• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.1
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• pp.115-120
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• 2013

There are lots of vulnerability and chance to be attacked in wireless sensor networks, which has many applications. Among those attacks, sybil attack is to generate a lot of false node and to inject false information into networks. When a user uses such false information without recognizing the attack, there might be a disaster. Although authentication method can be used to protect such attack, the method is not a good choice in wireless sensor networks, where sensor nodes have a limited battery and low power. In this paper, we propose a novel method to detect sybil attack with a little extra overhead. The proposed method use the characteristics that there is a weak connection between a group of normal nodes and a group of false nodes. In addition, the method uses energy aware routing based on random routing and adds a little information into the routing. Experimental results show that the proposed method detects false node by more than 90% probability with a little energy overhead.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.25 no.5
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• pp.1281-1291
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• 2015

Compared to the past, people can control end devices via open channel. Although this open channel provides convenience to users, it frequently turns into a security hole. In this paper, we propose a new human-centered security risk analysis method that puts weight on the relationship between end devices. The measure derives from the concept of entropy rate, which is known as the uncertainty per a node in a network. As there are some limitations to use entropy rate as a measure in comparing different size of networks, we divide the entropy rate of a network by the maximum entropy rate of the network. Also, we show how to avoid the violation of irreducible, which is a precondition of the entropy rate of a random walk on a graph.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.3
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• pp.491-498
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• 2016

The software defined networks implement a software network control plane, which is physically separated from the data plane. For wide area software defined network deployments, multiple controllers are required, and the placement of these controllers influences importantly the performance of the software defined networks. This paper proposes a Tabu search algorithm, which is one of the meta heuristic algorithms, for an efficient controller placement in software defined networks. In order to efficiently obtain better results, we propose new neighborhood generating operations, which are called the neighbor position move and the neighbor number move, of the Tabu search algorithm. We evaluate the performances of the proposed algorithm through some experiments in terms of the minimum latency and the execution time of the proposed algorithm. The comparison results show that the proposed algorithm outperforms the existing genetic algorithm and random method under various conditions.

• The Journal of the Korea Contents Association
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• v.18 no.1
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• pp.64-75
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• 2018

With the development of location-aware technologies and the activation of smart phones, location based social networks(LBSN) have been activated to allow people to easily share their location. In particular, studies on recommending the location of user interests by using the user check-in function in LBSN have been actively conducted. In this paper, we propose a location recommendation scheme considering time and user activities in LBSN. The proposed scheme considers user preference changes over time, local experts, and user interest in rare places. In other words, it uses the check-in history over time and distinguishes the user activity area to identify local experts. It also considers a rare place to give a weight to the user preferred place. It is shown through various performance evaluations that the proposed scheme outperforms the existing schemes.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.2
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• pp.303-310
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• 2014

We show improved throughput scaling laws for an ultra-wide band (UWB) ad hoc network, in which n wireless nodes are randomly located. First, we consider the case where a modified hierarchical cooperation (HC) strategy is used. Then, in a dense network of unit area, our result indicates that the derived throughput scaling depends on the path-loss exponent ${\alpha}$ for certain operating regimes due to the power-limited characteristics. It also turns out that the HC protocol is dominant for 2 < ${\alpha}$ < 3 while using the nearest multihop (MH) routing leads to a higher throughput for ${\alpha}{\geq}3$. Second, the impact and benefits of infrastructure support are analyzed, where m base stations (BSs) are regularly placed in UWB networks. In this case, the derived throughput scaling depends on ${\alpha}$ due to the power-limited characteristics for all operating regimes. Furthermore, it is shown that the total throughput scales linearly with parameter m as m is larger than a certain level. Hence, the use of either HC or infrastructure is helpful in improving the throughput of UWB networks in some conditions.

• Journal of IKEEE
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• v.23 no.2
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• pp.529-533
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• 2019

Combined cycle power plants are often used to produce power. These days prediction of power plant output based on operating parameters is a major concern. This paper presents an approach to using computational intelligence technique to predict the output power of combined cycle power plant. Computational intelligence techniques have been developed and applied to many real world problems. In this paper, tree architectures of fuzzy neural networks are considered to predict the output power. Tree architectures of fuzzy neural networks have an advantage of reducing the number of rules by selecting fuzzy neurons as nodes and relevant inputs as leaves optimally. For the optimization of the networks, two-step optimization method is used. Genetic algorithms optimize the binary structure of the networks by selecting the nodes and leaves as binary, and followed by random signal-based learning further refines the optimized binary connections in the unit interval. To verify the effectiveness of the proposed method, combined cycle power plant dataset obtained from the UCI Machine Learning Repository Database is considered.

