• Journal of Korean Society of Transportation
• /
• v.23 no.1
• /
• pp.93-102
• /
• 2005

An Origin-Destination (O/D) is considered as one of the important information in route choices and trip assignments. A household interview survey is deemed to be the traditional and the most widely used method in making sample O/D and its conversion to the total O/D. Some researchers have studied to estimate dynamic O/D from the relationship between link volumes and trip assignment model. Nowadays, owing to the recent rapid spread of cellular phones. Location information of the cellular phone through the Base Station(BS) is considered as an alternative to O/D estimation. In this study, the methodology of generating BS-based O/D and the methodology of converting this O/D into an administrative district-based O/D are proposed. The information of GPS positions and cellular BS positions have acquired by establishing GPS equipment and cellular phone on taxies in Cheongju. Three weeks data are collected and used in estimating O/D by matching them on a digital map. Scatter diagram and sample correlation coefficients are used to investigate the similarity of the GPS-based O/D pattern among weeks, among days, and among times in day. The results show that there are few significant differences among weeks. But there is a difference in O/C pattern between weekday and weekend. Furthermore, there is a difference between morning peak and afternoon peak. Two methodologies are proposed to convert BS-based O/D into an administrative district-based O/D. The first one is to use the distribution pattern of GPS coordinates, the other is to use the coverage area of the BSs. To validate such converted O/D, GPS O/D is used as a true value. The statical analyses through scatter diagram, MAE and RMSE shows that there is few significant defference of pattern between the estimated BS-based O/D and GPS O/D. In the case of using only cellular information, the methodology using coverage area of the BSs is recommended for estimating O/D.

• Journal of KIISE
• /
• v.44 no.8
• /
• pp.854-859
• /
• 2017

Caching popular videos in the storage of base stations is an efficient method to reduce the transmission latency. This paper proposes an incentive proactive cache mechanism in the wireless network to motivate the content providers (CPs) to participate in the caching procedure. The system consists of one/many Infrastructure Provider (InP) and many CPs. The InP aims to define the price it charges the CPs to maximize its revenue while the CPs compete to determine the number of files they cache at the InP's base stations (BSs). We conceive this system within the framework of Stackelberg game where InP is considered as the leader and CPs are the followers. By using backward induction, we show closed form of the amount of cache space that each CP renting on each base station and then solve the optimization problem to calculate the price that InP leases each CP. This is different from the existing works in that we consider the non-uniform pricing scheme. The numerical results show that InP's profit in the proposed scheme is higher than in the uniform pricing.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.37A no.9
• /
• pp.762-771
• /
• 2012

In this paper, we propose an adaptive power control scheme employing a self-optimization concept in femtocell systems, in order to improve system capacity, thereby reducing call-drop probability. In the proposed scheme, each femto base station(FBS) controls individual channel's transmission power base on two parameters; the neighboring cell's transmission power for each individual channel which is delivered from a femto-gateway and the received power strength from neighboring cells which is periodically measured by means of a spectrum sensing. Adaptive adjustment of individual channel's transmission power in accordance with femto mobile station(FMS) mobility features can also reduce undesirable handovers and evenly distribute traffic load over all femtocells. In addition, the manipulative control of channel's transmission power is able to keep the system coverage and the call-drop probability within an acceptable range, regardless of density of femtocells. Computer simulation shows that the proposed scheme outperforms existing schemes in terms of the system coverage and the call-drop probability.

• Journal of Digital Convergence
• /
• v.17 no.12
• /
• pp.197-202
• /
• 2019

In line with the era of the 4th Industrial Revolution, 5G technology has become common technology, and 5G technology is evaluated as a technology that minimizes the speed and response speed compared to 4G using technologies such as network slicing and ultra-multiple access. 5G NR stands for 5G mobile communication standard, and network slicing cuts the network into parallel connections to optimize the network. In addition, the risk of hacking is increasing as data is processed in the base station unit. In addition, since the number of accessible devices per unit area increases exponentially, there is a possibility of base station attack after hacking a large number of devices in the unit area. To solve this problem, this study proposes the introduction of quantum cryptography and 5G security standardization.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.23 no.1
• /
• pp.1-19
• /
• 2018

