• Proceedings of the Korea Multimedia Society Conference
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• 2002.05c
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• pp.479-484
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• 2002

본 논문에서는 다중 사용자 간의 상호 작용과 공동 작업을 가능하게 하는 3차원 그래픽 기반의 가상 현실 시스템인 YVES(Yonsei Virtual Environment System) 의 성능향상을 위한 아바타 객체의 효과적인 동기화 방법에 대하여 제안하였다. YVES 는 연세대학교 컴퓨터과학과 멀티미디어 연구실에서 2001년도에 개발된 시스템이다. YVES의 사용자간 동기화 알고리즘은 기존의 방법에 비해 객체의 Poping현상을 없애고 동기화를 유지한 점에서 개선되었다고 할 수 있었다. 그러나 원래의 경로와는 변화된 다른 경로가 설정된다는 것과 이동이 완료되었을 때 수정된 경로로 향한 객체 진행 방향을 완료시점에서 원래의 진행방향으로 수정해야 항으로써 자연스럽지 못한 움직임을 보인다는 것이 문제점으로 지적되었다. 이를 보완하기 위해서 본 논문에서는 기존의 움직임 벡터를 새로 움직여야 할 움직임 벡터에 반영하여 새로운 경로가 원래의 경로와 보다 근접할 수 있도록 하고, 이동의 완료시점에서 객체가 향하는 방향이 원래 경로로 이동했을 경우와 동일하도록 하는 알고리즘을 제안하고, 각 알고리즘을 동일한 이동경로를 적용하여 비교하였다.

• Proceedings of the Korea Multimedia Society Conference
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• 2004.05a
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• pp.322-325
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• 2004

인터넷 통신과 무선 이동 통신의 발달은 최적 경로 탐색이 인터넷 웹 페이지를 통하여 서비스될 수 있도록 하였으며, CNS(Car Navigation System)를 이용한 서비스도 가능하도록 하였다. 더욱이 개인용 휴대통신 장비인 PDA나 휴대폰을 이용하여서도 그 서비스가 제공되고 있지만, 휴대폰에서의 최적 경로 표현은 화면 크기의 제약성 때문에 많은 정보를 나타내기 어려우며, 휴대폰의 환경에 맞도록 기존의 공간 DB를 수정하는 것 또한 많은 비용과 시간이 필요하다. 이에 본 논문에서는 기존의 DB를 이용하면서 사용자가 입력한 출발지와 목적지 정보를 이용하여 최적 경로 탐색을 수행하고, 탐색된 최적 경로를 일반화 알고리즘을 이용하여 휴대폰의 작은 화면에서 사용자가 쉽게 인지할 수 있도록 약도화 하는 알고리즘을 제안한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.11
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• pp.2886-2896
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• 1996

The Type of Service based multicast routing algorithm is necessary to support efficiently herogeneous applications in ATM network. In this paper I propose the Constrained Multicast Tree with Virtual Destination(DMTVD) heuristic algorithm as least cost multicast routing algorithm. The service is categorized into two types, as delay sensitive and non in CMTVD algorithm. For the delay sensitive service type, the cost optimized route is the Minimum Cost Stenier Tree connecting all the destination node group, virtual destination node group and source node with least costs, subject to the delay along the path being less than the maximum allowable end to end delay. The other side for the non-delay sensitive service, the cost optimized route is the MCST connecting all the multicast groups with least costs, subject to the traffic load is balanced in the network. The CMTVD algorithm is based on the Constrained Multicasting Tree algorithm but regards the nodes branching multiple destination nodes as virtural destination node. The experimental results show that the total route costs is enhanced 10%-15% than the CTM algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.11B
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• pp.900-910
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• 2004

Route failure is mainly caused by mobility of mobile host in ad hoc networks. Route failure, which may lead to sudden packet losses and delays, is losing the route from source to destination. In this situation, TCP assumes that congestion has occurred within the network and also initiates the congestion control procedures. Congestion control algorithm provides the means for the source to deal with lost packets. TCP performance in ad hoc environments will be degraded as TCP source cannot distinguish congestion from route failure. In this paper, we propose TCP-P as pre-detection approach to deal with route failure. TCP-P freezes TCP through pre-detection of route failure. Route failure information of the proposed mechanism is obtained not by routing protocol but by MAC protocol. The intermediated node, obtaining route failure information by its MAC layer, relays the information to TCP source and lets TCP source stop the congestion control algorithm. Results reveal that TCP-P responding with proactive manner outperforms other approaches in terms of communication throughput under the presence of node mobility.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2012.10a
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• pp.323-325
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• 2012

