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권오흠 釜慶大學校 2002 釜慶大學校 論文集 Vol.7 No.-
In this paper, we consider the problem of -fault tolerant permutation routing, in which each node is the source of one packet and, at the same time, is the destination of one packet. For each packet, identical copies of it must be delivered to the destination, along the node-disjoint paths, respectively. We consider the wrap-arounded -way Benes networks and present a randomized -fault tolerant permutation routing algorithm in which, for any link within the network, the number of packets that pass the link is bounded by with high probability.
권오흠 釜慶大學校 2000 釜慶大學校 論文集 Vol.5 No.-
A general parallel job scheduling problem is considered. A job can be processed in parallel on one of several alternative subsets of processors. The processing time of the job depends on the subset of processors assigned to the job. We first show the hardness of approximating the problem in the general setting. Next we focus on linear array network of processors. We give an approximation algorithm of ratio for nonpreemptive scheduling, and another algorithm of ratio 2 for preemptive scheduling. Finally, we give a nonpreemptive scheduling algorithm of ratio for two dimensional meshes.
Localization through Map Stitching in Wireless Sensor Networks
Oh-Heum Kwon,Ha-Joo Song IEEE 2008 IEEE transactions on parallel and distributed syst Vol.19 No.1
<P>Node localization is an essential problem in ad hoc wireless sensor networks. Map stitching is a type of localization algorithm that has received a great deal of attention recently. In this algorithm, the network is divided into small overlapping sub-regions, each of which creates a local map. Then, the local maps are stitched together to form a single global map. In this paper, we first propose a new technique for map-to-map stitching that exploits every available distances between two maps. Next, we propose a few anchor-free localization algorithms based on our stitching technique. We experimentally studied the performance of our algorithms under various settings. The results show that our method achieves a significant performance improvement upon the existing method.</P>
The Effects of Stitching Orders in Patch-and-Stitch WSN Localization Algorithms
Oh-Heum Kwon,Ha-Joo Song,Sangjoon Park IEEE 2009 IEEE transactions on parallel and distributed syst Vol.20 No.9
<P>A 'patch-and-stitchrdquo localization algorithm divides the network into small overlapping subregions. Typically, each subregion consists of a node and all or some of its neighbors. For each subregion, the algorithm builds a local map, called a patch, which is actually an embedding of the nodes it spans in a relative coordinate system. Finally, the algorithm stitches those patches to form a single global map. In a patch-and-stitch algorithm, the stitching order makes an influence on both the performance and the complexity of the algorithm. In this paper, we present a formal framework to deal with stitching orders in patch-and-stitch localization algorithms. In our framework, the stitching order is determined by a stitching scheme and the stitching scheme consists of a stitching policy and a potential function. The potential function is to predict how well a patch will be stitched if patches are stitched according to a given partial order. The stitching policy is a mechanism that determines the stitching order based on the predictions by the potential function. We present various stitching schemes and evaluate them through simulations. In addition, we apply the patch-and-stitch strategy into the anchor-based localization and propose a clustering-based localization algorithm. A potential function is used to partition the network into clusters each of which is centered at an anchor node. For each cluster, a cluster map is constructed via the anchor-free localization algorithm. Then, those cluster maps are combined to form a single global map. We propose a stitching technique for combining those cluster maps and analyze the performance of the algorithm by simulations.</P>
권오흠(Oh-Heum Kwon),김숙연(Sook-Yeon Kim) 한국컴퓨터정보학회 2005 韓國컴퓨터情報學會論文誌 Vol.10 No.5
무선 센서 네트워크에서 인접성 정보만 가지고 두 홉 이내의 노드간의 거리를 추정하는 기법을 제안한다. 이 기법은 인접성 정보만 가지고 노드들의 위치를 측정하는 기존의 알고리즘들의 성능의 한계를 대폭 극복하게 해줄 뿐만 아니라, 두 홉 떨어진 노드간의 거리를 추정하게 해주는 최초의 방법이기도 하다. 공통 이웃의 개수를 헤아림으로써 두 노드간의 거리를 추정하는데, 이는 두 노드를 중점으로 하는 두 단위디스크의 공통면적에 공통 이웃의 개수가 비례한다는 가정을 기반으로 한다. 시뮬레이션을 통해 성능을 분석한 결과 거리추정 오차율은 10%에서 20%정도이다. 한편 본 방법을 분산 알고리즘으로 활용하기 위해서 필요한 메시지 개수는 겨우 노드 개수의 두 배이다. In wireless sensor networks, an estimation method is proposed for distances between nodes within two hops. The method uses only proximity information of nodes without physical distance measurements. It drastically improves the performance of localization algorithms based on proximity information. In addition, it is the first method that estimates distances between nodes exactly in two hops. The distances are estimated from the number of common neighbors under an assumption that the number of common neighbors is proportional to the intersection of two unit disks centered at the two nodes. Simulation analysis shows that the estimation error is roughly from 10 to 20 percent of real distances. Meanwhile, the number of messages required by a distributed algorithm realizing this method is only two times the number of nodes.
센서네트워크 위치인식을 위해 GPS가 제공하는 위치정보와 TWR 방식으로 측정된 노드간의 거리 정보를 융합하는 기법
권오흠(Oh-Heum Kwon),변상구(Sang Gu Byeon),김상훈(Sang Hun Kim),이노복(Noh Bok Lee) 한국정보과학회 2012 정보과학회논문지 : 정보통신 Vol.39 No.1
센서네트워크 위치인식이란 앵커노드들의 위치정보와 노드들 간의 측정된 거리 정보를 이용하여 노드들의 위치를 결정하는 과정을 말한다. 본 논문에서는 각각의 앵커노드가 GPS 수신기를 장착하고 있고, GPS 수신 위치를 자신의 위치로 사용하는 경우를 다룬다. 일반적으로 센서네트워크 위치인식에서 앵커노드의 위치는 신뢰할만한 것으로 간주된다. 그런데 GPS 위치의 정확도는 종종 응용분야가 요구하는 수준에 미치지 못할 수 있다. 더구나 환경에 따라서는 GPS 보다 상대적으로 더 정확한 거리측정 기술들도 존재한다. Nanotron사의 NanoLoc RF에서 사용되는 TWR 거리 측정 기술은 그 한 예이다. 본 논문에서는 GPS가 제공한 위치정보와 노드들 간의 거리 측정 정보를 효과적으로 융합하여 보다 향상된 위치인식을 달성하는 방법에 대해서 다룬다. 즉, GPS가 수신한 위치를 그대로 앵커 노드의 위치로 사용하는 대신 노드들 간의 거리 측정 정보를 이용하여 보정함으로써 보다 나은 위치 인식을 달성하는 것을 목표로 한다. 이를 위한 세 가지 알고리즘을 제시하고 그 결과를 실험을 통하여 분석하였다. Localization refers to the process of determining positions of nodes in wireless sensor network based on the positions of a few anchor nodes and the measured distances between nodes. This paper concerns the situation in which each anchor node equips a GPS receiver and uses the received GPS location as its position. Majority of localization algorithms developed so far assume that the given positions of anchor nodes are trustable. The accuracy of GPS is very often not good enough to satisfy the requirement of the application. Moreover, there exist some ranging technologies that outperform the GPS in their accuracies. The TWR ranging technology adopted by NanoLoc RF chip, developed by Nanotron, is one of them. In this paper, we focus on how to fuse two types of measurement, the GPS locations and the ranging results, to produce better localization. In other words, instead of using the GPS-received positions as positions of anchors, we try to compensate them using the measured distances between nodes. We propose three different algorithms and analyse their performance through experiments.