• Journal of Positioning, Navigation, and Timing
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• 제12권1호
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• pp.83-89
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• 2023

The Korea Augmentation Satellite System (KASS) system is a Satellite Based Augmentation System (SBAS) under development to provide APV-I SBAS service in the Republic of Korea. The KASS ground segment generates correction and integrity information for GPS measurements of KASS users using the accurate positions of KASS Reference Station (KRS) antenna phase centers. For this reason, the accuracy of KRS reference points through geodetic survey campaigns is one of the important factors for providing the KASS service in compliance with the required navigation performance. In order to obtain accurate positions, two geodetic survey campaigns were performed at several reference points, such as Mark, Center of Mast at Ground Level (CMGL), and Center of Hole in Top Plate (CHTP), of each KRS site using three different survey methods, the Virtual Reference Station (VRS), Flächen Korrektur Parameter (FKP), and raw data post-processing methods. By comparing and analyzing the results, the computed coordinates of the reference points were verified and Antenna Phase Center (APC) positions were calculated using KRS Antenna Reference Point (ARP) data, and the first KASS Site Acceptance Test (SAT#1) was performed successfully using the verified APC coordinates. After the first site survey activities, the KASS operators should maintain the coordinates with the required performance such that the overall KASS navigation performance commitment is guaranteed during the lifetime of 15 years. Therefore, the maintenance plan for the KRS antenna coordinates should be developed before the commissioning of KASS operation planned after 2023. Therefore, this paper presents a geodetic survey method selected for the maintenance activities and provides the rationale for using this method.

• Journal of Communications and Networks
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• 제4권2호
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• pp.148-157
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• 2002

This paper investigates schemes to improve TCP performance in multipath forwarding networks. In multipath routing, packets to the same destination are sent to multiple next-hops in either packet-level or flow-level forwarding mode. Effective bandwidth is increased since we can utilize unused capacity of multiple paths to the destination. In packet-level multipath forwarding networks, TCP performance may not be enhanced due to frequent out-of-order segment arrivals at the receiver because of different delays among paths. To overcome this problem, we propose simple TCP modifications. At the sender, the fast retransmission threshold is adjusted taking the number of paths into consideration. At the receiver, the delayed acknowledgment scheme is modified such that an acknowledgment for an out-of-order segment arrival is delayed in the same way for the in-order one. The number of unnecessary retransmissions and congestion window reductions is diminished, which is verified by extensive simulations. In flow-level multipath forwarding networks, hashing is used at routers to select outgoing link of a packet. Here, we show by simulations that TCP performance is increased in proportion to the number of paths regardless of delay differences.

• Journal of Electrical Engineering and Technology
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• 제5권4호
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• pp.511-521
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• 2010

This paper presents a new algorithm to determine accurate bus-wise transmission loss allocation utilizing path-integrals dictated by the transaction strategy. For any transaction strategy, the total sum of the allocated transmission losses of all buses is equal to the actual loss given by the AC power-flow calculation considering the distributed slack. In this paper, the bus-wise allocation of the transmission loss is calculated by integrating the differential loss along a path determined by the transaction strategy. The proposed algorithm is also compared with Galiana's method, which is the well-known transmission loss allocation algorithm based on integration. The performance of the proposed algorithm is evaluated by case studies carried out on the WSCC 9-bus, IEEE 14-bus, New England 39-bus, and IEEE 118-bus systems. The simulation results show that the proposed algorithm is fast and accurate with a large step size.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권8호
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• pp.2751-2771
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• 2022

In the post covid-19 era, organizations will experience a new environment. Advances in technologies such as AI and big data, and new experiences such as online meetings and lectures, will increase the use of online communication. Businesses will increasingly engage in online-based information sharing, virtual team operations, and online meetings. This study focuses on meeting climate and satisfaction, to improve the performance of online meetings. Existing studies on meeting climate presuppose off-line situations. Offline and online communication methods and meeting formats are different. This paper proposes new climate types to develop an appropriate climate for online-based meetings. To apply these climates in online meetings, a measurement scale was developed and the impact on online meeting satisfaction was verified. As a result of the study, it was found that the creativity-oriented meeting climate was the most important, and relation-oriented and participation-oriented meeting climates also had a significant effect, while the direction-oriented and task-oriented climates were relatively less important. This study develops new variables and measurements for online meeting climates, and explains their importance. Companies will be able to leverage the appropriate climates for online meetings to improve performance.

