Pyeongtaek, South Korea
Pyeongtaek, South Korea

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Shakhov V.,Russian Academy of Sciences | Nam S.,Kookje College | Choo H.,Sungkyunkwan University
Proceedings of the 7th International Conference on Ubiquitous Information Management and Communication, ICUIMC 2013 | Year: 2013

One of the most critical damaging effects on most wireless sensor networks is a flooding attack. Flooding threat occurs not only from spoofed packets generators launched by intruders but also from the inherent behavior of the network protocols. Flooding harm can be categorized into two types as follows. First, a sensor cannot provide required services when it receives a lot of packets. An essential part of packets are rejected and packets delay becomes inadmissible. And second, if a sensor transmits many packets then the sensor battery is quickly exhausted. Energy harvesting technologies offers the potential of reducing the second vulnerability. This paper explores the operation of wireless sensor networks with energy harvesting capability taking into account both flooding negative effects above. We consider the feasibility and threats of the attacks and their impacts. We then propose a theoretical analysis of the flooding attacks. The corresponding mathematical model is offered. Counteracting methods against such intrusions is discussed. Copyright © 2013 ACM.

Choi M.,Pohang University of Science and Technology | Choi J.,Pohang University of Science and Technology | Nam S.Y.,Kookje College | Chung W.K.,Pohang University of Science and Technology
Proceedings - IEEE International Conference on Robotics and Automation | Year: 2012

The scan matching is widely used for localization and mapping of mobile robots. In this paper, a direction of data point in the scan is approximated and this is incorporated into the scan matching algorithm to improve the performance. The direction of data point is the normal direction of the least squares fitted line based on neighbors of the data point. Owing to this incorporation, the performance of the scan matching can be improved. The number of iterations decreases, and the tolerance against a large relative-rotation between scans increases. Using real sensor data of a laser range finder, experimental results verify the performance of the proposed algorithm, the direction augmented probabilistic scan matching. © 2012 IEEE.

Joung W.-I.,Kookje College | Cho T.-S.,Chungwoon University
Communications in Computer and Information Science | Year: 2012

This essay bases on the semiological analysis on the lyrics of the 70's folk songs. For the analysis, it is essential to understand the contemporary social phenomenon. At the time, everything, from hair to ladies' skirts, was controlled by the military regime. It is not difficult to deduce that culture was another victim of it. I study about the youth's mind in the contemporary society and how the lyrics of the songs represented their mind. © 2012 Springer-Verlag Berlin Heidelberg.

Lee S.-H.,Semyung University | Lee K.-S.,Semyung University | Yoo J.-H.,Semyung University | Jeong Y.-H.,Korea University | Yoon H.-S.,Kookje College
Transactions on Electrical and Electronic Materials | Year: 2011

In this study, (K0.5Na 0.5)(Nb0.97Sb0.03)O3+0.9mol% K5.4Cu1.3Ta10O29+x mol%K4CuNb8O23 (x = 0, 0.2,0.6,0.8) ceramics were prepared by a conventional mixed oxide method. Their microstructure and electric properties were investigated. The secondary phase was made by virtue ofK4CuNb8O23 (KCN) addition in the (K0.5Na0.5)(Nb0.97Sb0.03)O3 system ceramics. However, the sinterability of the ceramics increased with increasing K4CuNb8O23 content. At the 0.6 mol% K4CuNb8O23 added composition ceramics sintered at 1,060° C kp and d33 showed the optimum values of 0.39 and 145 pC/N, respectively, suitable for piezoelectric actuator application. © 2011 KIEEME.

Shakhov V.,Russian Academy of Sciences | Nam S.,Kookje College | Shin S.J.,Hansei University | Choo H.,Sungkyunkwan University
Proceedings of the 6th International Conference on Ubiquitous Information Management and Communication, ICUIMC'12 | Year: 2012

In this paper, a novel type of potential attacks on wireless networks is considered. The means of intruder is unauthorized high power of a signal transmitted by wireless devices. A destructive effect of the attack depends on the type of network. In case of cellular networks an attacked mobile phone generates excessive electromagnetic emissions for a long period of time. Thus, objects of attack are mobile phone owners. In case of wireless sensor networks an illegal increase in the transmitting power exhausts a sensor battery. Thus, the lifetime of a sensor is depredated. Counteracting against such intrusions is discussed. © 2012 ACM.

