• Journal of KIISE
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• v.43 no.12
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• pp.1428-1436
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• 2016

A multipath routing in wireless sensor networks (WSNs) provides advantage such as reliability improvement and load balancing by transmitting data through divided paths. For these reasons, existing multipath routing protocols divide path appropriately or create independent paths efficiently. However, when the sink node moves to avoid hotspot problem or satisfy the requirement of the applications, the existing protocols have to reconstruct multipath or exploit foot-print chaining mechanism. As a result, the existing protocols will shorten the lifetime of a network due to excessive energy consumption, and lose the advantage of multipath routing due to the merging of paths. To solve this problem, we propose a multipath creation and maintenance scheme to support the mobile sink node. The proposed protocol can be used to construct local grid structure with restricted area and exploit grid structure for constructing the multipath. The grid structure can also be extended depending on the movement of the sink node. In addition, the multipath can be partially reconstructed to prevent merging paths. Simulation results show that the proposed protocol is superior to the existing protocols in terms of energy efficiency and packet delivery ratio.

• Journal of KIISE:Information Networking
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• v.36 no.3
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• pp.222-230
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• 2009

A sensor network is an important element of the ubiquitous and it consists of sensor fields that contain sensor nodes and sink nodes that collect data from sensor nodes. Since each sensor node has limited resources, one of the important issues covered in the past sensor network studies has been maximizing the usage of limited energy to extend network lifetime. However, most studies have only considered fixed sink nodes, which created various problems for cases with multiple mobile sink nodes. Accordingly, while maintaining routes to mobile sink nodes, this study aims to deploy the hybrid communication mode that combines single and multi-hop modes for intra-cluster and inter-cluster transmission to resolve the problem of failed data transmission to mobile sink nodes caused by disconnected routes. Furthermore, a 2-level hierarchical routing protocol was used to reduce the number of sensor nodes participating in data transmission, and cross-shape trajectory forwarding was employed in packet transmission to provide an efficient data dissemination method.

• Journal of Convergence Society for SMB
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• v.6 no.4
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• pp.37-43
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• 2016

Sinkholes happen in increasingly higher frequency in downtown areas with a concentration of social infrastructure these days. Most sinkholes occur around the living areas of citizens, which calls for a systematic countermeasure plan for urban development and underground water management, which are parts of the main causes of sinkholes. This study thus set out to analyze the risk factors of sinkholes in the subject area by using geospatial information deeply connected to sinkholes both directly and indirectly. The geospatial information used in analysis was obtained by examining the causes of sinkholes from a topographical perspective. Collected data were treated and analyzed with a range of spatial analysis tools based on GIS. The findings show that topographical factors had significant relations with sinkhole causes and raise a need to manage all kinds of pipe networks underground, the movement characteristics of underground water levels, and other topographical features. The findings may serve as data to support decision-making processes in the field of urban disaster prevention and call for extensive research to incorporate hydro-geomorphology and spatial modeling.

• The KIPS Transactions:PartC
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• v.15C no.5
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• pp.383-390
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• 2008

The mobile sink is most suitable to guarantee the real time processing to events in ubiquitous environment. However it brings many challenges to wireless sensor networks. In particular, the question of how to transfer the collected data to the mobile sink is an important topic in the aspect of effective management of wireless sensor nodes. In this paper, a new data dissemination model is proposed. Since this method uses the home agent and the access node concepts, it provides reliable and efficient data delivery to mobile sink with minimum overhead. In this proposed method, the information of the mobile sink which is constantly moving is informed only to the home agent node and the access node, instead of all sensor nodes. Thus, the collected data from sensor nodes are transferred to the fixed home agent and it sends these data to the mobile sink. Since the confliction phenomenon between data packets in wireless networks could be reduced, the success ratio of data arriving in the mobile sink is highly enhanced. In our experiments, the proposed method reduces the number of broadcast packets so that it saves the amount of energy consumed for transmitting and receiving the data packets. This effect contributes to prolong the lifetime of the wireless sensor networks operated by batteries.

• KIPS Transactions on Computer and Communication Systems
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• v.5 no.11
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• pp.385-392
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• 2016

Recently, Expectation Area-based Real-time Routing (EAR2) protocol has been proposed to support real-time routing in wireless sensor networks. EAR2 considers the expectation area of a mobile sink and uses flooding within the expectation area. However, flooding leads to excessive energy consumption and causes long delay against real-time routing. Moreover, since EAR2 uses single path to the expectation area, it is difficult to support reliable routing in sensor networks with high link failures. Thus, to overcome these limitation of EAR2, this paper proposes a reliable and real-time routing protocol based on virtual grids and multipath for mobile sinks. To support real-time routing, the proposed protocol considers expectation grids belonged to the expectation area. Instead of flooding within the expectation area, the proposed protocol uses multicasting to the expectation grids and single hop forwarding in an expectation grid because the multicasting can save much energy and the single hop forwarding can provide short delay. Also, the proposed protocol uses multipath to the expectation grids to deal with link failures for supporting reliable routing. Simulation results show that the proposed protocol is superior to the existing protocols.

