• The Journal of the Korea Contents Association
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• v.13 no.2
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• pp.52-61
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• 2013

In wireless sensor networks, the geographical positioning scheme is one of core technologies for sensor applications such as disaster monitoring and environment monitoring. For this reason, studies on range-free positioning schemes have been actively progressing. The density probability scheme based on central limit theorem and normal distribution was proposed to improve the location accuracy in non-uniform sensor network environments. The density probability scheme measures the final positions of unknown nodes by estimating distance through the sensor node communication. However, it has a problem that all of the neighboring nodes have the same 1-hop distance. In this paper, we propose an efficient sensor positioning scheme that overcomes this problem. The proposed scheme performs the second positioning step through the sensing range control after estimating the 1-hop distance of each node in order to minimize the estimation error. Our experimental results show that our proposed scheme improves the accuracy of sensor positioning by about 9% over the density probability scheme and by about 48% over the DV-HOP scheme.

• Smart Media Journal
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• v.9 no.3
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• pp.71-79
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• 2020

Mobile network is used by many users worldwide for diverse services, including phone-call, messaging and data transfer over the Internet. However, this network may experience massive damage if it is exposed to cyber-attacks or denial-of-service attacks via wireless communication interference. Because the mobile network is also used as an emergency network in cases of disaster, evaluation or verification for security and safety is necessary as an important nation-wide asset. However, it is not easy to analyze the mobile core network because it's built and serviced by private service providers, exclusively operated, and there is even no separate network for testing. Thus, in this paper, a virtual mobile network is built using OpenAirInterface, which is implemented based on 3GPP standards and provided as an open source software, and the structure and protocols of the core network are analyzed. In particular, the S1AP protocol messages captured on S1-MME, the interface between the base station eNodeB and the mobility manager MME, are analyzed to identify potential security threats by evaluating the effect of the messages sent from the user terminal UE to the mobile core network.

• Journal of KIISE:Information Networking
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• v.32 no.6
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• pp.745-752
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• 2005

BGP is a unique routing protocol in broadband internet. It chooses routing paths considering internet hierarchy and local policies. As BGP routers selectively bypass routing information to a subset of neighboring BGP routers, connectivity by way of a series of links between source and destination nodes does not mean reachability of routing information of the two. In emergency when BGP routers or links over wide range are not available, BGP routers have to use links that are not normally used to keep reachability. This paper listed out the requirements for BGP backup routing and proposed a routing solution that hides most demerits in currently published ones. The proposed backup operates in three tiers according to network damage. Under this rule, BGP routers use tier-0 routing paths at normal. If networks are impaired, they choose tier-1 paths. If networks are seriously damaged, tier-2 paths are allowed to use. Also this paper proves that the proposed backup guarantees stability and safeness. As results, the proposed backup is very adaptive to light network damages as well as serious ones and provides strong routing reachability at all times.

• Journal of Digital Contents Society
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• v.19 no.5
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• pp.963-969
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• 2018

Wi-Fi and Bluetooth technologies are perhaps the most prominent examples of wireless communication technologies used in the Internet of Things (IoT) environment. Compared to widely used Wi-Fi, Bluetooth technology has some flaws including 1:1 connection (one-way) between Master and Slave, slow transmission, and limited connection range; Bluetooth is mainly used for connecting audio devices. Since the release of Bluetooth Low Energy (BLE), some of the flaws of Bluetooth technology have been improved but it still failed to become a competitive alternative of Wi-Fi. This paper presents a method of data transmission through broadcasting in BLE and demonstrates its performance, one-to-many data transfer result. The Connection-Free Data Transmission proposed in this paper will hopefully be utilized in special circumstances requiring 1:N data transmission or disaster security network.

• Journal of the Korean Association of Geographic Information Studies
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• v.10 no.2
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• pp.172-183
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• 2007

Recently geospatial information has used widely in many areas such as effective use and management of national land, establishment of city planning, managements of environments and disasters, etc. But present digital map is not suitable for nowadays because of delay of information renewal and changes of topography. In this study, GIS DB construction method was researched through the process of extracting main vector layers such as buildings, roads, contours, etc. from LiDAR data. In order to analyze accuracies of constructed data, the digital topographic maps of 1:1000 scale which were produced by Korea National Geographic Information Institute(NGI) and results of GPS survey were used. Effective DB construction method was suggested through comparing with existing GIS DB construction methods.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.8
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• pp.976-984
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• 2012

Ad hoc networks can be used under difficult conditions, where it is difficult to construct infrastructures, such as shadowing areas, disaster areas, war area, and so on. In order to support to considerable and various wireless services, more spectrum resources are needed. However, efficient utilization of the frequency resource is difficult because of spectrum scarcity and the conventional frequency regulation. Ad-hoc networks employing cognitive radio(CR) system that guarantee high spectrum utilization provide effective way to increase the network capacity. However, there is a problem that all CR user do not fairly use the primary user's idle bandwidth which has been sensed. In this paper, to solve this problem, we propose the spectrum sharing algorithm which uses the multiple orthogonal sequences based on the code division multiple access(CDMA). From the proposed algorithm, it is expected that system performance of CR based ad-hoc network is improved significantly and it can be applied to the implementation of CR based ad-hoc network system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.5
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• pp.632-639
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• 2012

