• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.6
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• pp.109-116
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• 2007

The lack of load-balancing functionality in most existing ad hoc routing protocols often causes congestion resulting in bad performance and short lifetime of participating nodes. We present an auxiliary scheme for reactive routing protocols to discover an unloaded route, thereby decreasing possibility of congestion. The scheme allows an intermediate node to determine whether to be a relaying node for a newly constructed route autonomously based on the occupancy of its queue. Thus the scheme does not require network-wide load information. Simulation results show that the proposed scheme distributes traffic load well.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.42 no.1
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• pp.87-94
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• 2019

A wireless sensor network is emerging technology and intelligent wireless communication paradigm that is dynamically aware of its surrounding environment. It is also able to respond to it in order to achieve reliable and efficient communication. The dynamical cognition capability and environmental adaptability rely on organizing dynamical networks effectively. However, optimally clustering the cognitive wireless sensor networks is an NP-complete problem. The objective of this paper is to develop an optimal sensor network design for maximizing the performance. This proposed Ranking Artificial Bee Colony (RABC) is developed based on Artificial Bee Colony (ABC) with ranking strategy. The ranking strategy can make the much better solutions by combining the best solutions so far and add these solutions in the solution population when applying ABC. RABC is designed to adapt to topological changes to any network graph in a time. We can minimize the total energy dissipation of sensors to prolong the lifetime of a network to balance the energy consumption of all nodes with robust optimal solution. Simulation results show that the performance of our proposed RABC is better than those of previous methods (LEACH, LEACH-C, and etc.) in wireless sensor networks. Our proposed method is the best for the 100 node-network example when the Sink node is centrally located.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.16 no.5
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• pp.25-34
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• 2006

Previous binding update protocols for Mobile IPv6 repeats the same protocol each time a mobile node moves to a foreign link Moreover, mobile nodes repeats the same protocol whenever the lifetime of the current binding update expires. To improve the efficiency of binding updates, we Propose a ticket-based binding update protocol for MIPv6. Our protocol minimizes the binding update cost using a ticket issued by the corresponding node. We have analyzed our protocol security against the security requirements of MIPv6 and existing attacks. Furthermore, we have also compared our protocol against previous binding update protocols.

• International Journal of Computer Science & Network Security
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• v.21 no.1
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• pp.6-11
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• 2021

Routing protocols play a pivotal role in the energy management and lifespan of any Wireless Sensor Network. Lower network lifetime has been one of the biggest concerns in LEACH protocol due to dead nodes. The LEACH protocol suffers from uneven energy distribution problem due to random selection of a cluster head. The cluster head has much greater responsibility compared to other non- cluster head nodes and consumes greater energy for its roles. This results in early dead nodes due to energy lost for the role of cluster- head. This study proposes an approach to balance the energy consumption of the LEACH protocol by using a semi-deterministic opportunity coefficient to select the cluster head. This is calculated in each node with the battery energy level and node ID. Ultimately, based on the opportunity cost, cluster head will be selected and broadcasted for which other nodes with higher opportunity cost will agree. It minimizes the chances of nodes with lower battery level being elected as cluster head. Our simulation experiments demonstrate that cluster heads chosen using our proposed algorithm perform better than those using the legacy LEACH protocol.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.9
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• pp.3472-3480
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• 2010

The Clustering technology of Energy efficiency wireless sensor network gets the energy efficiency by reducing the number of communication between sensor nodes and sink node. In this paper, First analyzed on the clustering technique of the distributed clustering protocol routing scheme LEACH (Low Energy Adaptive Clustering Hierarchy) and HEED (Hybrid, Energy-Efficient Distributed Clustering Approach), and based on this, new energy-efficient clustering technique is proposed for the cause the maximum delay of dead nodes and to increase the lifetime of the network. In the proposed method, the cluster head is elect the optimal efficiency node based on the residual energy information of each member node and located information between sink node and cluster node, and elected a node in the cluster head since the data transfer process from the data been sent to the sink node to form a network by sending the energy consumption of individual nodes evenly to increase the network's entire life is the purpose of this study. To verify the performance of the proposed method through simulation and compared with existing clustering techniques. As a result, compared to the existing method of the network life cycle is approximately 5-10% improvement could be confirmed.

• Korean Journal of Head & Neck Oncology
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• v.35 no.2
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• pp.11-17
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• 2019

