• Journal of the Korean Institute of Telematics and Electronics B
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• v.30B no.1
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• pp.10-17
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• 1993

This paper analyzes succinct graph descriptions and its complexity of connectivity problems on context free graph languages under various restrictions. It defines SNLC(Simple Context Free Node Label Controlled) grammar and presents reduction method that solves graph problems without expanding the hierarchical description. It exemplifies the method by giving efficient solutions to connectivity problems on graphs and presents parallel algorithm for reduction and analyzes the complexity. Its results will help application of desing for NETWORK. CAD. VLSI and other engineering problems.

• Proceedings of the Korean Society of Computer Information Conference
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• 2019.01a
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• pp.95-97
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• 2019

본 논문에서는 ZigBee 기반의 WSN과 노드 연결을 위한 새로운 기법을 제안한다. 이 기법은 통신 노드 간에 격리된 노드의 수를 최소화하기 위해 수신신호강도(RSSI) 샘플에 적용된 딕슨 테스트(Dixon's test)를 사용하여 ZigBee 기반의 WSN을 위한 새로운 노드 연결 구조로써 특이점(outlier)을 제거하여 적은 수의 RSSI 값으로도 정확한 노드 연결이 가능하다. 본 논문에서는 시뮬레이션을 통하여 제안하는 기법이 기존의 RSSI 기반의 기법보다 더 높은 정확도를 유지하면서 처리 시간은 줄어든 것을 증명하였다.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.27 no.4
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• pp.324-341
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• 2023

Topological data analysis (TDA) is a data analysis technique, recently developed, that investigates the overall shape of a given dataset. The mapper algorithm is a TDA method that considers the connectivity of the given data and converts the data into a mapper graph. Compared to persistent homology, another popular TDA tool, that mainly focuses on the homological structure of the given data, the mapper algorithm is more of a visualization method that represents the given data as a graph in a lower dimension. As it visualizes the overall data connectivity, it could be used as a prediction method that visualizes the new input points on the mapper graph. The existing mapper packages such as Giotto-TDA, Gudhi and Kepler Mapper provide the descriptive mapper algorithm, that is, the final output of those packages is mainly the mapper graph. In this paper, we develop a simple predictive algorithm. That is, the proposed algorithm identifies the node information within the established mapper graph associated with the new emerging data point. By checking the feature of the detected nodes, such as the anomality of the identified nodes, we can determine the feature of the new input data point. As an example, we employ the fraud credit card transaction data and provide an example that shows how the developed algorithm can be used as a node prediction method.

• Journal of Communications and Networks
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• v.16 no.2
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• pp.227-237
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• 2014

Throughput scaling laws for two coexisting ad hoc networks with m primary users (PUs) and n secondary users (SUs) randomly distributed in an unit area have been widely studied. Early work showed that the secondary network performs as well as stand-alone networks, namely, the per-node throughput of the secondary networks is ${\Theta}(1/\sqrt{n{\log}n})$. In this paper, we show that by exploiting directional spectrum opportunities in secondary network, the throughput of secondary network can be improved. If the beamwidth of secondary transmitter (TX)'s main lobe is ${\delta}=o(1/{\log}n)$, SUs can achieve a per-node throughput of ${\Theta}(1/\sqrt{n{\log}n})$ for directional transmission and omni reception (DTOR), which is ${\Theta}({\log}n)$ times higher than the throughput with-out directional transmission. On the contrary, if ${\delta}={\omega}(1/{\log}n)$, the throughput gain of SUs is $2{\pi}/{\delta}$ for DTOR compared with the throughput without directional antennas. Similarly, we have derived the throughput for other cases of directional transmission. The connectivity is another critical metric to evaluate the performance of random ad hoc networks. The relation between the number of SUs n and the number of PUs m is assumed to be $n=m^{\beta}$. We show that with the HDP-VDP routing scheme, which is widely employed in the analysis of throughput scaling laws of ad hoc networks, the connectivity of a single SU can be guaranteed when ${\beta}$ > 1, and the connectivity of a single secondary path can be guaranteed when ${\beta}$ > 2. While circumventing routing can improve the connectivity of cognitive radio ad hoc network, we verify that the connectivity of a single SU as well as a single secondary path can be guaranteed when ${\beta}$ > 1. Thus, to achieve the connectivity of secondary networks, the density of SUs should be (asymptotically) bigger than that of PUs.

• Journal of Sensor Science and Technology
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• v.16 no.4
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• pp.247-253
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• 2007

Low power consumption sensor network platform (sensor node) for sensor networking with IEEE 802.15.4 protocol was fabricated. The sensor node used ceramic bar type antenna for increasing RF signal performance and decreasing PCB size occupied by antenna. The communication range of the fabricated sensor node was about $20{\sim}30$ m in open environment with 915 MHz frequency bandwidth and well supported by Tiny OS. The sensor node have good connectivity with various external devices by RS-232, I2C, analogue and digital expansion board, hence, this sensor node can be applied to various applications in wireless sensor network and ubiquitous sensor network.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.8B
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• pp.657-667
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• 2012

In the MPR selection algorithm of Optimized Link State Routing (OLSR), each node selects own MPRs independently, so most of nodes are selected to MPR at least once. To cope with this problem, the MPR candidate selection algorithm was proposed. The MPR candidate selection algorithm can reduce the number of MPRs, but the efficiencies of route and connectivity decline due to decreased number of MPRs. So, in this paper, we propose the Significant Multi-Point Relay (S-MPR) selection algorithm which can enhance the performance of ad hoc network by improving the MPR selection algorithm of OLSR. In proposed S-MPR selection algorithm, each node selects the most important node to S-MPR to guarantee the connectivity then selects remaining MPRs in MPR candidates. So proposed S-MPR selection algorithm can reduce the overhead of many MPRs without decline of routing performance. To show the performance gain of proposed S-MPR selection algorithm, we simulate the proposed S-MPR selection algorithm by using OPNET.

