• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.5
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• pp.37-45
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• 2004

As Internet technologies are mature, many new applications that are different characteristics are emerging. Recently we see wide use of P2P(Peer to Peer) applications of which traffic shows different statistical characteristics compared with traditional application such as web(HTTP) and FTP(File Transfer Protocol). In this paper, we measured subscriber network of KT(Korea Telecom) to analyze P2P traffic characteristics. We show flow characteristics of measured traffic. We also estimate Hurst parameter of P2P traffic and compare self-similarity with web traffic. Analysis results indicate that P2P traffic is much bustier than web traffic and makes both upstream traffic and downstream traffic be symmetric. To predict parameters related QoS such as packet loss and delays we model P2P traffic using two self-similar traffic models and predict both loss probability and mm delay then compare their accuracies. With simulation we show that the self-similar traffic models we derive predict the performance of P2P traffic accurately and thus when we design a network or evaluate its performance, we can use the P2P traffic model as reference input traffic.

• Journal of the Korean Society for information Management
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• v.32 no.2
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• pp.105-129
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• 2015

The purpose of this study was to explore the effects of librarian's empowerment and organizational commitment on organizational effectiveness in libraries. The subjects of this study were 148 librarians of 10 libraries in Jeollabuk-do in accordance to purposeful sampling of nonprobability sampling. The statistics program that was used to achieve the purpose was SPSS pc+ 20.0. The statistics methods were used one-way ANOVA, Pearson's correlation analysis, and multiple regression test. The following conclusion were drawn from the research procedures and data analysis. First, the librarian's empowerment level and organizational effectiveness make a difference by age level. But the librarian's organizational commitment make no difference by age level. Second, the librarian's empowerment level make a difference by marital status. But the librarian's organizational commitment and effectiveness make no difference by marital status. Third, the librarian's empowerment level make a difference by career in present librarian. But the librarian's organizational commitment and effectiveness make no difference by career in present librarian. Fourth, Very a high correlation is influence factor and all of the empowerment, competence factor, and all of the empowerment. Fifth, the organizational effectiveness is affected 9.3% by librarian's empowerment, 5.6% by librarian's organizational commitment.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.5
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• pp.565-570
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• 2015

Spread spectrum communications have increased interest due to their immunity to channel fading and low probability of intercept. One of the limitations of the traditional digital spread spectrum systems is the need for spreading code synchronization. Chaotic communication is the analogue alternative of digital spread spectrum systems beside some extra features like simple transceiver structures. In this paper, This paper was used instead of the digital modulation and demodulation carriers for use in the chaotic signal in a digital communication system among the chaotic modulation schemes, the Differential Chaos Shift Keying(DCSK) is the most efficient one because its demodulator detects the data without the need to chaotic signal phase recovery. Also Implementation of Differential Chaos Shift Keying Communication System Using Matlab/Simulink and the receiver con decode the binary information sent by the transmitter, performance curves of DCSK are given in terms of bit-error probability versus signal to noise ratio with spreading factor as a parameter and we compare it to BPSK modulation.

• The Korean Journal of Applied Statistics
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• v.6 no.1
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• pp.125-143
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• 1993

The primary objective of the paper is to review the development of approximations of the null distribution of a scan statistic and to show how these approximations were improved. Let $X_1, \cdots, X_N$ be a sequence of independent uniform random variables on an interval (0, t]. A can statistic is defined to be the maximum number of observations in a subinterval of length t $\leq$ T, when we continuously (or discretely) move the subinterval from 0 to T. A scan statistic is used to test whether certain events occur in a cluster aganist a null hypothesis of the uniformity. It is difficult to calculate the exact null distribution of a scan statistic. Several authors have suggested approximations of the null distribution of a scan statistic since Naus(1966). We conceive that a scan statistic can be used for detecting a "hot region" is defined to be a region at which the frequencies of mutations are relatively high. A "hot region" may be regarded as a generalized version of a hot spot. We leave it for a further study the concrete formulation of deteciton a "hot region" in a mutational spectrum.uot; in a mutational spectrum.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.1
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• pp.1-10
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• 1989

The stress history of a bridge is different depending on the characteristic of traffic flow. Because the flow is varied with vehicle type, weight and headway time etc., statistical analysis in bridges is necessary to estimate the history by traffic flow. By applying the statistical analyses in fracture mechanics, the remaining service life of the structure can be estimated. In this paper, 1)the statistical analysis of vehicle type, weight and headway time etc. to analysis randomness of traffic flow, 2)measuring and analysis of stress history of a real bridge, 3)reappearance of stress history by Monte-Carlo Simulation using constitution ratio of vehicle type, weight and headway time as probabilitic variable, 4)comparision of the calculated and modelled stress history, 5)calculation of reduction factor, 6)comparision of frequency of stress range depending on span length etc. were performed. From the results, the basic modelled stress history which is necessary for the method of estimation of the remaining service life of the structure could be suggested.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.36C no.11
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• pp.75-83
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• 1999

