• KIPS Transactions on Computer and Communication Systems
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• v.9 no.4
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• pp.83-88
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• 2020

In Solar-powered wireless sensor networks(SP-WSN), the battery is periodically charged, so the best use of harvested energy is more important, rather than minimizing energy consumption. Meanwhile, as is well known, the reliability of communication between sensor nodes is very limited due to the resource-constraint of sensor nodes. In this paper, we propose an advanced FEC (forward error correction) scheme which can give SP-WSN more reliability for communication. Firstly, the proposed scheme uses energy modeling to calculate the amount of surplus energy which can be utilized for extra operations, and then determines the number of additional parity bits according to this amount of surplus energy. At the same time, link quality modeling calculates the optimal parity bits for error recovery in the current data communication environment. Finally, by considering these two parity sizes, it is possible to determine the optimal parity size that can maximize the data reliability without affecting the node black out. Performance verification was performed by comparing the amount of data collected at the sink and the number of outage nodes with other schemes.

• Journal of KIISE:Computing Practices and Letters
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• v.16 no.5
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• pp.556-560
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• 2010

In the wireless sensor networks using a multi-hop, quality variation of links occurs irregularly due to the hardware restriction and environmental factor. If an appropriate route, which is affected by the quality variation, is not selected. Traditionally, a beacon is periodically broadcasted and the link quality is estimated. However, the periodically beacon based scheme cannot efficiently estimate the quality of the link changing irregularly. In this paper, a scheme to estimate the link quality adaptively according to network state is proposed. When the link quality changes, the scheme adapts to a change agilely and packet losses are reduced. When there is no change of the link quality, the link quality is estimated in the long period and the energy consumption is reduced. Through performance evaluations, we prove that our adaptive link estimation scheme improves the energy efficiency and packet reception ratio than the periodic estimation scheme.

• Journal of KIISE:Computing Practices and Letters
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• v.16 no.11
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• pp.1081-1085
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• 2010

In the wireless sensor networks, power consumption and interference among the nodes can be reduced by using the transmission power control. Because link quality is changed by spatial and temporal effect, link failures are frequently occurred. In order to adapt to link quality variation, existing transmission power control schemes broadcast beacon messages periodically to neighbor nodes and control the transmission power dynamically. However, it can effect on the time and energy overhead according to period of transmission power control. In this paper, the dynamic method of transmission power control by the link quality variation and variable period are proposed. When a link quality is unstable, the control duty cycle is reduced and the link quality is agilely maintained. In contrast, when link quality is stable, the control period is increased and control overhead is decreased.

• Journal of Internet Computing and Services
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• v.8 no.5
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• pp.21-33
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• 2007

An overlay network is a virtual network which is constructed on top of a physical computer network. A node in the overlay network is connected through virtual or logical links, where each link corresponds to a path of the links in the underlying physical network. Overlay networks are suitable for sharing heterogeneous resources in distributed environments, However, overlay networks are limited for achieving reliable communication that failure detection in overlay networks is a very important issue. In this paper, we review conditions of conventional failure detection and propose a new approach to failure detection and resilience which can be applied to HRing (Hierarchical Ring) overlay networks. The proposed method consists of the failure detection and the failure resilience phases. Because it utilizes the characteristics of the HRing overlay network for failure detection, it can reduce unnecessary network traffic and provide better scalability and flexibility. We also analyzed and evaluated the performance of the proposed approach through simulations.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.6
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• pp.537-546
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• 2010

This research work contributed to a study for the procedure and methodology to assess the fatigue durability for a composite torque link of helicopter landing gear, which was newly developed and fabricated by the resin transfer moulding technique to interchange with metal component. The simulated load spectrum anticipated to be applied to the torque link during its operation life was generated using an advanced method of probabilistic random process, and the fatigue durability was evaluated by the strength degradation approach on the basis of material test data. The full scale fatigue test was also performed and compared with the analysis results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.9A
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• pp.844-855
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• 2006

The communication system using multiple antennas improves link reliability or system capacity using tx & rx diversity, spatial multiplexing, and beamforming technique with services and characteristics of channel environment. This system is sensitive to spatial channel environment. In case of diversity, the lower correlation among links as a LoS environment, the better performance is acquired. In practical channel environment, However, there is high correlation, and there is high performance difference between ideal case and practical case. On the contrary, in case of beamforming, the higher correlation among links, the better performance is acquired. If we use the spatial adaptive transmission technique with spatial channel characteristics, we can get the system that maintains minimum link reliability and guarantees the overall system performance. In this paper, we propose the adaptive transmission and reception technique which use diversity or beamforming technique with channel characteristics.

