• The KIPS Transactions:PartC
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• v.13C no.4 s.107
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• pp.447-454
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• 2006

An ad-hoc network routing protocol, AODV(Ad-hoc On-demand Distance Vector) initially uses ERS(Expanding Ring Search) algorithm to control the RREQ(Route Request) retransmission in the route discovery process. Because ERS uses the fixed NTT(Node Travesal Time), it does not reflect accurately ad-hoc network environment. In this paper, we propose an improved ERS algorithm which lowers the retransmission rate. It uses RREP(Route Reply) and gives different weights in NTT of each node in accordance with the adjacency to an originating node. To show the effectiveness of the proposed algorithm, we perform a simulation using ns2. The simulation results showed that the proposed algorithm has better performance than existing algorithms.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.105-105
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• 2017

최근 우리나라에서는 국지성호우로 인해 발생하는 돌발홍수에 방어하지 못하는 소규모 저수지에 대한 붕괴사고가 빈발하고 있다. 붕괴된 저수지를 살펴보면, 대체적으로 규모가 작아 체계적인 안전관리가 이루어지지 않거나 경과연수가 50년 이상인 필댐(fill dam) 형식으로 축조된 노후저수지로서 갑작스러운 홍수를 대응하는데 있어 매우 취약한 상태이다. 체계적으로 운영되는 대형댐에 비해 축조기간이 오래된 소규모 저수지의 경우, 저수지에 대한 수문학적 정보가 거의 없거나 미계측되어 보수보강이 필요한 저수지를 선정하거나 정량적인 위험도를 분석하는데 매우 어려운 실정이다. 이러한 이유로 본 연구에서는 노후된 소규모 저수지에 대한 수문학적 파괴인자들을 선정하여 Bayesian Network기반의 소규모 저수지 위험도 분석 모형을 구축하였다. 구축된 모형을 기준으로 고려될 수 있는 다양한 위험인자 및 이들 인자간의 연관성을 평가하였으며, 각각의 노드에 파괴인자를 노드로 할당하여 소규모 저수지의 위험도를 분석하였다. Bayesian Network기법의 도입으로 불확실한 상황을 확률로 표시하고, 복잡한 추론을 정량화된 노드의 관계로 단순화시켜 노드의 연결 관계로 표현하였다. 본 연구에서 제안된 모형은 노후된 소규모 저수지의 수문학적 위험도를 정량으로 분석하는 모형으로서 활용성이 높을 것으로 기대된다.

• The KIPS Transactions:PartA
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• v.16A no.3
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• pp.169-180
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• 2009

With fixed sinks, the network stability could be improved while the network life time could be decreased by the rapid energy dissipation around the fixed sink because of the concentrated network traffic from sensor nodes to the fixed sink in wireless sensor network. To address this problem, mobile sinks, which decentralize the network traffic, has received a lot of attention from many researchers recently. Since a mobile sink has a limited period to communicate with each sensor nodes, it is necessary for a scheduling algorithm to provide the fairness of data collection from each sensor nodes. In the paper, we propose the new scheduling algorithm, ASF(Availability based Scheduling scheme for Fair data collection), for the fair data collection by a mobile in the sensor networks. The ASF takes account of the distance between each sensor nodes and the mobile sink as scheduling metric, as well as the amount of collected data from each sensor nodes. Experiment results shows that the ASF improves the fairness of data collection among the sensor nodes, comparing to existing algorithm.

• Journal of the Korean Institute of Intelligent Systems
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• v.23 no.6
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• pp.558-564
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• 2013

Wireless sensor networks (WSNs) contain limited energy resources and are left in open environments. Since these sensor nodes are self-operated, attacks such as sinkhole attacks are possible as they can be compromised by an adversary. The sinkhole attack may cause to change initially constructed routing paths, and capture of significant information at the compromised node. A localized encryption and authentication protocol (LEAP) has been proposed to authenticate packets and node states by using four types of keys against the sinkhole attack. Even though this novel approach can securely transmits the packets to a base station, the packets are forwarded along the constructed paths without checking the next hop node states. In this paper, we propose the next hop node selection method to cater this problem. Our proposed method evaluates the next hop node considering three factors (i.e., remaining energy level, number of shared keys, and number of filtered false packets). When the suitability criterion for next hop node selection is satisfied against a fix threshold value, the packet is forwarded to the next hop node. We aim to enhance energy efficiency and a detour of attacked areas to be effectively selected Experimental results demonstrate validity of the proposed method with up to 6% energy saving against the sinkhole attack as compared to the LEAP.