• Journal of Korea Society of Industrial Information Systems
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• v.27 no.6
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• pp.41-49
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• 2022

The Internet Engineering Task Force (IETF) has standardized RPL (IPv6 Routing Protocol for Low-power Lossy Network) as a routing protocol for Low Power and Lossy Networks (LLNs), a low power loss network environment. RPL creates a route through an Objective Function (OF) suitable for the service required by LLNs and builds a Destination Oriented Directed Acyclic Graph (DODAG). Existing studies check the residual energy of each node and select a parent with the highest residual energy to build a DODAG, but the energy exhaustion of the parent can not avoid the network disconnection of the children nodes. Therefore, this paper proposes EC-RPL (Enhanced Connectivity-RPL), in which ta node leaves DODAG in advance when the remaining energy of the node falls below the specified energy threshold. The proposed protocol is implemented in Contiki, an open-source IoT operating system, and its performance is evaluated in Cooja simulator, and the number of control messages is compared using Foren6. Experimental results show that EC-RPL has 6.9% lower latency and 5.8% fewer control messages than the existing RPL, and the packet delivery rate is 1.7% higher.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.05a
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• pp.890-893
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• 2008

자율성 및 이동성 갖는 네트워크 구조의 하나인 MANET(Mobile Ad-Hoc Networks)은 각 node들은 그 특성에 따라서 clustering service을 한다. node의 전송과정 중 path access에 대하여 중요성 또한 강조되고 있다. 일반적인 무선 네트워크 상에서의 node들은 clustering을 하게 되는데 그 과정에서 발생되는 여러 가지 문제점을 가지고 전송이 이루어진다. 모든 node들이 송, 수신상의 전송 범위(Beam forming area)가지고 있으며, 이러한 각 node들의 전송범위 내에 전송이 이루어지는 전통적인 전송기술 mechanism을 찾는다. 이러한 전송상황에서의 송신하는 node와 수신된 node간에 발생되고 있는 중복성의 문제점으로 즉, 상호적용에 의한 네트워크 duplicate(overlapping)이 크게 우려가 되고 있다. 이러한 전송상의 전송 범위 중첩, node간의 packet 간섭현상, packet의 중복수신 및 broadcasting의 storming현상이 나타난다. 따라서 본 논문에서는 상황정보의 속성을 이용한 계층적 상호 head node들의 접근된 위치와 연계되는 전송속도, 보존하고 있는 head node들의 에너지 source value, doppler효과를 통한 head node의 이동방향 등 분석한다. 분석된 방법으로 전송상의 계층적 path가 구성된 경험적 path 속성을 통한 네트워크 connectivity 신뢰성을 극대화 할 뿐만 아니라 네트워크의 전송 범위 duplicate을 사전에 줄일 수 있고 전송망의 최적화를 유지할 수 있는 기법의 하나인 상황정보를 이용한 ad hoc network의 ODDMRP(Ontology Doppler effect-based Dynamic Multicast Routing Protocol) clustering 기법을 제안한다.

• Journal of the Korean Geographical Society
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• v.41 no.2 s.113
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• pp.188-194
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• 2006

Three-dimensional topological data is essential for 3D modeling and application such as emergency management and 3D network analysis. This paper reviewed current 3D topological data model and developed a method to construct 3D topological node-relation data structure from 2D computer aided design (CAD) data. The method needed two steps with medial axis-transformation and topological node-relation algorithms. Using a medial-axis transformation algorithm, the first step is to extract skeleton from wall data that was drawn polygon or double line in a CAD data. The second step is to build a topological node-relation structure by converting rooms to nodes and the relations between rooms to links. So, links represent adjacency and connectivity between nodes (rooms). As a result, with the conversion method 3D topological data for micro-level sub-unit of each building can be easily constructed from CAD data that are commonly used to design a building as a blueprint.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.4
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• pp.781-787
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• 2007

Network Mobility (NEMO) basic support protocol doesn't execute the process of route optimization and has not presented the particular security mechanism in other blocks except hi-directional tunnel between Mobile Router (MR) and its Home Agent (HA). Therefore in this paper we process secure route optimization courses through authenticated binding update protocol between MR and its Correspondent Node (CN) and the protocol of the competency of mandate between MR and its Mobile Network Node (MNN); its block also uses an bi-directional tunnel as the block between MR and its HA. The address of each node are generated by the way of Cryptographically Generated Address (CGA) for proving the ownership of address. Finally we analyze the robustness of proposed protocol using security requirements of MIPv6 and existing attacks and the efficiency of this protocol using the connectivity recovery and end-to-end packet transmission delay time.