We propose a PfSGA(parameter-free species genetic algorithm) to learn the topological structure of MLP classifiers being adequate to given applications. The PfSGA is a combinational method of SGA(species genetic algorithm) and PfGA(parameter-free genetic algorithm). In SGA, we divide the total search space into several subspaces(species) according to the number of hidden units, and reduce the unnecessary search by eliminating the low promising species from the evolutionary process. However the performances of SGA classifiers are readily affected by the values of parameters such as mutation ratio and crossover ratio. In this paper, therefore, we combine SGA with PfGA, for which it is not necessary to determine the learning parameters. Experimental results on benchmark data and sign language words show that PfSGA can reduce the learning time of SGA and is not affected by the selection parameter values on structural learning. The results also show that PfSGA is more efficient than the exisiting methods in the aspect of misclassification ratio, learning rate, and complexity of MLP structure.

• Journal of Korea Water Resources Association
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• v.53 no.10
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• pp.917-928
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• 2020

The purpose of this study is to find the appropriate probability distribution representing the size distribution of suspended cohesive sediment. Based on goodness-of-fit test for a significance level of 5% using the Kolmogorov-Smirnov test, it is found that the floc size distributions measured in laboratory experiment and field study show different results. In the case of sample data collected from field experiments, the Gamma distribution is the best fitting form. In the case of laboratory experiment results, the sample data shows the positively-skewed distribution and the GEV distribution is the best fitted. The lognormal distribution, which is generally assumed to be a floc size distribution, is not suitable for both field and laboratory results. By using 3-parameter lognormal distribution, it is shown that similar size distribution with floc size distribution can be simulated.

• Journal of KIISE:Information Networking
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• v.31 no.2
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• pp.188-195
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• 2004

We have analyzed the performance of TCP in the CDMA mobile communications systems with the adaptive modulation and coding(AMC). The wireless channel using AMC is characterized with not high error rate but highly varying bandwidth. Due to time-varying bandwidth, timeout events of TCP occurs more frequently, which leads to the throughput degradation. The analysis model is composed of the two parts. In the first part, we divide TCP packet stream into ‘packet groups’and derive the probability distribution of the wireless transmission time of each Packet group that reflects the time varying characteristics of AMC. In the second part, we formulate embedded Markov chain by making use of the results of the first part to model TCP timer mechanism and wireless transmission. Since our system model is characterized by the forward link high speed data transmission using AMC, the results reported in this paper can be used as a guideline for the design and operation of HSDPA, 1xEV-DO, and 1xEV-DV.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.8
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• pp.1613-1621
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• 2015

This paper analyzes the rate adaptation scheme and suggests applicable strategy of the MCS(Modulation and Coding Scheme) for improving DCF throughput in the IEEE 802.11ad and 802.11ad wireless LAN. IEEE 802.11ac and 802.11ad wireless LAN provide MCS technique that dynamically adjusts modulation level and code rate to the time-varying channel conditions in order to obtain considerably high data rates. But these standards did not provide rate adaptation algorithm, so this paper surveyes rate adaptation algorithm and suggests MCS scheme applied to IEEE 802.11ac and 802.11ad wireless LAN. Specially A MAC(Medium Access Control) layer throughput is evaluated over error-prone channel in the IEEE 802.11ac-based wireless LAN. In this evaluation, DCF (Distributed Coordination Function) protocol and A-MPDU (MAC Protocol Data Unit Aggregation) scheme are used. Using theoretical analysis method, the MAC saturation throughput is evaluated with the PER (Packet Error Rate) on the condition that the number of station, transmission probability, the number of parallel beams and the number of frames in each A-MPDU are variables.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.1A
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• pp.142-155
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• 2000

In this paper, we propose an efficient policing mechanism for Markov model-based traffic descriptors of VBR MPEG video traffic. A VBR video sequence is described by a set of traffic descriptors using a scene-basedMarkov model to the network for the effective resource allocation and accurate QoS prediction. The networkmonitors the input traffic from the source using a proposed new policing method. for policing the steady statetransition probability of scene states, we define two representative monitoring parameters (mean holding andrecurrence time) for each state. For frame level cell rate policing of each scene state, accumulated average cellrates for the frame types are compared with the model parameters. We propose an exponential bounding functionto accommodate dynanic behaviors during the transient period. Our simulation results show that the proposedpolicing mechanism for Markovian traffic descriptors monitors the sophisticated traffic such as MPEG videoeffectively and well protects network resources from the nalicious or misbehaved traffic.