• 한국정보전자통신기술학회논문지
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• 제13권5호
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• pp.443-451
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• 2020

하이퍼루프는 튜브 내를 부상한 상태로 초고속주행하는 미래형 이동 시스템으로 제안되었다. 하이퍼루프에서 달리는 포드 차량은 선형 동기모터 상에서 주행하기에 위치측정이 근본적 중요성을 가진다. 1000km/h 이상의 속도로 주행하는 포드 차량의 가속과 감속에 정밀한 위치측정이 요구되며 또한 차량간 거리 유지를 위한 속도 조절에도 요구된다. 본 논문은 laser surface velocimeter를 개량하여 새로운 범위조건의 위치측정을 시도한다. 높은 정밀도로 초고속 이동체의 위치를 측정해야 하기에 지나가는 타일의 레이저 반사율 차이 검출로 변위를 계산하는 상대위치 측정장치를 구현하여 성능시험으로 평가하였다. 500km/h 미만의 포드 속도에서 cm 단위의 정밀도로 정확한 위치 측정을 보였으며, 500km/h 이상의 포드 속도에서도 0.1% 미만의 매우 낮은 오차율로 위치측정 결과를 보여주었다. 향후 500km/h 이상에서의 오차율도 0에 수렴하도록 연구를 진행해야 한다.

• 한국산학기술학회논문지
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• 제18권2호
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• pp.704-710
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• 2017

본 연구팀은 프레스 공정의 협소공간에서 작업이 가능한 6자유도 로봇을 개발하고 있으며, 본 논문은 개발된 로봇의 작업 시간을 최소화하기 위한 작업 시퀀스 최적화 방법을 제안하였다. 우선 6 자유도 로봇의 기구학을 모델링하고 작업 시간 예측 방법을 기술하였다. 그리고 작업 시퀀스 최적화를 위하여 수학적 모델을 제시하고, 이를 바탕으로 개미 집단 시스템(ant colony system), 시뮬레이트 어니일링(simulated annealing), 유전자 알고리즘(genetic algorithm)의 세 가지 최적화 방법을 적용하고 결과를 비교 분석하였다. 시뮬레이션 결과 유전자 알고리즘이 가장 좋은 결과를 보임을 확인할 수 있었으며, 계산 속도 측면에서도 가장 빨리 최적값에 수렴하였다. 또한, 개미집단시스템과 시뮬레이티드 어니일링의 경우 여러 파라미터 값들의 설정에 따라 수렴된 최적값의 편차가 비교적 큰 것에 비하여, 유전자 알고리즘은 파라미터 값에 상관없이 안정적으로 근사 최적값을 찾을 수 있었다. 마지막으로, 로봇의 작업시퀀스 최적화 방법을 시각적으로 검증하기 위하여 Mathworks 사의 Matlab과 Coppelia Robotics 사의 V-REP (virtual robot experimentation platform)를 사용한 시뮬레이션을 수행하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권5호
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• pp.1554-1566
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• 2014

Cloud Computing allows application providers seamlessly scaling their services and enables users scaling their usage according to their needs. In this paper, using queuing game model, we present service scheduling schemes which are used in software as a service (SaaS). The object is maximizing the Cloud Computing platform's (CCP's) payoff via controlling the service requests whether to join or balk, and controlling the value of CCP's admission fee. Firstly, we treat the CCP as one virtual machine (VM) and analyze the optimal queue length with a fixed admission fee distribution. If the position number of a new service request is bigger than the optimal queue length, it balks. Otherwise, it joins in. Under this scheme, the CCP's payoff can be maximized. Secondly, we extend this achievement to the multiple VMs situation. A big difference between single VM and multiple VMs is that the latter one needs to decide which VM the service requests turn to for service. We use a corresponding algorithm solve it. Simulation results demonstrate the good performance of our schemes.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2019년도 추계학술발표대회
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• pp.491-494
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• 2019

