• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권5호
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• pp.1303-1315
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• 2012

In the draft of the IEEE 802.11s standard, a tree topology is established by the proactive tree-building mode of the Hybrid Wireless Mesh Protocol (HWMP). It is used for cases in which the root station (e.g., gateway) is an end point of the majority of the data connections. In the tree topology, the root or central stations (e.g., parent stations) are connected to the other stations (e.g., leaves) that are one level lower than the central station. Such mesh stations are likely to suffer heavily from contention in bottleneck links when the network has a high traffic load. Moreover, the dependence of the network on such stations is a point of vulnerability. A failure of the central station (e.g., a crash or simply going into sleep mode to save energy) can cripple the whole network in the tree topology. This causes performance degradation for end-to-end transmissions. In a connected mesh topology where the stations having two or more radio links between them are connected in such a way that if a failure subsists in any of the links, the other link could provide the redundancy to the network. We propose a scheme to utilize this characteristic by organizing the network into concentric tiers around the root mesh station. The tier structure facilitates path recovery and congestion control. The resulting mode is referred to as Tier-based Proactive Path Selection Mode (TPPSM). The performance of TPPSM is compared with the proactive tree mode of HWMP. Simulation results show that TPPSM has better performance.

• 한국조리학회지
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• 제24권2호
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• pp.1-7
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• 2018

This study aims to find what attributes of consumer satisfaction are more important when consumers choose coffee shops. Factors when customers choose coffee shops that are considered to be more crucial, such as taste, price, brand, and atmosphere, were tested and also relations between satisfaction and revisit were studied. As a result, factors as 'taste', 'price', 'brand', and 'atmosphere' were found to significantly affect satisfaction; in addition, the path that satisfaction leads to revisit was found to be significant. However, consumers' coffee shop selection attributes differed depending on their psychological consumption value. The path-coefficients from taste and price to satisfaction were more significant in the function-oriented group, meanwhile the path-coefficient from brand to satisfaction was significant in the emotion-oriented group (+) and the function-oriented group (-). The results of this study suggest attributes of selecting coffee shops and provide meaningful implications of consumer value when they choose the attributes.

• 한국ITS학회 논문지
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• 제12권3호
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• pp.87-95
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• 2013

본 논문에서는 다중 홉 시스템에서 하나의 홉에 대한 채널 정보만을 이용하는 효율적인 부분 중계 노드 선택(efficient partial relay selection, EPRS) 기법에 대한 아웃티지 확률을 레일레이 페이딩 채널에서 분석한다. 특히, 디코딩 후 전달 중계 기반의 EPRS 기법에 대한 정확한 아웃티지 확률의 식을 유도한다. 또한, 다중 홉 시스템에서 EPRS 기법의 실효성을 확인하기 위하여, 임의의 중계 경로에서 종단간 신호 대 잡음비와 각 홉의 신호 대 잡음비의 상관관계를 분석한다. 그리고, 수치적 결과를 통해 EPRS 기법과 모든 채널 정보를 이용하는 중계 노드 선택 기법의 아웃티지 성능을 비교한다.

• The Journal of Asian Finance, Economics and Business
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• 제6권1호
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• pp.187-194
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• 2019

This study examined that what attributes of student satisfaction are more important when students use university cafeterias. Factors that are considered to be more crucial when students use a cafeteria, such as menu, taste, price, and cleanliness, were tested. Based on the research of previous studies, it assumed that the selection attributes of students' cafeteria were menu, taste, price, and cleanliness. With 301 surveyed questionnaires, the study was carried out by AMOS 23.0 and the Structural Equation Model was used for examining the hypotheses as statistical method in this study. In consequence of the hypothesis test on the main effect, the factors such as the menu, taste, price and cleanliness were found to significantly affect satisfaction. Then, the moderating role of gender, age and allowance was analyzed. However, students' university cafeteria selection attributes differed depending on their allowance only. The path coefficients from menu to satisfaction were more significant in the group with a smaller allowance, while the path coefficient from price to satisfaction was more significant in the group with a larger allowance. The study analyzed that the effect of selection attribute of students' cafeteria on the satisfaction, and influence of students' allowance, and provide meaningful implications when they choose the attributes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권11호
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• pp.5276-5298
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• 2019

Internet of Things (IoT) based sensor networks have gained unprecedented popularity in recent years. With the exponential explosion of the objects (sensors and mobiles), the bandwidth and the speed of data transmission are dwarfed by the anticipated emergence of IoT. In this paper, we propose a novel heterogeneous IoT model integrated the power line communication (PLC) and WiFi network to increase the network capacity and cope with the rapid growth of the objects. We firstly propose the mean transmission delay calculation algorithm based the 3D Markov chain according to the multi-priority of the objects. Then, the attractor selection algorithm, which is based on the adaptive behavior of the biological system, is exploited. The combined the 3D Markov chain and the attractor selection model, named MASM, can select the optimal path adaptively in the heterogeneous IoT according to the environment. Furthermore, we verify that the MASM improves the transmission efficiency and reduce the transmission delay effectively. The simulation results show that the MASM is stable to changes in the environment and more applicable for the heterogeneous IoT, compared with the other algorithms.

• 대한안전경영과학회지
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• 제13권2호
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• pp.103-113
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• 2011

This research is to select a path planning algorithm to maximize survivability for Unmanned Aerial Vehicle(UAV). An UAV is a powered pilotless aircraft, which is controlled remotely or autonomously. UAVs are currently employed in many military missions(surveillance, reconnaissance, communication relay, targeting, strike etc.) and a number of civilian applications(communication service, broadcast service, traffic control support, monitoring, measurement etc.). In this research, a mathematical programming model is suggested by using MRPP(Most Reliable Path Problem) and verified by using ILOG CPLEX. A path planning algorithm for UAV is selected by comparing of SPP(Shortest Path Problem) algorithms which transfer MRPP into SPP.

