• Journal of KIISE:Databases
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• v.29 no.1
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• pp.79-88
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• 2002

Data on the Internet are usually represented and transfered as XML. the XML data is represented as a tree and therefore, object repositories are well-suited to store and query them due to their modeling power. XML queries are represented as regular path expressions and evaluated by traversing each object of the tree in object repositories. Several indexes are proposed to fast evaluate regular path expressions. However, in some cases they may not cover all possible paths because they require a great amount of disk space. In order to efficiently evaluate the queries in such cases, we propose an optimized traversing which combines the signature method and block traversing. The signature approach shrink the search space by using the signature information attached to each object, which hints the existence of a certain label in the sub-tree. The block traversing reduces disk I/O by early evaluating the reachable objects in a page. We conducted diverse experiments to show that the hybrid approach achieves a better performance than the other naive ones.

• Proceedings of the Korean Information Science Society Conference
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• 2005.11b
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• pp.745-747
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• 2005

수많은 웹페이지들이 하이퍼링크를 통해 복잡하게 연결된 그래프 구조를 가지고 있는 웹사이트를 계층적으로 구조화하는 것은 해당 사이트를 검색하고자 할 때, 정보를 재조직화하고 고려해야 할 대안들의 개수를 감소시킨다는 점에서 매우 유용하다. 본 논문은 웹사이트의 의미론적인 계층화를 최적화하기 위하여 사용자의 순회 경로, 즉 웹아크의 중요도 합을 최대화할 수 있는 트리 구조를 생성하였다. 구체적으로 첫째 PageRank에 기반한 웹아크 중요도를 생성하였고, 둘째 Minimum-Cost Arborescence 문제를 이용하여 최적 트리 구조를 생성하였다. 사용자의 질의에 독립적으로 생성된 트리 구조는 웹사이트의 의미 있는 계층 구조로서 사용자로 하여금 해당 사이트를 보다 효과적으로 검색할 수 있도록 도와줄 것이다.

• The KIPS Transactions:PartC
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• v.15C no.3
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• pp.205-212
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• 2008

In the environment with multiple heterogeneous wireless sensor networks with a single point of sensed data collection or a gateway (GW), relay points (RPs) may be required for the energy efficient delivery of sensed data from static or mobile sinks to the GW. The optimal placement of RPs becomes an even more difficult problem if static sinks are dynamically added or the trajectory of mobile sinks can not be known in advance. In order to resolve this problem, we propose a mechanism to deploy RPs in a grid pattern and to use the tree-based relaying network for reducing the cost of the RP and for reducing the control overhead incurred by the route setup from sinks to the GW. For the performance evaluation of our proposed mechanism, we have carried out a numerical analysis on a single route setup from a sink to the GW and, for more general performance evaluations, ns-2 based simulations have been carried out. According to the performance evaluation results, our tree-based relaying network mechanism outperforms that based on AODV in terms of the data delivery time, the network service time and the control overhead.

• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.5
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• pp.981-988
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• 2023

As the usage of unmanned aerial vehicles expands, the development and the demand of related technologies are increasing. As the frequency of operation increases and the convenience of operation is emphasized, the importance of related autonomous flight technology is also highlighted. Establishing a path plan to reach the destination in autonomous flight of an unmanned aerial vehicle is important in guidance and control, and a technology for automatically generating path plan is required in order to maximize the effect of unmanned aerial vehicle. In this study, the optimization research of path planning using rapid-exploring random tree method was performed for increasing the effectiveness of autonomous operation. The path planning optimization method considering the characteristics of the unmanned aerial vehicle is proposed. In order to achieve indexes such as optimal distance, shortest time, and passage of mission points, the path planning was optimized in consideration of the mission goals and dynamic characteristics of the unmanned aerial vehicle. The proposed methods confirmed their applicability to the generation of path planning for unmanned aerial vehicles through performance verification for obstacle situations.

• The Transactions of the Korea Information Processing Society
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• v.2 no.3
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• pp.343-353
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• 1995

The path navigation of autonomous guided vehicle(AGV) or autonomous mobile robot(AMR) assumed that the environment was completely known and the obstacles were fixed. So that, in an environment only partly known or not known at all, the previous works were not successful since the path exploration techniques involved in the work were neither directly applicable nor extensible. In order to improve such problems, this paper was adopted the quadtree technique and proposed the algorithm for an optimal path planning autonomously in an environment and proved a validity through a simulation.