본 논문에서는 거리정보에 기반을 두지 않은 방식(range-free)에서 라우팅 에너지 효율성을 고려한 ALPS(Ad hoc network Localized Positioning System) 알고리즘을 제안한다. 관련하여 기존의 대표적인 관련 연구로는 DV-Hop 알고리즘이 있다. 이는 앵커 노드와 앵커 노드사이의 미지 노드들의 거리를 홉 수로 나누어 노드 사이의 거리를 구하고 삼각측량법을 이용하여 노드의 좌표를 계산한다. 하지만 이 경우 앵커 노드와 미지노드 사이의 거리를 홉 수로 나눈 한 홉 거리가 모두 동일하다고 가정하였고, 이에 사용되는 앵커노드간의 평균 거리를 사용하여 노드간의 거리정보를 구하게 되어 각 중계노드는 고정된 경로에서만 거리 정보를 알 수 있다. 본 논문에서 제안되는 ALPS 알고리즘은 계층적 클러스터 단위에 소속된 임의의 노드에 대한 위치정보를 제공하는 방법을 제안한다. 제안된 알고리즘에 따른 위치정보를 사용 할 경우 기존의 DV-hop방식에 따른 노드의 위치정보를 사용한 경우보다 보다 최적화된 에너지 소모를 유지할 수 있는 경로 알고리즘을 최종적으로 제공하는데 연구의 목적이 있다. 본 논문에서는 상기 두 가지 방식의 위치정보에 따른 라우팅에서 소모되는 에너지 관계를 비교하여 보다 최적화된 에너지 경로 알고리즘이 제공되는 결과를 검증하고 보여주고자 한다.

• Journal of Korean Society of Transportation
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• v.19 no.4
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• pp.85-96
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• 2001

This paper discusses the problem of finding the Origin-Destination(O-D) shortest path in urban road networks that have variable special qualifies such as time windows for passing as well as geometrical special qualities such as U-turn and left-turn prohibition. The focus of this paper is motivated by the problem of finding minimum travel time paths for an advanced traveler information system (ATIS) in the context of intelligent transportation system(ITS) application. The transportation network with variable and geometrical special qualities is a more realistic representation of the urban road network in the real word. But, the traditional and existing shortest path algorithms can not search practical shortest path that variable special quality is reflected. This paper presents a shortest path algorithm which can search reasonable shortest path information for the urban ATIS application within a real time. The algorithm is based on genetic algorithm(GA). The high performance of the proposed algorithm is demonstrated by computer simulations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.12C
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• pp.1215-1227
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• 2002

This paper presents a genetic algorithmic approach to shortest path (SP) routing problem. Variable-length chromosomes (strings) and their genes (parameters) have been used for encoding the problem. The crossover operation that exchanges partial chromosomes (partial-routes) at positionally independent crossing sites and the mutation operation maintain the genetic diversity of the population. The proposed algorithm can cure all the infeasible chromosomes with a simple repair function. Crossover and mutation together provide a search capability that results in improved quality of solution and enhanced rate of convergence. Computer simulations show that the proposed algorithm exhibits a much better quality of solution (route optimality) and a much higher rate of convergence than other algorithms. The results are relatively independent of problem types (network sizes and topologies) for almost all source-destination pairs.

• Korean Journal of Ecology and Environment
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• v.41 no.3
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• pp.275-282
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• 2008

Water hardness is a significant parameter as related to aquatic toxicity of some heavy metals. Hardness dependent metals include cadmium, copper, chromium (III), nickel, lead, zinc and silver. Developed countries have applied the hardness correction procedure to derive the water quality criteria for protecting the aquatic organisms. In the present study, we investigated the hardness correction algorithms used in United States of America, European Union, Australia/New Zealand, and Canada, and analyzed the details associated with those algorithms. Toxicity values of heavy metals were definitely different after hardness correction for all of algorithms analyzed. We found that the hardness corrected toxicity values followed by the algorithms of USA and Australia/New Zealand were very similar or same, however they were slightly different for cadmium at the hardness less than 30 mg $CaCO_3\;L^{-1}$. Among the hardness correction algorithms studied, the algorithm used in Australia/New Zealand appears to be a good choice to apply in Korean situation due to its simplicity compared to the algorithm of USA.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.5
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• pp.379-387
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• 2019

The complexity of path planning for visiting multiple mission points is even larger than that of single pair path planning. Deciding a path for visiting n mission points requires conducting $n^2+n$ times of single pair path planning. We propose Multiple Mission $D^*$ Lite($MMD^*L$) which is an optimal path planning algorithm for visiting multiple mission points in dynamic environments. $MMD^*L$ reduces the complexity by reusing the computational data of preceding single pair path planning. Simulation results show that the complexity reduction is significant while its path optimality is not compromised.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.05a
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• pp.835-838
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• 2008

Many researches on hierarchical path search have been studied so far. Even though partitioning regions is essential part, the researches are not enough. This paper proposes two efficient methods to partition regions: 1)a method based on voronoi algorithm in which a major node is central point of a region, 2) a method based on fired grid that partitions regions into major and minor. The performances of the proposed methods are compared with the conventional hierarchical path search method in which a region is formed by the boundary line of nearest 4 points of a major node in terms of the path search time and the accuracy. The results obtained from the experiments show that the method based on voronoi achieves short execution time and the method based grid achieves high accuracy.