• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.12
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• pp.1102-1112
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• 2012

We propose a cell selection and resource allocation scheme that assigns users to nearby accessible cells in heterogeneous wireless networks consisting of macrocell, femtocells, and Wi-Fi access points, under overload situation. Given the current power level of all accessible cells nearby users, the proposed scheme finds all possible cell assignment mappings of which user should connect to which cell to maximize the number of users that the network can accommodate at the same time. We formulate the cell selection problem with heterogeneous cells into an optimization problem of binary integer programming, and compute the optimal solution. We evaluate the proposed algorithm in terms of network access failure compared to a local ad-hoc based cell selection scheme used in practical systems using network level simulations. We demonstrate that our cell selection algorithm dramatically reduces network access failure in overload situation by fully leveraging network resources evenly across heterogeneous networks. We also validate the practical feasibility in terms of computational complexity of our binary integer program by measuring the computation time with respect to the number of users.

• Communications of Mathematical Education
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• v.28 no.4
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• pp.457-474
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• 2014

Recently, with the development of technology, intuitive understanding of abstract mathematical concepts through visualizations is growing in popularity within college mathematics. In this study, we introduce free visualization tools developed for better understanding of topics which students learn in Calculus. We visualize important concepts of Calculus as much as we can according to the order of most Calculus textbooks. In this process, we utilized a well-known, free mathematical software called GeoGebra. Finally, we discuss our experience with visualizations in Calculus using GeoGebra in our class and discuss how it can be effectively adopted to other university math classes and high school math education.

• Journal of Elementary Mathematics Education in Korea
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• v.18 no.1
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• pp.37-62
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• 2014

In this thesis, we inquire into teaching method of decimal fraction concept in elementary mathematics education based on measurement activity. For this purpose, our research tasks are as follows: First, we design a experimental learning-teaching plan of 'decimal fraction' unit in 4th grade textbook and verify its effect. Second, after teaching experiment using experimental learning-teaching plan, we analyze the student's status of understanding about decimal fraction concept. As stated above, we have performed teaching experiment which is ruled by new lesson design and analysed the effects of teaching experiment. Through this study, we obtained the following results. First, introduction of decimal fraction based on measurement activity promotes student's understanding of measuring number and decimal notation. Second, operator concept of decimal fraction is widely used in daily life. Its usage is suitable for elementary mathematics education within the decimal notation system. Third, a teaching method of times concepts using place value expansion of decimal fraction is more meaningful and has less possibility of misunderstanding than mechanical shift of decimal point. Fourth, teaching decimal fraction through the decimal expansion helps students with understanding of digit 0 contained in decimal fraction, comparing of size and place value. Fifth, students have difficulties in understanding conversion process of decimal fraction into decimal notation system using measurement activity. It can be done easily when fraction is used. However, that is breach to curriculum. It is necessary to succeed research for this.

• Journal of Information Management
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• v.34 no.2
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• pp.55-66
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• 2003

The Web is rich with various sources of information. It contains the contents of documents, multimedia data, shopping materials and so on. Due to the massive and heterogeneous web document collections, users want to find various types of target pages. We can classify user queries as three categories according to users'intent, content search, the site search, and the service search. In this paper, we present that different strategies are needed to meet the need of a user. Also we show the properties of content information, link information and URL information according to the class of a user query. In the content search, content information showed the good result. However, we lost the performance by combining link information and URL information. In the site search, we could increase the performance by combining link information and URL information.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.7
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• pp.1785-1796
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• 1998