• Journal of Korea Society of Industrial Information Systems
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• v.9 no.4
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• pp.90-98
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• 2004

This paper covers the issue of securing ad hoc networks. Such networks exhibit a number of characteristics that make such a task challenging. One of the major challenges is that ad hoc networks typically lack a fixed infrastructure both in form of physical infrastructure such as routers, servers, and stable communication links and in the form of an organizational or administrative infrastructure. Another difficulty lies in the highly dynamic nature of ad hoc networks since new nodes can join and leave the network at any time. The major problem in providing security services in such infrastructure less networks is how to manage the cryptographic keys that are needed. In order to design practical and efficient key management systems it is necessary to understand the characteristics of ad hoc networks and why traditional key management systems cannot be used. These issues are covered and we also present a new efficient key management solutions. Finally we show that the proposed method is more efficient than the previous works through simulations.

• Journal of KIISE:Databases
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• v.35 no.3
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• pp.208-217
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• 2008

Sensors have a function to gather environment-related information operating by small-size battery in sensor networks. The issue related with energy is still an important in spite of the recent advancements in micro-electro-mechanical-system(MEMS) related techology. Generally it is assumed that replacement or rechargement of battery power in sensor is not feasible and a message send operation may spend at least 1000 times battery than a local operation. Thus, there have been several kinds of research efforts to lessen the number of unnecessary messages by maintaining the information of the other neighboring(or all) sensors. In this paper, we propose an index structure based on parent-children relationship to the purpose. Namely, parent node gathers the set of location information and MBA per child. It's named PH and may allow to process the range query with higher accurate and small size information. Through extensive experiments, we show that our index structure has better energy consumption.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.9
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• pp.2143-2149
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• 2010

An agent based geographic routing protocol is proposed to improve the well-known geographic routing protocol-GPSR routing protocol. In the proposed scheme, the agent is selected by sink node which concern about the source node's position as well as agent candidate's state. So packets will first be forwarded to agent and next step is to be forwarded to their final goal- sink node from agent. During the next hop selection process, nodes select their neighbors by considering not only position but also their average available buffer size. This results in efficient selection of next hop node in congestion area, and then increases the successful packet delivery ratio. The simulation is conducted for two scenarios: general number of connections and large number of connections in our map. Results show that new method with agent achieves improved performance in successful packet delivery ratio when compares to GPSR without our scheme.

• The Journal of the Korea Contents Association
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• v.10 no.4
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• pp.55-65
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• 2010

We present a method for increasing network lifetime without link failure due to lack of battery capacity of nodes in wireless ad-hoc networks with low mobility. In general, a node with larger remaining battery capacity represents the one with lesser traffic load. Thus, a modified AODV routing protocol is proposed to determine a possible route by considering a remaining battery capacity of a node. Besides, the total energy consumption of all nodes increase rapidly due to the huge amount of control packets which should be flooded into the network. To reduce such control packets efficiently, a source node can store information about alternative routes to the destination node into its routing table. When a link failure happens, the source node should retrieve the route first with the largest amount of the total remaining battery capacity from its table entries before initiating the route rediscovery process. To do so, the possibility of generating unnecessary AODV control packets should be reduced. The method proposed in this paper increases the network lifetime by 40% at most compared with the legacy AODV and MMBCR.

• Journal of the Korean Institute of Intelligent Systems
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• v.16 no.6
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• pp.777-784
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• 2006

This paper proposes a c-fuzzy model tree using partial least square method to predict the Chlorophyll-a concentration in each zone. First, cluster centers are calculated by fuzzy clustering method using all input and output attributes. And then, each internal node is produced according to fuzzy membership values between centers and input attributes. Linear models are constructed by partial least square method considering input-output pairs remained in each internal node. The expansion of internal node is determined by comparing errors calculated in parent node with ones in child node, respectively. On the other hands, prediction is performed with a linear model haying the highest fuzzy membership value between input attributes and cluster centers in leaf nodes. To show the effectiveness of the proposed method, we have applied our method to water quality data set measured at several stations. Under various experiments, our proposed method shows better performance than conventional least square based model tree method.

• Annual Conference of KIPS
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• 2010.11a
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• pp.913-916
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• 2010

Wireless sensor networks consist of small battery powered devices with limited energy resources. Once deployed, the small sensor nodes are usually inaccessible to the user, and thus replacement of the energy source is not feasible. Hence, energy efficiency is a key design issue that needs to be enhanced in order to improve the life span of the network. In BCDCP, all sensors send data from CH (Cluster Head) and then to BS (Base Station). BCDCP works well in small-scale network but in large scale network it is not appropriated since it uses much energy for long distance wireless communication. We propose a routing protocol - Triangular Clustering Routing Protocol (TCRP) - to prolong network life time through the balanced energy consumption. TCRP selects cluster head of triangular shape. The sensor field is divided into energy level and in every level we choose one node as a gate node. This gate node collects data and sends it to the leader node. Finally the leader node sends the aggregated data to the BS. We show TCRP outperforms BCDCP with several experiments.