In order to compare significant wave height (SWH) data from multi-satellites (GFO, Jason-1, Envisat, Jason-2, Cryosat-2, SARAL) and SWH measurements from Ieodo Ocean Research Station (IORS), we constructed a 12 year matchup database between satellite and IORS measurements from December 2004 to May 2016. The satellite SWH showed a root mean square error (RMSE) of about 0.34 m and a positive bias of 0.17 m with respect to the IORS wave height. The satellite data and IORS wave height data did not show any specific seasonal variations or interannual variability, which confirmed the consistency of satellite data. The effect of the wind field on the difference of the SWH data between satellite and IORS was investigated. As a result, a similar result was observed in which a positive biases of about 0.17 m occurred on all satellites. In order to understand the effects of topography and the influence of the construction structures of IORS on the SWH differences, we investigated the directional dependency of differences of wave height, however, no statistically significant characteristics of the differences were revealed. As a result of analyzing the characteristics of the error as a function of the distance between the satellite and the IORS, the biases are almost constant about 0.14 m regardless of the distance. By contrast, the amplitude of the SWH differences, the maximum value minus the minimum value at a given distance range, was found to increase linearly as the distance was increased. On the other hand, as a result of the accuracy evaluation of the satellite SWH from the Donghae marine meteorological buoy of Korea Meteorological Administration, the satellite SWH presented a relatively small RMSE of about 0.27 m and no specific characteristics of bias such as the validation results at IORS. In this paper, we propose a conversion formula to correct the significant wave data of IORS with the satellite SWH data. In addition, this study emphasizes that the reliability of data should be prioritized to be extensively utilized and presents specific methods and strategies in order to upgrade the IORS as an international world-wide marine observation site.

• Journal of the Korean housing association
• /
• v.16 no.5
• /
• pp.49-56
• /
• 2005

This study will focus on status and structure of Japanese public reverse mortgage that has been changed since 1980. Especially, on newly introduced long-term supporting system for living fund after 2003. Private housing construction companies studied preceding cases of real estate products with reverse mortgage theory and also induced learning point from the change of Japanese public reverse mortgage market. From this on the purpose of this study is suggesting a better plan for successful reverse mortgage introduction in Korea. The data and articles of Japanese reverse mortgage are used for this study, also reverse mortgage related data are collected from web-site and research reports from the inside and outside of the country. From the total postal survey in September, 2004, the system contents after Year 2003 are described here. As described above, reverse mortgage is a way to support public social pension system and expected to play an important role as an assisting method for stable housing and supporting living cost to the aged. Eventually, it is necessary to find a way for introducing a public reverse mortgage as a welfare system for low income people.

• Journal of Welding and Joining
• /
• v.13 no.3
• /
• pp.18-33
• /
• 1995

천연가스는 지구상에서 비교적 광범위하게 생산되며 구미 등에서는 대부분 pipe line으로 소비지까지 운송하여 사용하고 있지만 일본 등에서는 액화 천연가스 (LNG)로 저장, 수송하여 사용하고 있다. LNG 저장탱크는 생산측의 액화기지와 사용측 의 수입기지에 설치되며 지금까지 약 240기가 건설되어 있다. 종래 탱크 1기의 용량 은 대부분 6 - 8만m$^{3}$ 규모였지만, 토지의 유효이용 등으로 대형화되고 있으며, 또 지상식에서는 PC(Prestressed Concrete)의 방파제를 외부탱크에 근접시켜 외부탱크 와 일체화시킨 PC LNG 탱크가 개발.설계되었다. 일본에서는 이미 이 방식으로 세계 최대규모인 14만m$^{3}$ 탱크가 건조되어 가동 중이다. LNG의 주성분은 메탄이고 비등점은 -161.5.deg.C로 극저온이다. 이러한 저온에서도 취화되지 않고 사용할 수 있는 재료는 9%Ni강, Al 합금, 스테인레스강 및 Invar 등이 있지만, 탱크의 대형화에 따라 가공성, 용접성 및 경제성을 고려하여 요즈음은 9%Ni강이 주로 사용되고 있다. 한편 9%Ni강용 용접재료는 고Ni계 합금 및 모재와 동일한 성분계의 공금계가 있지만 지금까지 고 Ni계 합급이 주로 사용되고 있다. 본 내용에서는 9%Ni강을 사용한 지상식 평지원통형 LNG 탱크를 예로 들어 탱크의 개요 및 용접재료, 용접시공 등을 포함한 용접기술에 대해서 개괄적으로 설명하고자 한다.

