• Proceedings of the Korean Operations and Management Science Society Conference
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• 2001.10a
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• pp.342-345
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• 2001

Telecommunication services are distinctive in that their adoptions are influenced by network effect resulting in 'the late take-off Phenomenon' and the 'critical mass' problem. In this paper we examined, so called, 'the late take-off phenomenon' in the diffusion process of telecommunication services. We compared the parameters of the diffusion process of consumer durables with those of fax services in the US and Korea. By analyzing the parameters of a new diffusion model based on the threshold model proposed by Markus, We found that 'the late take-off phenomenon' resulted from the low heterogeneity of the threshold distribution for the potential adopters.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.2164-2168
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• 2003

Real time control system such as in factory automation fields, defense field, aerospace, railway industries, financial trading and so forth, includes multiple computers on multiple nodes, and share data to process various actions and functions. This is similar to multitasking in a multiprocessor computer system. The task processing efficiency of such system is proportionally increased by process speed of each process computer. And also it is greatly influenced by communication latencies of each node. To provide proper operation of such real time system, a network that can guarantee deterministic exchange of certain amount of data within a limited time is required. Such network is called as a real time network. As for modern distributed control system, the timeliness of data exchange gives important factor for the dynamics of entire control system. In a real time network system, exchanged data are determined by off-line design process to provide the timeliness of data. In other word, designer of network makes up a network data table that describes the specification of data exchanged between control equipments. And by this off-line design result, the network data are exchanged by predetermined schedule. First, this paper explains international standard real time network TCN (Train Communication Network) applied to the KHST (Korean High Speed Train) project. And then it explains the computer program developed for design tool of network data table of TCN.

• Journal of Communications and Networks
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• v.18 no.2
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• pp.227-237
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• 2016

Data collection is a key function for wireless sensor networks. There has been numerous data collection scheduling algorithms, but they fail to consider the deep and complex relationship among network lifetime, sink aggregated information and sample cycle for wireless sensor networks. This paper gives the upper bound on the sample period under the given network topology. An optimal schedule algorithm focusing on aggregated information named OSFAI is proposed. In the schedule algorithm, the nodes in hotspots would hold on transmission and accumulate their data before sending them to sink at once. This could realize the dual goals of improving the network lifetime and increasing the amount of information aggregated to sink. We formulate the optimization problem as to achieve trade-off among sample cycle, sink aggregated information and network lifetime by controlling the sample cycle. The results of simulation on the random generated wireless sensor networks show that when choosing the optimized sample cycle, the sink aggregated information quantity can be increased by 30.5%, and the network lifetime can be increased by 27.78%.

• Proceedings of the Korea Society of Design Studies Conference
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• 2002.11b
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• pp.118-119
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• 2002

• Journal of the Korean Institute of Intelligent Systems
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• v.14 no.1
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• pp.118-124
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• 2004

In this paper, we present a indirect adaptive control method using a wavelet neural network (WNN) for the control of chaotic nonlinear systems without precise mathematical models. The proposed indirect adaptive control method includes the off-line identification and on-line control procedure for chaotic nonlinear systems. In the off-line identification procedure, the WNN based identification model identifies the chaotic nonlinear system by using the serial-parallel identification structure and is trained by the gradient-descent method. And, in the on-line control procedure, a WNN controller is designed by using the off-line identification model and is trained by the error back-propagation algorithm. Finally, the effectiveness and feasibility of the proposed control method is demonstrated with applications to the chaotic nonlinear systems.