Ad-hoc networks can be used various environment, which it is difficult to construct infrastructures, such as shadowing areas, disaster areas, war area, and so on. In order to support to considerable and various wireless services, more spectrum resources are needed. However, efficient utilization of the frequency resource is difficult because of spectrum scarcity and the conventional frequency regulation. Ad-hoc networks employing cognitive radio(CR) system that guarantee high spectrum utilization provide effective way to increase the network capacity. In conventional CR based ad-hoc network, it uses constant threshold value to detect primary user signal, so the results become not reliable. In this paper, to solve this problem, we apply adaptive threshold value to the CR based ad-hoc network, and adaptive threshold is immediately changed by SNR(Signal to Noise Ratio). From the simulation results, we confirmed that proposed algorithm has the greatly better detection probabilities than conventional CR based ad-hoc network.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.2
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• pp.175-181
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• 2006

Wireless sensor network forms the self-organization network, and transfers the information among sensor nodes that have computing technology ability and wireless communication ability. The recent sensor network is study for low-power, micro, low cost of node is proceeded. Recently, the research of application services in wireless sensor networks is proceeded. Therefore, in this paper, we design the prototype of the real-time information service that support a user the information of temperature, illumination etc. And, we implement the alarm application service fer the disaster prevention on Internet base on IPv4/IPv6. We develop the module of the extract information using the query processing based on TinyOS, and the module of the server's database using MySQL data base management system and JDBC. Additionally, we develop the client module that receive the real-time sensing data using ODBC in Internet based on IPv4/IPv6.

• Journal of KIISE:Computing Practices and Letters
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• v.16 no.1
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• pp.80-84
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• 2010

Data multicasting from a source to multiple sinks in wireless sensor networks is used to achieve both reducing communication costs and energy efficiency. Almost all existing schemes for the multicasting might be effectively performed by optimal construction of a multicasting tree between a source and multiple stationary sinks. However, in practical sensor applications, sinks could move around on the wireless sensor networks for own missions, such as scouting of soldiers and saving lives of victims by firefighters. Unfortunately, the sink mobility causes frequent entire reconstruction of the multicasting tree and thus it leads to exhaustion of battery power of sensors. Hence, we propose an energy-efficient multicast protocol to support multiple mobile sinks by the local multicast tree reconstruction, called Local Update-based geographic Multicasting for Mobile sinks (LUMM) for wireless sensor networks. Our simulation results show that our scheme for mobile sinks is more efficient in terms of energy resource management than other exist works.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.77-77
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• 2015

기상이변으로 인한 사회 경제적 피해의 증가로 기상정보에 대한 중요성이 커지면서 해외에서는 민간 기업이 기상 관측망을 구축하는 사례가 나타났다. 미국의 Earth Network은 전 세계에 1만개의 기상 관측센서를 설치하였고, 일본의 통신회사인 NTT DoCoMo는 일본에 4000여 개의 기상 및 환경관측 센서를 구축하였다. 국내에서는 SK플래닛이 자사의 플랫폼 기술과 SK텔레콤의 기지국 인프라를 활용하여 수도권 지역에 국지기상 관측망을 구축하였다. SK플래닛은 2013년 서울지역에 1km 간격으로 264개의 기상센서를 설치하고, 2014년 인천 경기지역에 3km 간격으로 825개의 기상센서를 추가 설치하여, 현재 1089개의 국지기상 관측망을 운용하고 있다. 관측에 사용한 센서는 우량계와 복합 기상센서로 강수량, 기온, 습도, 바람, 기압을 측정한다. 관측된 자료는 데이터로거에서 기상청의 자료처리 표준규격에 따라 처리한 후 M2M 모뎀을 통해 1분마다 서버로 전송한다. 전송된 자료는 기상정보 플랫폼의 수집 서버에서 프로토콜 변환 후 원본자료 DB에 저장하고, 실시간 품질관리를 마친 후 품질관리 자료 DB에 저장한다. 관측 지점의 기본정보 및 작업이력은 메타데이터 DB에 저장되고 관리자 페이지를 통해 조회 및 수정 된다. 관측 자료의 품질 보증은 제조사의 센서 Calibration부터 서비스 모니터링 까지 각 단계별로 체계적인 품질관리를 통해 이루어진다. 품질관리를 마친 국지기상 관측 데이터는 응용프로그램 개발자가 편리하게 사용할 수 있는 API(Application Programming Interface)형태로 제공된다. 2013년 여름부터 수집된 1~3km 해상도의 SK플래닛 국지기상 관측 자료를 통해 그 동안 정량적으로 확인하지 못한 국지성 호우 시의 강수량 편차에 대해 알 수 있었다. 2014년 7월 31일 양평지역에 내린 국지성 호우는 시간당 최대 90mm 이상의 비가 내린 사례로, 귀여리 관측소(SK 플래닛)에 시간당 93.1mm가 내리는 동안 퇴촌 관측소(기상청)에는 17.5mm의 비가 내려, 두 관측지점 간 거리가 3.4km 임에도 불구하고 시간당 75mm 이상의 강수량 차이를 보였다. 앞으로 SK플래닛의 국지기상 관측 자료가 국지성 호우의 조기 경보 및 예측 정확도 향상에 활용되어 재난으로부터 국민의 생명과 재산을 지키는데 많은 도움이 되기를 기대한다.