• Water for future
• /
• v.17 no.4
• /
• pp.303-310
• /
• 1984

One of the delicate problems in aquifer problems in aquifer management is the identification of the spatial distribution of the hydrological parameters. To determine the distribution of the transmissivity in a aquifer, several data are available; the local values of transmissivity around well, interference tests, some knowledge of geological structure. All this information has to be combined to find a plausible representation of the aquifer. According to a three phased optimization process calculation is carried out; geostatistical estimate of the parameter field on the basis of known well point values adjustable on a limited numerical model, and modification of the values ot pilot points by a minimization algorithm. This procedure, applied to a known case, has proved to be very useful.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
• /
• 1993.11a
• /
• pp.57-63
• /
• 1993

냉열발전기술은 일본에서 많이 연구되어 다수의 상업 플랜트가 가동되고 있다. 일본에서는 천연가스 공급압력의 이원화(40 kgf/$\textrm{cm}^2$, 10 kgf/$\textrm{cm}^2$)로 직접 팽창방식을 적용할 수 있어 냉열발전의 경제성이 유리한 반면 국내에서는 비교적 높은 압력(70kgf/$\textrm{cm}^2$)의 단일 압력 공급체계에 적합한 냉열발전 시스템을 모색하여야 한다. 특히 발전용량 규모가 비교적 적은 냉열발전 시스템의 경제성 측면의 불리한 점을 고려할 때 적용 가능한 해당 발전공정들에 대해 전산모사의 방법을 이용하여 다양한 설계조건에서 최적의 조건들을 검토하여야 한다. 따라서 본 연구에서는 LNG의 저온 Exergy를 이용한 Rankine Cycle, LNG의 압력 Exergy를 이용한 부분팽창 Cycle 및 이 두 싸이클의 혼합 공정인 Linde 공정에 대해 현재 인수기지에서 운영되고있는 각종 설비들의 설계 데이타를 기준으로 상용모사기인 ASPEN PLUS를 이용, 국내 천연가스 공급 체계에 의거 각 공정별 최대 및 최적의 전력 발생 조건들을 검토하였다. 공정별 출력 및 엑서지 효율을 비교한 결과 약 3 ~ 6 Mw의 전력을 생산할 수 있음을 알 수 있었으며 최대 엑서지 효율은 37 %를 얻을 수 있었다. 또한 부분직접팽창방식의 최적시스템을 제시하였고 동일한 전열면적인 경우 부분직접팽창과 랭킨 싸이클의 성능은 비슷한 것으로 확인되었다.

• Journal of Korean Society for Geospatial Information Science
• /
• v.23 no.4
• /
• pp.67-74
• /
• 2015

GNSS/Leveling technology makes it possible to get geoidal height geometrically using GNSS and Leveling technology. GNSS/Geoid technology refers to a technology for obtaining orthometric height by subtracting geoidal height achieved by Geoid technology from ellipsoidal height achieved by GNSS technology. The purpose of this study is to verify the accuracy of the ellipsoidal height determination in order to verify the accuracy of the orthometric height determination by the GNSS/Geoid technology. For the study, a test bed was selected in Kyungnam province and GNSS Static surveying was accomplished in the test bed and then the GNSS data was processed in accordance with various analysis conditions. So, it was verified the accuracy of the ellipsoidal heights determination in accordance with the surveying conditions under the GNSS Static surveying. According to the research results, to ensure the 3cm goal accuracy of the ellipsoidal height determination, it should be surveyed by four fixed points on the survey area periphery and more than two hours of the GNSS occupation time, And also, it was found that should be limited to a baseline distance of 20km under the GNSS Static surveying.