• Journal of Communications and Networks
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• v.16 no.1
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• pp.36-44
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• 2014

Exploiting the energy-delay tradeoff for energy saving is critical for developing green wireless communication systems. In this paper, we investigate the delay-constrained energy-efficient packet transmission. We aim to minimize the energy consumption of multiple randomly arrived packets in an additive white Gaussian noise channel subject to individual packet delay constraints, by taking into account the practical on-off circuit power consumption at the transmitter. First, we consider the offline case, by assuming that the full packet arrival information is known a priori at the transmitter, and formulate the energy minimization problem as a non-convex optimization problem. By exploiting the specific problem structure, we propose an efficient scheduling algorithm to obtain the globally optimal solution. It is shown that the optimal solution consists of two types of scheduling intervals, namely "selected-off" and "always-on" intervals, which correspond to bits-per-joule energy efficiency maximization and "lazy scheduling" rate allocation, respectively. Next, we consider the practical online case where only causal packet arrival information is available. Inspired by the optimal offline solution, we propose a new online scheme. It is shown by simulations that the proposed online scheme has a comparable performance with the optimal offline one and outperforms the design without considering on-off circuit power as well as the other heuristically designed online schemes.

• International Journal of Computer Science & Network Security
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• v.24 no.7
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• pp.101-107
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• 2024

Cloud computing is a widely used technology that has changed the way people and organizations store and access information. This technology is quite versatile, which is why extensive amounts of data can be stored in the cloud. Furthermore, businesses can access various services over the cloud without having to install applications. However, the cloud computing services are provided over a public domain, which means that both trusted and non-trusted users can access the services. Though there are several advantages of cloud computing services, especially to business owners, various challenges are also posed in terms of the privacy and security of information and online services. A kind of threat that is widely faced in the cloud environment is the on/off attack. In this kind of attack, a few entities exhibit proper behavior for a given time period to develop a highly a positive reputation and gather trust, after which they exhibit deception. A viable solution is provided by the given trust model for preventing the attacks. This method works by providing effective security to the cloud services by identifying malicious and inappropriate behaviors through the application of trust algorithms that can identify on-off attacks.

• The Journal of the Convergence on Culture Technology
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• v.6 no.1
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• pp.301-312
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• 2020

This study explores the patterns of the self-expression in terms of sharing the diverse pictures according to SNS use focused on the social relationships, and the effects of the diverse online activities on the off-line activity. The study results show that the more SNS use focused on the social relationships, the more sharing the diverse pictures in SNS as a tool of the self-expression. It also shows that the more SNS use focused on the social relationships and the more sharing the pictures with friends, the more active in off-line activity. Both of online and off-line network activities have the statistically significant positive effects on the life satisfaction, which implies that the more active in online and off-line network activities, the higher the life satisfaction.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.5B
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• pp.344-355
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• 2008

In this paper, we are dealing with the problems of performance evaluation of Differentiated Services(DiffServ) networks. For successful performance evaluation, the ability to accurately represent "real" traffic on the network by suitable traffic models is an essential ingredient. Many research results on the nature of real traffic measurements demonstrated LRD(long-range dependence) property for the Internet traffic including Web, TELNET, and P2P traffic. The LRD can be effectively represented by self-similarity. In this paper, we design and implement self-similar traffic generator using the aggregated On/Off source model, based on the analysis of the On-Off source model, FFT-FGN(Fast Fourier Transform-Fractional Gaussian Noise) model, and RMD(Random Midpoint Displacement) model. We confirmed the self-similarity of our generated traffic by checking the packet inter-arrival time of TCPdump data. Further we applied the implemented traffic generator to the performance evaluation of DiffServ networks and observed the effect of performance to the a value of the On/Off model, and performance of EF/BE class traffic by CBQ.

• Proceedings of the IEEK Conference
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• summer
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• pp.317-320
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• 2004

The exponential back-off algorithm doubles the back-off size after each collision without considering network traffic status, which causes degradation of system performance. In this paper, we propose a linear random back-off mechanism which dynamically selects the back-off window size based on the channel status which includes the number of active stations and collisions to significantly increase the protocol capacity. We present an analytical model for the saturated throughput of our linear random back-off algorithm. Simulation results show that performance can be substantially enhanced if binary exponential back-off algorithm is replaced by a linear back- off algorithm.