Background/Objectives: Papillary thyroid carcinoma (PTC) has generally an indolent character with a good prognosis. However, recurrence remains a major concern for the patients during their lifetime. Despite the slowly progressing character of PTC, recurrence can occur within a short period after initial surgery. This study aimed to determine the clinical findings and cause of recurrence in patients who underwent re-operative surgery due to neck node recurrence by reviewing the CT (computed tomographic) scan imaging of the recurrence of PTC retrospectively. Materials & Methods: We reviewed the medical records of patients referred to Ajou University Hospital from January 2002 to January 2018. All patients had re-operative surgery due to neck node recurrence and CT scan results of preoperative evaluation and postoperative follow up. Over this period, 110 patients who underwent re-operation due to neck node recurrence with a CT scan were included in our cohort, resulting in a total of 220 re-operations. Results: The time from initial operation to first re-operation was examined in 110 patients. The median time to re-operation was 28 months, with a range of 4 months to 186 months. Most re-operations (82.7%) occurred within the first five years, 43.6% were in the first two years from the initial surgery. The result of the retrospective CT review showed newly developed cases (21,19.1%), missed diagnosis cases (42,38.2%), real recur cases after surgery (33,30.0%), and remnant lymph nodes (LNs) cases (14,12.7%). We further sub-analyzed 14 cases with remnant LNs. Reasons for remnant LNs included insufficient operation (N=5) and beyond general surgical extent. (N=9). Conclusion: Re-operation due to cervical lymph node recurrence is mostly a persistent disease. They included a missed diagnosis and incomplete operation. These finding may reduce the reoperation of cervical lymph node recurrence by accurate preoperative evaluation and complete surgical resection at the initial surgery.

• Journal of KIISE:Information Networking
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• v.36 no.4
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• pp.339-350
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• 2009

In wireless sensor networks, the limited battery resources of sensor nodes have a direct impact on network lifetime. To reduce unnecessary power consumption, it is often the case that only a minimum number of sensor nodes operate in active mode while the others are kept in sleep mode. In such a case, however, the network service can be easily unreliable if any active node is unable to perform its sensing or communication function because of an unexpected failure. Thus, for achieving reliable sensing, it is important to maintain the sensing level even when some sensor nodes fail. In this paper, we propose a new fault-tolerance scheme, called FCP(Fault-tolerant Coverage Preserving), that gives an efficient way to handle the degradation of the sensing level caused by sensor node failures. In the proposed FCP scheme, a set of backup nodes are pre-designated for each active node to be used to replace the active node in case of its failure. Experimental results show that the FCP scheme provides enhanced performance with reduced overhead in terms of sensing coverage preserving, the number of backup nodes and the amount of control messages. On the average, the percentage of coverage preserving is improved by 87.2% while the additional number of backup nodes and the additional amount of control messages are reduced by 57.6% and 99.5%, respectively, compared with previous fault-tolerance schemes.

• The KIPS Transactions:PartC
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• v.16C no.6
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• pp.731-736
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• 2009

In wireless sensor network, many sensor nodes are distributed in the field. They communicate the sensing data each other and forward it to sink. Routing protocols, which define the delivery methods of sending data, affect to the lifetime of sensor network. This paper proposes RTAF that is a routing-tree construction algorithm of sensor nodes by a single flooding process in wireless sensor network. A routing tree is constructed by selecting a parent node using the forward-direction flooding packet and gathering children nodes using the reverse-direction flooding packet. In this process, a node with much energy becomes the parent node. And the routing tree is periodically reconstructed in order to distribute the loads of parent nodes. The proposed algorithm compared performance with Modified-LEACH using NS2 network simulation tool. The simulation result shows that the proposed algorithm constructs a routing-tree faster and reduced 40-80% in routing-tree construction packet.

• Journal of information and communication convergence engineering
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• v.6 no.2
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• pp.117-121
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• 2008

In ad hoc network, the scarce energy management of the mobile devices has become a critical issue in order to extend the network lifetime. Therefore, the energy consumption is important in the routing design, otherwise cluster schemes are efficient in energy conserving. For the above reasons, an Energy conserving Context aware Clustering algorithm (ECC) is proposed to establish the network clustering structure, and a routing algorithm is introduced to choose the Optimal Energy Routing Protocol (OERP) path in this paper. Because in ad hoc network, the topology, nodes residual energy and energy consuming rate are dynamic changing. The network system should react continuously and rapidly to the changing conditions, and make corresponding action according different conditions. So we use the context aware computing to actualize the cluster head node, the routing path choosing. In this paper, we consider a novel routing protocol using the cluster schemes to find the optimal energy routing path based on a special topology structure of Resilient Ontology Multicasting Routing Protocol (RODMRP). The RODMRP is one of the hierarchical ad hoc network structure which combines the advantage of the tree based and the mesh based network. This scheme divides the nodes in different level found on the node energy condition, and the clustering is established based on the levels. This protocol considered the residual energy of the nodes and the total consuming energy ratio on the routing path to get the energy efficiently routing. The proposed networks scheme could get better improve the awareness for data to achieve and performance on their clustering establishment and messages transmission. Also, by using the context aware computing, according to the condition and the rules defined, the sensor nodes could adjust their behaviors correspondingly to improve the network routing.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.10B
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• pp.981-987
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• 2009

Recently, the study on wireless body area network for providing ubiquitous healthcare services has been actively done, including the standardization of the IEEE and others. Wireless body area network is usually configured in tree format using multi-hop communication mode due to the power limitation and the characteristics of human body. In this case, differently from existing sensor network, the wireless body area network tends to be disconnected due to the frequent movement of human body. The number of connections which can be supported at each node has some limitations due to the constraint imposed on power consumption. In this paper, we have proposed a heuristic algorithm for optimal selection of parent node with guaranteed QoS for a disconnected node, which considers the priority on packet transmission. Simulation has been performed to evaluate the performance of the proposed algorithm.