• The KIPS Transactions:PartD
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• v.18D no.6
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• pp.501-508
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• 2011

A knowledge map, which has been recently applied in various fields, is discovering characteristics hidden in a large amount of information and showing a tangible output to understand the meaning of the discovery. In this paper, we suggested a knowledge map for research trend analysis based on keyword-relation networks which are constructed by using a database of the domestic journal articles in the computer engineering field from 2000 through 2010. From that knowledge map, we could infer influential changes of a research topic related a specific keyword through examining the change of sizes of the connected components to which the keyword belongs in the keyword-relation networks. In addition, we observed that the size of the largest connected component in the keyword-relation networks is relatively small and groups of high-similarity keyword pairs are clustered in them by comparison with the random networks. This implies that the research field corresponding to the largest connected component is not so huge and many small-scale topics included in it are highly clustered and loosely-connected to each other. our proposed knowledge map can be considered as a approach for the research trend analysis while it is impossible to obtain those results by conventional approaches such as analyzing the frequency of an individual keyword.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.6
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• pp.65-73
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• 2016

Peer-to-Peer (P2P) systems with super-peer overlay networks show combined advantages of both hybrid and pure P2P systems. Super-peer is a special peer acting as a server to a cluster of generic peers. Organizing a super-peer network is one of important issues for P2P systems with super-peer networks. Conventional P2P systems are based on two-level hierarchies of peers. One is a layer for generic peers and the other is for super-peers. And it is usual that super-peer networks have forms of random graphs. However, for accommodating a large-scale collection of generic peers, the super-peer network has also to be extended. In this paper, we propose a scheme of hierarchically constructing super-peer networks for large-scale P2P systems. At first, a two-level tree, called a simple super-peer network, is proposed, and then a scheme of generalizing and then extending the simple super-peer network to multi-level super-peer network is presented to construct a large-scale super-peer network. We call it an extended super-peer network. The simple super-peer network has several good features, but due to the fixed number of levels, it may have a scalability problem. Thus, it is extended to k-level tree of a super-peer network, called extended super-peer network. It shows good scalability and easy management of generic peers for large scale P2P system.

• Journal of KIISE:Computing Practices and Letters
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• v.16 no.4
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• pp.421-426
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• 2010

Due to the ease of deployment and the extended coverage, wireless mesh networks (WMNs) are gaining popularity and research focus. For example, the routing protocols that enhance the throughput on the WMNs and the link quality measurement schemes are among the popular research topics. However, most of these works assume that the locations of the mesh routers are predetermined. Since the operators in an Indoor mesh network can determine the locations of the mesh routers by themselves, it is essential to the WMN performance for the mesh routers to be initially placed by considering the performance issues. In this paper, we propose a mesh router placement scheme based on genetic algorithms by considering the characteristics of WMNs such as interference and topology. There have been many related works that solve similar problems such as base station placement in cellular networks and gateway node selection in WMNs. However, none of them actually considers the interference to the mesh clients from non-associated mesh routers in determining the locations of the mesh routers. By simulations, we show that the proposed scheme improves the performance by 30-40% compared to the random selection scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.6B
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• pp.350-357
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• 2007

The IEEE 802.15.3 high-rate WPAN has been developed to communicate with devices within l0m. A piconet consists of one Piconet Coordinator (PNC) and several devices. The devices associated with a parent piconet can become child PNCs in order to form child piconets. A mesh network made up of a parent piconet and several child piconets can support multi-hop communications. In this paper, we analyze the maximum level and the avaliable superframe size to make the best use of bandwidth for multi-hop communications, and compare the analysis with the simulation results in terms of time to discover devices for multi-hop communications. The average number of levels in mesh networks is shown to be about 1.9 when the number of devices increases within a fixed area. We have also shown that the maximum available superframe size is 52ms and the discovery time is approximately 155ms.