• Journal of Korean Society of Transportation
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• v.26 no.1
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• pp.127-135
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• 2008

Generally, optimum shortest path algorithms adopt single attribute objective among several attributes such as travel time, travel cost, travel fare and travel distance. On the other hand, multi-objective shortest path algorithms find the shortest paths in consideration with multi-objectives. Up to recently, the most of all researches about multi-objective shortest paths are proceeded only in single transportation mode networks. Although, there are some papers about multi-objective shortest paths with multi-modal transportation networks, they did not consider transfer problems in the optimal solution level. In particular, dynamic programming method was not dealt in multi-objective shortest path problems in multi-modal transportation networks. In this study, we propose a multi-objective shortest path algorithm including dynamic programming in order to find optimal solution in multi-modal transportation networks. That algorithm is based on two-objective node-based label correcting algorithm proposed by Skriver and Andersen in 2000 and transfer can be reflected without network expansion in this paper. In addition, we use non-dominated paths and tree sets as labels in order to improve effectiveness of searching non-dominated paths. We also classifies path finding attributes into transfer and link travel attribute in limited transit networks. Lastly, the calculation process of proposed algorithm is checked by computer programming in a small-scaled multi-modal transportation network.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.10
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• pp.4531-4535
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• 2011

In this paper, USN(Ubiquitous Sensor Network) is used in the structure of the tree routing was implemented in embedded systems. Tree Routing in the USN to the sink node to transmit sensor data is one of the techniques. When routing, sensor data is transmitted based on pre-defined ID according hop number. In order to have optimal routing path, the current state of the wireless sector and the sensor node informations were used. Also, received sensor data and the results of the tree routing by implementing an embedded system. This embedded system can be applied to a portable sensor information collecting system.

• Proceedings of the Korean Information Science Society Conference
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• 2003.04d
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• pp.103-105
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• 2003

최근 이동성을 제공하는 시스템이 매우 빠른 속도로 보급되고 있는 추세이며 그 서비스 분야 또한 다양해져 무선 멀티미디어 서비스에 대한 요구가 커지고 있다 멀티미디어 서비스는 많은 데이터 용량을 요구하며, 같은 정보를 여러 사용자들에게 보내야 하는 특징을 갖는다. 이동하는 사용자에게 이와 같은 특징을 갖는 멀티미디어 서비스를 효율적으로 제공하기 위해서는 이동성을 지원하는 효율적인 멀티캐스팅 기법이 필요하다. Mobile If 기반의 이동 네트워크 환경에서 멀티캐스팅을 지원하기 위한 연구는 크게 양방향 터널링 방식과 원격 가입 방식으로 연구되어 왔다 양방향 터널링 방식은 홈 네트워크를 항상 경유함으로 인해 발생하는 데이터 전송 경로의 비최적화와 데이터 중복 전송의 문제를 가지고 있으며, 원격 가입 방식은 빈번한 멀티캐스트 전송 트리의 재구성으로 인한 오버헤드와 서비스 단절의 문제를 가지고 있다. 따라서 본 논문에서는 이동 호스트의 이동 방향 정보를 이용한 자원 예약 기법을 통해 이동 호스트에게 투명한 이동성을 제공하여 서비스의 단절을 줄이고, 가변적인 서비스 범위를 통하여 멀티캐스트 전송 트리의 재구성으로 인한 오버헤드를 줄이는 방법을 제안한다.

• Journal of the Korea Society for Simulation
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• v.18 no.3
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• pp.61-71
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• 2009

The server redirection system replicates contents on replica servers in the distributed network environment. When users make a request for contents, the system can provide the contents much faster than the client-server network system. In the server redirection system, it is the most important to select the optimal replica server with user's information because many replica servers are geographically distributed. And, the system can serve contents to users flexibly if a redirector is well constructed. In this paper, the redirector makes a list of candidates suitable for user conditions by the decision tree method and calculates the availability of each replica server. And, the redirector selects the replica server with the highest availability. This paper also proposes an availability-based server redirection system that predicts the availability of each replica server in order to reduce the workload of replica servers and the repetitive communication messages between a redirector and replica servers. If a user accesses the network path for the replica server selected and noticed by the proposed system, the user can get contents effectively and efficiently.

• Journal of Advanced Navigation Technology
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• v.16 no.2
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• pp.271-277
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• 2012

In this paper, we propose a dynamic tree formation protocol for multiple UAV which is gathering data or accomplishing a mission such as disaster monitoring, environment monitoring, and disaster relief. Especilly, we designed Hop-LQI Weight algorithm to form optimal tree in wireless dynamic environment applying situation of radio signal attenuation over distance and implemented our algorithm in MSP 430 K-mote sensor platform using TinyOS codes. We verified performance of our algorithm by comparing average link setup time by the number of nodes with minimum LQI, link cost calculation method in wireless communication.