• Journal of Korean Society of Transportation
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• v.27 no.1
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• pp.117-127
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• 2009

This study analyzed the uncertainty of the forecasted link traffic flow, and estimated of the interval link flow using Korea Transport Data Base (KTDB) to consider those risks into the feasibility study. In the paper, the uncertainty was analyzed according to the stochastic variation of the KTDB origin-destination traffic. It was found that the uncertainty of the entire network traffic forecasts was 15.4% in average,. when the stochastic variation of the KTDB was considered. The results showed that the more congested the roads were, the bigger the uncertainty of forecasted link traffic flow were found. In particular, we estimated the variance of the forecasted traffic flow, and suggested interval estimates of the forecasted traffic flow instead of point estimates which were presented in the common feasibility studies. These results are expected to contribute the quantitative evaluation of uncertain road investment projects and to provide valuable information to the decision makers for the transport investment.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.3
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• pp.422-429
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• 2022

In this paper, the intermediate frequency transmission signal level between the network system-based baseband and RF unit consisting of multi-channel airborne relay devices and a lot of mission devices, which are currently undergoing technology development tasks, is kept constant at the reference signal level. Considering the other party's receiving input range, despite changes in the short-range long-range wireless communication environment, it presents a multi-link protection and MLP-A algorithm that allows signals to be transmitted stably and reliably through signal detection automatic gain control, and experiments and analysis considering short-distance and long-distance wireless environments were performed by designing, manufacturing, and implementing RF units to which MLP-A algorithms were applied, and applying distance calculation equations to the configuration of multiple air movements and verification networks. Through this, it was confirmed that a stable and reliable RF communication system can be operated.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.19 no.5
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• pp.70-81
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• 2020

Point-by-point data, which is abundantly collected by vehicles with embedded GPS (Global Positioning System), generate useful information. These data facilitate decisions by transportation jurisdictions, and private vendors can monitor and investigate micro-scale driver behavior, traffic flow, and roadway movements. The information is applied to develop app-based route guidance and business models. Of these, speed data play a vital role in developing key parameters and applying agent-based information and services. Nevertheless, link speed values require different levels of physical storage and fidelity, depending on both collecting and reporting intervals. Given these circumstances, this study aimed to establish an appropriate collection interval to efficiently utilize Space Mean Speed information by vehicles with embedded GPS. We conducted a comparison of Probe-vehicle data and Image-based vehicle data to understand PE(Percentage Error). According to the study results, the PE of the Probe-vehicle data showed a 95% confidence level within an 8-second interval, which was chosen as the appropriate collection interval for Probe-vehicle data. It is our hope that the developed guidelines facilitate C-ITS, and autonomous driving service providers will use more reliable Space Mean Speed data to develop better related C-ITS and autonomous driving services.

• Journal of Institute of Control, Robotics and Systems
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• v.5 no.1
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• pp.25-32
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• 1999

교류전동기 구동을 위한 산업용 전력전자 시스템은 전력회생용 양방향 컨버터, VVVF 인버터, 교류전동기 벡터제어기, 및 다양한 전기ㆍ기계적 연계 장치들을 포함하는 전기기계 복합시스템 특성을 지니기 때문에 전체 시스템에 대한 컴퓨터 시뮬레이션이 용이하지 않다. 일반적으로 이러한 복잡성을 해결하기 위한 방안으로서 시스템을 근사화시키고 이에 대한 수학적인 등가모델을 유도한 후 이를 이용하여 시뮬레이션을 행하고 있지만, 이 경우 실계통의 다이나믹특성을 정확히 표현할 수 없기 때문에 시뮬레이션 신뢰성이 저하될 수 있다 본 논문에서는 가변구조 제어기법에 의해 역률1 제어기능을 갖는 PWM 컨버터, VVVF 인버터 및 유도기 간접벡터제어기 둥을 포함하는 유도전동기 구동전력전자 시스템을 다이나믹 노드 기법(Dynamic Node Technique DNT)과 시뮬링크(Simulink)를 이용하여 실제회로 구성상태와 유사한 형태로 시뮬링크 윈도우상에서 설계하고, 이를 통해 시뮬레이션을 행할 수 있는 기법을 제시한다. 시뮬레이션 결과를 통하여 전력전자 시스템의 특성과 제시된 다이나믹 노드 기법과 시뮬링크를 이용한 시뮬레이션 기법의 유용성을 보였다.