The results from the analysis of recent security breach cases of industrial control systems revealed that most of them were caused by the employees of a partner company who had been managing the control system. For this reason, the majority of the current company security management systems have been developed focusing on their performances. Despite such effort, many hacking attempts against a major company, public institution or financial institution are still attempted by the partner company or outsourced employees. Thus, the institutions or organizations that manage Industrial Control Systems (ICSs) associated with major national infrastructures involving traffic, water resources, energy, etc. are putting emphasis on their security management as the role of those partners is increasingly becoming important as outsourcing security task has become a common practice. However, in reality, it is also a fact that this is the point where security is most vulnerable and various security management plans have been continuously studied and proposed. A system that enhances the security level of a partner company with a Virtual Desktop Infrastructure (VDI) has been developed in this study through research on the past performances of partner companies stationed at various types of industrial control infrastructures and its performance outcomes were statistically compiled to propose an appropriate model for the current ICSs by comparing vulnerabilities, measures taken and their results before and after adopting the VDI.

• 한국항행학회논문지
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• 제25권5호
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• pp.384-389
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• 2021

네트워크 기반 무인기 제어통신 시스템을 위한 복잡도와 성능을 고려한 지상국 최적 안테나 패턴 설계 방식을 제시하였다. 다수개의 측면 섹터와 한 개의 상향 섹터로 구성되는 지상국 안테나의 섹터 수, 수평/수직 빔폭, 틸팅각도 등 안테나 설계 파라미터의 변화에 따른 수직/수평 각도 별 안테나 이득을 모델링하고, 가상의 3차원 공간 내에서 각 파라미터의 변화가 신호 대 잡음 비 (SNR : signal to noise ratio) 분포에 미치는 영향을 분석하였다. 다양한 파라미터 중 측면 섹터의 틸팅 각도가 성능에 가장 큰 영향을 미치는데, 지상국 간 거리가 길수록, 최고 고도가 높을수록, 측면 섹터 수가 작을수록 틸팅 각도를 낮춰야 함을 확인할 수 있었다. 또한 최저 SNR 최대화 측면에서는 측면 섹터 수직 빔폭을 늘리는 것이 유리하지만 평균 SNR 측면에서는 수직 빔폭을 줄이는 것이 유리함을 확인하였다.

• 한국지반공학회논문집
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• 제36권10호
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• pp.41-56
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• 2020

지진 경보 시스템이 빠르고 정확하게 가동하기 위해서는 충분한 수량의 계측 시스템 확보와 더불어서 적절한 계측 데이터 해석기술 개발이 요구된다. 신규 지진계를 설치시 많은 비용이 소모되기 때문에, 열차 내 가속도계 등을 대체재로 지진 경보 시스템에 활용하는 것이 효율적이다. 그러나 열차에 설치된 가속도계의 경우, 지진계와는 달리 열차 주행시 진동 데이터가 포함되어 있다. 또한, 지진 발생시 성토구간에 의해서 변화된 지진응답을 계측하게 된다. 본 연구에서는 위의 특성들이 포함된 열차 가속도계 데이터에 기반한 지진감지 기술을 제안하고자 한다. 우선, 성토구간의 지진응답 해석기법을 활용하여 열차가 성토구간을 지날 때 지진이 발생하는 것을 구현한 가상의 열차 가속도 데이터를 구축하였다. 구축한 가속도 데이터를 Short time Fourier Transform(STFT)와 Wavelet Transform(WT)을 활용하여 시간-주파수 분석을 수행하였다. 분석 결과, STFT가 장주기 지진 감지에 적합한 반면, WT의 경우 단주기 지진 감지에 유용함을 확인하였다.