This paper is concerned with the relationships between optimal number of wavelengths and tuning time in time division multiplexing(TDM) scheduling on wavelength division multiplexing(WDM) optical passive star networks. We assume that the traffic is nonuniform and each node has a tunable transmitter and a fixed receiver. Each node transmits spckets to all other nodes. Most of the earlier protocols on TDM based scheduling for WDM star networks [7, 8, etc.] use whold given wavelength chnnels. But in this paper, we investigate the optimal number of wavelengths that yidels minimum frame length when tuning time exists. It appears within the availble number of wavelengths that yields minimum frame length when tuning time exists. It appears within the available number of wavelengths. We analyze the relationships between optimal number of wavelengths and tuning time by experiments. We analyze the reationships between optimal number of wavelengths and tuning time by experiments. We also discuss on the possibility of reduction of frame length by increasing the number of nodes trans-mitters and receivers.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.1
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• pp.31-38
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• 2017

In this paper, we have designed MIMO system using F-OFDM modulation. And then, we have evaluated and analyzed synchronization performance of the system. In this paper we have considered Schmidl's method, Minn's method, and Park's method. As simulation results, Schmidl's method has wide plateau of timing metric and Park's method has impulse-shape timing metric. Also, we can confirm that timing metric characteristic of synchronization estimator can be degraded by adjusting filter length of F-OFDM system. Especially, we can confirm that timing metric of synchronization estimator is shifted according to filter length of MIMO system using F-OFDM modulation and this timing metric movement can be compensated by using designed filter length.

• Journal of the Korea Society of Computer and Information
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• v.17 no.4
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• pp.67-74
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• 2012

In this paper, we propose an efficient dynamic background modelling method by using eigenbackground to extract moving objects from video stream. Even if a background model has been created, the model has to be updated to adapt to change due to several reasons such as weather or lighting. In this paper, we update a background model based on R-SVD method. At this time we define a change ratio of images and update the model dynamically according this value. Also eigenbackground need to be modelled by using sufficient training images for accurate models but we reorganize input images to reduce the number of images for training models. Through simulation, we show that the proposed method improves the performance against traditional eigenbackground method without background updating and a previous method.

• Journal of Korea Technology Innovation Society
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• v.11 no.3
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• pp.335-351
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• 2008

The paper constructs the economic theory of sleeping patents in the knowledge-based economy. Starting with the definition of sleeping patents, we suggest the types of sleeping patents, intended and unintended ones. While intended sleeping patents are divided into 'for-defending technological position' and 'for-describing past technology', unintended sleeping patents include frictional, intrinsic, market-deficient, and institutional ones. We also introduce the concept of the natural rate of sleeping patent and measure the social loss due to sleeping patents. The study can contribute to solving policy problems for utilizing registered patents. For example, if we measure the natural rate of sleeping patent in Korea, we can estimate 'tolerable rate of sleeping patent' and control the extend of policy intervention for patents utilization. Since we invest the theory of sleeping patents firstly, the suggested concepts should be elaborated through further discussion in depth.

• Journal of Digital Convergence
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• v.15 no.2
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• pp.335-345
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• 2017

It is necessary for an instructor to understand the student's team building behavior for an effective guidance of team activities. In this study, we developed an agent-based computational model for simulating the student's self-controlled behavior. We validated the model by comparing the actual behavior. Through the simulation, we found that the time to stabilization of team formation and the ratio of the students having no team are decreasing as the population of the student increases. However, we also found that over a certain amount of population, the time and the ratio do not show much progress in the difference. The simulation also shows that the more heterogeneity between the students the higher chance of delaying the team formation and increasing the ratio. We expect to use the model as a tool for guiding and supporting students' team activities.

• Journal of Satellite, Information and Communications
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• v.9 no.4
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• pp.97-103
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• 2014

In order to verify normal operation of satellite OBC(On Board Computer), it is essential that processor monitoring and debugging. So we are using the GRMON of Aeroflex Gaisler. It provides a lot of features for debugging of LEON processor but we can't use that features on the NGSCB(Next Generation Spacecraft Computer Board) except a few things. So the cost-effectiveness is very low. And for hardware fault injection, we are using a method of modify satellite flight software, because we can't modify GRMON. This method can not guarantee normal operation of the satellite flight software. So in this paper we were developed the processor monitoring and fault injection tool for NGSCB.