Do N.T.,Hongik University | Dung L.T.,Hongik University | An B.,Hongik University | Nam S.-Y.,Kookje College
International Conference on Electronics, Information, and Communications, ICEIC 2016 | Year: 2016

In this paper, we study the connectivity of a hybrid cognitive radio ad hoc network (H-CRAHN) in which each secondary user can be able to use either overlay cognitive radio or underlay cognitive radio paradigms to access a licensed spectrum. Specifically, we carry out a simulation-based analysis to investigate the connectedness between two arbitrary nodes in the H-CRAHN. Considering such a hybrid network, we propose an algorithm to calculate the path probability which measures the connectivity of the network. We then exam what network parameters that impact on the connectivity of the H-CRAHN. The simulation results show that by using the hybrid underlay/overlay transmission mode at the SUs, the path probability increases compared to the use of only underlay mode or overlay mode. In addition, active rate of primary user, node density, and transmit power play key roles in the study of the network connectivity. © 2016 IEEE.

Shim K.,Hongik University | Do N.T.,Hongik University | An B.,Hongik University | Nam S.-Y.,Kookje College
International Conference on Electronics, Information, and Communications, ICEIC 2016 | Year: 2016

In this paper, we consider a multi-hop decode-and-forward (DF) relaying transmission in underlay cognitive radio networks. Considering the presence of an eavesdropper that overhears the transmission, we address secure communications of multi-hop wireless communications in terms of physical layer security. In addition, we take in to account the effect of imperfect channel state information (CSI) which is of importance issue in underlay cognitive radio. We analyze the secrecy outage performance of the system over Rayleigh fading channels. In particular, we derive the closed-form expression of the system secrecy outage probability. The analysis results are validated by the Monte-Carlo simulation results. The numerical results show that the imperfect CSI issue does not effect on the security issue of the transmission in underlay cognitive radio networks. On the other hand, the number of hops plays a key role in the physical layer security. © 2016 IEEE.

Park K.,Korea University | Lee T.,Korea University | Jung S.,Korea University | Lim H.,Korea University | Nam S.,Kookje College
2010 2nd International Conference on Information Technology Convergence and Services, ITCS 2010 | Year: 2010

Web search users complain of inaccurate results of the current search engines. Most of inaccurate results are from failing to understand user's search goal. This paper proposes a method to mine user's intentions and to build an intention map representing their information needs. It selects intention features from search logs obtained from previous search sessions on a given query and extracts user's intentions by using clustering and labeling algorithms. The mined user's intentions on the query are represented in an intention map. For the efficiency analysis of intention maps, we extracted user intentions using 2,600 search log data of a current domestic commercial web search engine. The experimental results using a web search engine with the intention maps show statistically significant improvements in user satisfaction scores. © 2010 IEEE.

Lee J.-S.,Pohang University of Science and Technology | Nam S.Y.,Kookje College | Chung W.K.,Pohang University of Science and Technology
Advanced Robotics | Year: 2011

We propose a robust simultaneous localization and mapping (SLAM) with a Rao-Blackwellized particle filter (RBPF) algorithm for mobile robots using sonar sensors in non-static environments. The algorithm consists of three parts: sampling from multiple ancestor sets, estimating intermediate paths for map updates and eliminating spurious landmarks using negative information from sonar sensors. The proposed sampling method, in which particles are sampled from multiple ancestor sets, increases the robustness of the estimation of the robot's pose, even if environmental changes corrupt observations. This step increases the probability of some particles being sampled from correct ancestor sets that are updated by observations reflected from stationary objects. When particles are sampled from several time steps earlier, however, observations at intermediate time steps cannot be used to update the map because of the lack of information about the intermediate path. To update the map with all sensor information, the intermediate path is estimated after particles are sampled from ancestor sets. Finally, spurious landmarks still exist on the map representing objects that were eliminated or that were extracted by error in cluttered areas. These are eliminated in the final step using negative information from the sonar sensors. The performance of the proposed SLAM algorithm was verified through simulations and experiments in various non-static environments. © 2011 Koninklijke Brill NV, Leiden.

Choi J.,Pohang University of Science and Technology | Choi M.,Pohang University of Science and Technology | Nam S.Y.,Kookje College | Chung W.K.,Pohang University of Science and Technology
Autonomous Robots | Year: 2011

This paper presents a method of autonomous topological modeling and localization in a home environment using only low-cost sonar sensors. The topological model is extracted from a grid map using cell decomposition and normalized graph cut. The autonomous topological modeling involves the incremental extraction of a subregion without predefining the number of subregions. A method of topological localization based on this topological model is proposed wherein a current local grid map is compared with the original grid map. The localization is accomplished by obtaining a node probability from a relative motion model and rotational invariant grid-map matching. The proposed method extracts a well-structured topological model of the environment, and the localization provides reliable node probability even when presented with sparse and uncertain sonar data. Experimental results demonstrate the performance of the proposed topological modeling and localization in a real home environment. © Springer Science+Business Media, LLC 2011.

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