking probability of new calls, dropping probability of hand-off calls, and bandwidth utilization. The simulation results show that the performance of our mechanism is superior to that of the existing mechanisms such as NR-CAT2, FR-CAT2, and AR-CAT2.

• Korea journal of population studies
• /
• v.10 no.2
• /
• pp.17-45
• /
• 1987

This study contributes to understanding women's labor market behavior by focusing on a particular set of labor force transitions - labor force withdrawal and entry during the period surrounding the first birth of a child. In particular, this study provides a dynamic analyses, using longitudinal data and event history analysis, to conceptualize labor force behaviors in a straightforward way. The main research question addresses which factors increase or decrease the hazard rates of leaving and entering the labor market. This study used piecewise Gompertz model, following the guide of the non-parametric analysis on the hazard rates, which allowed relatively detailed description on the distribution of timing of leave and entry to the labor market as parameters of interest. The results show that preferences and structural variables, as well as economic considerations, are very important factors to explain the labor market behavior of women in the period surrounding childbirth.

• Journal of the Korean earth science society
• /
• v.41 no.6
• /
• pp.557-574
• /
• 2020

The purpose of this study is to analyze the cause of high PM2.5 mass concentrations in Cheongju for the period of non-Asian dust days using the weather chart, the stream lines at 850 hPa, the backward trajectory, and the weather and air quality model. As a result of analyzing the time series of PM2.5 concentrations and weather charts for the episodic days in Cheongju, the weather patterns were shown in related to long-range transport of PM2.5 from China or surrounding areas. In fact, in the PM2.5 time series, 60-80 ㎍ m-3, which is more than 2-3 times higher than the concentration attributed to Cheongju activities, was observed as a background concentration related to long-range transport. The distribution of high PM2.5 concentration was typically dependent on the locations of the high and low pressures above the ground while the upper jet stream passed through the Korean Peninsula. Consequently, the high PM2.5 concentration in Cheongju is due to massive air pollutants in the form of smog originated from industrial, household and energy combustion sources of Beijing and other nearby regions of China. These air pollutants move along a fast zonal wind caused by the atmospheric pressure arrangement. high concentration of PM2.5 in Cheongju City is because the mass of air pollutants in the form of smog generated from industrial, household and energy combustion origins in Beijing or other nearby regions of China move along a fast wind speed zone according to the atmospheric pressure arrangement of long-distance transportation. Air pollutants including PM2.5 show an M-shaped pattern that passes through the topography of the Cheongju basin from north to south as a belt or band-shaped pollutant. The ground high pressure according to the above-ground high pressure expansion area and cut-off low or low pressure arrangement, or the bands in the form of river stems appear in a gradual incremental pattern that changes into a U-shape under the influence of the wind.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.18 no.7
• /
• pp.1044-1049
• /
• 1993

In this paper, it is shown that B-CDMA systems inherently reduce the effects of Multi Path fading phenomena which causes to degrade the performance of mobile communication systems. B-COMA systems use PN codes of high chip rates ( > 10 Mbps) and evaluate autocorrelation with the same code in the receiver. Therefore, it is possible that multipath signals, whose delay time is longer than one chip duration compared to the first signal, are removed. We model the wideband fading channel as a suitable linear filter, and perform computer simulation of signal transmission and reception. Graphic comparison of eye diagrams between the narrowband and wideband systems is shown.

• Korean Journal of Materials Research
• /
• v.6 no.1
• /
• pp.106-115
• /
• 1996

본 연구에서는 PET(PentaEthoxy Tanatalum:Ta(OC2H5)5) 유기금속 화합물 전구체를 사용하여 차세대 초고집적회로 제조시 고유전체 물질로 유망한 Ta2O5 박막을 열화학증착 방법에 의하여 증착하였다. 본 증착실험을 통하여 여러 가지 운속기체, 기판온도, 반응압력 등의 공정변수가 층덮힘에 미치는 영향을 고찰하였으며 Monte Carlo 전산모사 결과와 기판온도 변화에 따른 층덮힘 패턴의 변화에 대한 실험결과를 비교하여 부착계수를 산출하였다. 운송기체로는 N2, Ar, He을 바꿔가며 실험하였으며 He>N2>Artns으로 층덮힘이 양호한 것으로 나타났다. 이는 운송기체의 종류에 따라 운동량 확산도, 열 확산도, 물질 확산도 등의 이동현상 특성값들이 다르기 때문이라 생각된다. 기판온도의 증가는 운송기체의 종류에 관계없이 층덮힘을 악화시켰으며 도랑내부에서의 Knudsen 확산과 표면반응물의 탈착에 비해 표면반응이 보다 지배적인 역할을 담당함을 알 수 있었다. 또한 질소를 운송기체로 사용한 경우에 부착계수의 겉보기 활성화 에너지는 15.9Kcal/mol로 나타났다. 그리고 3Torr 이하에서 반응압력이 증가하는 반응압력이 증가하는 경우에는 물질 확산도의 감소 효과 때문에 층덮힘이 악화되었다. 본 연구결과 3Torr, 35$0^{\circ}C$에서 He 운송기체를 이용한 경우가 가장 우수한 층덮힘을 얻을 수 있는 최적 공정 조건임을 알 수 있었다.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.13 no.3
• /
• pp.25-31
• /
• 2013

The AVC System which has operated in Highways has two-piezo sensors. In this system the piezo sensors are installed on parally each other this configuration has a defect about diversion driving and sensor damage. In this reserch, 3-Sensor AVC algorithm has been proposed which is supported enhance accuracy of the vehicle classification rate compare with usual 2-Sensor systems. This algorithm is allowed to calculate wheel tread, wheel width. The third inclinded piezo sensor can detec twheel tread, wheel width using signal processing. 3-Sensor AVC has been installed in real highway and the outcome performance has been proof.

• 한국HCI학회:학술대회논문집
• /
• 2006.02a
• /
• pp.672-677
• /
• 2006

유비쿼터스 컴퓨팅 환경에서 상황 인지 서비스 제공을 위한 프레임워크들은 환경에 있는 응용 서비스들로 하여금 사용자 행동 패턴을 지속적으로 모니터링하며, 하나의 중앙집중식 서버에서 축적된 사용자 프로파일을 관리하도록 개발되어 왔다. 그러나, 전체 환경이 사용자 개개인의 서비스에 대한 요구 및 선호도를 파악하고 관리하는 일은 비효율적이다. 그리하여, 사용자 프로파일 관리 서버를 사용하지 않고 개인화된 서비스를 제공하기 위하여 휴대용 정보 단말기가 직접 사용자의 서비스에 대한 선호도를 인식하고 관리하는 사용자 프로파일 관리 프레임워크를 제안한다. 스마트 홈 환경의 이동형 사용자의 컨텍스트 인식을 위해서는 사용자 몸에 부착되어 있는 센서들이 사용자에 대한 정보를 휴대용 정보 단말기로 전달하며, 각 정보 단말기는 다양한 센서들로부터 획득한 정보와 정보단말기를 통해 제공되는 사용자의 직접적인 요구정보를 서비스 목적에 맞게 재해석하여 사용자 선호도에 맞는 서비스 내용을 제공하도록 하는 것이다. 제안된 프레임워크는 휴대용 정보 단말기를 통해 사용자와 환경과의 상호작용을 필요로 하는 유비쿼터스 기술이 활용 가능한 다양한 어플리케이션에 광범위하게 활용될 수 있다. 더 나아가, 사용자의 사적인 정보 보호를 보장하면서 개인화된 서비스 제공을 가능하게 할 수 있다.