• KIPS Transactions on Computer and Communication Systems
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• v.9 no.4
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• pp.77-82
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• 2020

Wireless sensor networks (WSNs) suffer from not only a short lifetime due to limited energy but also an energy imbalance between nodes close to the sink and others. In order to fundamentally solve the short lifetime, recent studies utilize the environmental energy such as solar power. Additionally, WSNs using mobile sinks are being studied to address the energy imbalance problem. This paper proposes an improved CTP (Collection Tree Protocol) scheme which uses these two approaches simultaneously. Basically, it is based on a CTP scheme which is a very popular data collection strategy designed for the typical battery-based WSNs with a fixed sink. Therefore, we tailored it for solar-powered WSNs with a mobile sink. Performance verification confirms that our scheme reduces the number of blackout nodes significantly compared to the typical CTP, thus increases the amount of data collected by the sink.

• Proceedings of the Korean Society of Computer Information Conference
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• 2014.07a
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• pp.55-56
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• 2014

모바일 장치의 대중화와 이동 통신 기술의 발전이 가속화 되면서, 최근 모바일 봇넷으로 인한 위협이 증가하고 있다. 봇넷의 안정적인 유지와 봇 마스터와 클라이언트 간 통신 채널의 은닉성을 보장하기 위해 다양한 방법이 연구되었다. 본 논문에서는 모바일 환경에서 널리 사용되는 클라우드 기반의 파일 싱크 서비스를 통신 채널로 활용한 새로운 봇넷을 제안한다. 안드로이드 플랫폼 기반의 봇 클라이언트 구현과 실험을 통해 제안하는 봇넷이 사용하는 C&C 채널의 은닉성을 검증하고 공격의 심각성을 보였다.

• Proceedings of the Korean Society of Computer Information Conference
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• 2015.01a
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• pp.225-226
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• 2015

본 논문은 PMIPv6 기반 무선 네트워크 환경에서 입체영상을 송수신하는 멀티인터페이스 이동노드의 핸드오버 수행 시 손실을 최소화하기 위한 MPTCP 기반의 입체영상 전송기법을 제안하다. 제안하는 입체영상 전송 기법은 입체영상 단말 이동 시 멀티인터페이스 간 입체영상으로 정의된 플로우의 플로우 이동성이 수행되며 플로우 이동성 발생 시 단대단 연결 단절 현상을 MPTCP Sublflow 기능을 통해 극복한다. 기존 기법에 비해 제안하는 기법은 데이터 손실 및 단대단 지연을 최소화하며 이동성 환경에서 입체영상의 좌우영상 싱크문제를 극복하는 방법이다.

• Proceedings of the Korean Information Science Society Conference
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• 2005.11a
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• pp.187-189
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• 2005

무선 센서네트워크는 다수의 센서 노드로 구성되어 데이터를 수집하는 네트워크다. 센서 네트워크를 이루는 노드는 대부분 이동성이 없는 고정식 노드이다. 그러나 현재 센서 네트워크의 다양한 응용의 확장은 이동성있는 모바일 센서노드에 대한 지원을 요구하고 있다. 본 논문에서는 이동성 있는 모바일 센서 노드의 네트워크 구성과 데이터 전송을 위해 셀을 기반으로 센서네트워크를 구성하고, 셀의 헤드를 이용하여 이동성 노드로부터 싱크 노드로의 데이터 전송이 가능하도록 무선 센서네트워크의 자기 구성 알고리즘을 제안하였다.

• The Transactions of the Korean Institute of Power Electronics
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• v.13 no.4
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• pp.311-318
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• 2008

This paper proposes synchronous bidirectional DC-DC converter applying soft-switching technique. The proposed converter integrates two advantages which are conduction loss minimization and switching loss elimination by applying interleaved synchronous buck and ZVT-cell with a single resonant inductor. ZVS is guaranteed for wide load range in CCM(Continuous Conduction Mode) as well as wide output voltage range by current injection method. Also, reverse recovery effects of body diode can be minimized. In addition, it is possible to significantly reduce diode drop voltage occurred during dead time of conventional synchronous buck converter. The validity of the proposed converter is verified through experimental results.