• 한국시뮬레이션학회논문지
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• 제20권4호
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• pp.31-40
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• 2011

센서 노드는 악의적인 공격자들에 의해 물리적인 공격들에 쉽게 노출된다. 공격자는 훼손 노드를 이용하여 센서 네트워크에 다양한 공격을 발생시킬 수 있다. 그 중 응용 계층에서 발생하는 허위 보고서 삽입 공격은 훼손된 노드를 통해 네트워크 내에 위조 보고서를 주입한다. 주입된 위조 보고서는 BS까지 전달될 경우 허위 경보뿐만 아니라 노드의 불필요한 에너지 소모를 유발한다. 이러한 공격을 방어하기 위해 통계적 여과 기법은 BS까지 전달되는 허위 보고서를 전달 과정 중 가능한 빨리 여과시키기 위해 제안되었다. 이 기법의 성능 향상을 위해 제안된 기법 중 경로 갱신 기법은 통계적 여과 기법의 탐지 능력 유지하고 노드의 균형 있는 에너지 소모를 위해 제안되었다. 본 논문은 경로 경신 방법에서 경로 갱신에 필요한 에너지의 효율적인 소비를 위해 보안 경로 주기 결정 방법을 제안한다. 보안 경로 주기를 선택하기 위해 BS에서 센서 노드들의 홉 수와 보고서 전송량을 고려하여 평가 함수를 통해 결정한다. 그리고 시뮬레이션을 통해 위 3가지 기법들과 제안 기법을 비교하여 에너지 효율성을 평가한다. 그러므로 제안 기법은 보안 경로 설정을 유지하면서, 네트워크 내에 균형 있는 에너지 소비의 효율을 높인다.

• 한국시뮬레이션학회논문지
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• 제20권3호
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• pp.69-78
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• 2011

대규모 센서 네트워크를 구성하는 센서 노드는 개방된 무인 환경에서 동작한다. 악의적인 공격자는 일부 센서 노드를 탈취 하여 허위 보고서를 주입할 수 있다. 통계적 여과 기법은 이러한 허위 보고서 주입 공격에 대응하기 위한 기법으로 보고서 전달 과정 중에 허위 보고서를 검출하고 여과할 수 있는 방법을 제안하였다. 통계적 여과 기법에서는 적절한 전달 경로 설정을 통하여 허위 보고서 검출 성능 향상뿐만 아니라 에너지 효율 또한 높일 수 있다. 하지만 네트워크의 위상 변화와 노드의 에너지고갈 등의 다양한 환경 변화로 인하여 전달 경로를 재설정해야 하는 경우가 빈번히 발생한다. 빈번한 경로 재설정은 과도한 에너지 소모를 유발하므로 적절한 경로 재설정 주기를 결정하는 것은 매우 중요하다. 본 논문에서는 센서 네트워크의 제안된 에너지를 효율적으로 사용하기 위한 영역별 경로 재설정 주기 결정 기법을 제안한다. 제안 기법은 퍼지 시스템을 이용해 각 영역의 경로 재설정 주기를 동적으로 결정한다. 또한 주기가 결정된 영역에 대해 적절한 보안 수준을 결정하고 해당 영역은 이를 적용하여 경로를 재설정한다. 시뮬레이션을 통하여 제안 기법이 경로 재설정에 사용되는 에너지 소모량을 최대 50% 이상 감소시켰음을 확인하였다.

• Journal of Electrical Engineering and Technology
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• 제8권4호
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• pp.879-888
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• 2013

This paper addresses the vision based local path planning system for obstacle avoidance. To handle the obstacles which exist beyond the field of view (FOV), we propose a Panoramic Environment Map (PEM) using the MDGHM-SIFT algorithm. Moreover, we propose a Complexity Measure (CM) and Fuzzy logic-based Avoidance Motion Selection (FAMS) system to enable a humanoid robot to automatically decide its own direction and walking motion when avoiding an obstacle. The CM provides automation in deciding the direction of avoidance, whereas the FAMS system chooses the avoidance path and walking motion, based on environment conditions such as the size of the obstacle and the available space around it. The proposed system was applied to a humanoid robot that we designed. The results of the experiment show that the proposed method can be effectively applied to decide the avoidance direction and the walking motion of a humanoid robot.

• 한국정밀공학회지
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• 제11권6호
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• pp.28-41
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• 1994

An efficient algorithm is proposed to select the proper tools and generate their paths for NC rough cutting of dies and molds with sculptured surfaces. Even though a milling process consists of roughing, semi-finishing, and finishing, most material is removed by a rough cutting process. Therfore it can be said that the rough cutting process occupy an important portion of the NC milling process, and accordingly, an efficient rough cutting method contributes to an efficient milling process. In order work, the following basic assumption is accepted for the efficient machining. That is, to machine a region bounded by a profile, larger tools should be used in the far inside and the region adjacent to relatively simple portion of the boundary while smaller tools are used in the regions adjacent to the relatively complex protion. Thus the tools are selected based on the complexity of the boundary profile adjacent to the region to be machined. An index called cutting path ratio is proposed in this work as a measure of the relative complexity of the profile with respect to a tool diameter. Once the tools are selected, their tool paths are calculated starting from the largest to the smallest tool.