• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.6
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• pp.119-130
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• 2010

The universal model for the parameter estimation of the Storage Function Model(SFM) was developed through the applications of the distributed model for various hypothetical watersheds and runoff conditions. The existing parameter estimation equations are based on observations and these equations which are derived from the restricted conditions are not sensitive to the variation of physical characteristics of a watershed. This study developed the universal model for the parameter estimation through the runoff simulations of 35,000 times. As the simulation results, we have known that the lag time is related to the longest stream channel characteristics and the storage coefficient is related to the watershed characteristics.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.5
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• pp.1002-1011
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• 2005

In this paper. we design and implement a bi-directional broadcasting system, so called return channel server, to allow users to participate in a broadcasting program by using a hi-directional interaction channel. To provide user participation in a program and reflect the user's opinions or responses in real time, the return channel server can be viewed as consisting of four major functional modules: a control module, network interface module, DBMS module, and real-time content authoring module. To construct a return channel server that has a service independent architecture, we designed a return channel server to include the hierarchical structure. The presented return channel server consists of two parts: an RCSAE(return channel server application environment) and RCSA(return channel server application). An RCSA is composed of an execution code and a parameter for executing the execution code. RCSA defines the procedures for providing a specific broadcasting program using the return channel server. On the other hand, an RCSAE provides the environment for the execution of RCSAS. By adopting RCSAE and RCSA, we construct the return channel server that has a service-independent architecture which are shown by the test.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.4C
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• pp.411-417
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• 2007

The rate control is an essential component in video coding to provide better quality under given coding constraints, such as channel capacity, frame rates, etc. In general, source data cannot be described as a single distribution in a video coding, hence it can cause an exhaustive approximation problem. It drops a coding efficiency under weak channel environments, such as mobile communications. In this paper, we design a new quantization parameter decision model that is based on a rate-distortion function of generalized Gaussian distribution. In order to adaptively express various source data distribution, we decide a shape parameter by observing a ratio of samples, which have a small value. For experiment, the proposed algorithm is implemented into H.264/AVC video codec, and its performance is compared with that of MPEG-2 TM5, H.263 TMN8 rate control algorithm. As shown in simulation results, the proposed algorithm provides an improved quality rather than previous algorithms and generates the number of bits closed to the target bits.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.4
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• pp.7-12
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• 2019

Ambient backscatter communication is limited to channel estimation technique through a pilot signal, which is a channel estimation method in current RF communication, due to transmission power efficiency. In a limited transmission power environment, the research of traditional ambient backscatter communication has been studied assuming that it is an ideal channel without signal distortions due to channel conditions. In this paper, we propose an expectation-maximization(EM) algorithm, one of the blind channel estimation techniques, as a channel estimation method in ambient backscatter communication system which is the state of channel following normal distribution. In the proposed system model, the simulations confirm that channel estimate through EM algorithm is approaching the lower bound of the mean square error compared with the Bayesian Cramer-Rao Boundary(BCRB) to check performance. It shows that the channel parameter can be estimated in the ambient backscatter communication system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.7
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• pp.706-712
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• 2004

This paper presents the design technique of output multiplexer(OMUX) for the Ka-band satellite transponder. Output multiplexer consists of low-pass filter(LPF), channel filter and manifold. Channel filters adopt dual-mode technique in design for mass and volume reduction and frequency response of channel filters is 4-pole elliptic response for high frequency selectivity. w-pass filters are designed to be of 13th order corrugated type for high rejection characteristic over reception band of satellite transponder. After initial design of channel filters and manifold, we optimized only a few design parameters for fast and easy optimization instead of optimizing all the design parameter. Measured results of a realized output umltiplexer for Ka-band satellite transponder show good agreement with the computed ones.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.5A
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• pp.409-416
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• 2007

In cellular orthogonal frequency division multiplexing (OFDM) networks, co-channel interference (CCI) leads to severe degradation in the BER performance. To solve this problem, maximum-likelihood estimation (MLE) CCI cancellation scheme has been proposed in the literature. MLE CCI cancellation scheme generates weighted replicas of the transmitted signals where weights represent the estimated channel transfer functions. The replica with the smallest Euclidean distance from the received signal is selected and data are detected. When the received power of the desired and interference signals are nearly the same, the BER performance is degraded. In this paper, we propose a closed-loop power control (PC) scheme capable of detecting the equal received power situation at the mobile station (MS) receiver by using the newly introduced parameter power ratio (PR). When this situation is detected, the MS sends a feedback to the desired base station (BS) which boosts the transmission power in the next frame. At cell edge where signal to interferer ratio (SIR) is considered to have average value between -5 dB and 10 dB, computer simulations show that the proposed CCI cancellation scheme has a gain of 7 dB at 28 Km/h.

• International Journal of Fluid Machinery and Systems
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• v.5 no.3
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• pp.100-108
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• 2012

Design parameters for suction channels of process centrifugal compressors were investigated, and an optimization method to enhance stage efficiency by using the new design parameters was proposed. From results of computational fluid dynamics, the passage sectional area ratios $A_c/A_e$, $A_e/A_s$ and $A_c/A_s$ were found to be the dominant parameters for the pressure loss and circumferential flow distortion, where $A_c$, $A_e$ and $A_s$ are passage sectional areas for the casing upstream side, casing entrance and impeller eye, respectively. The Base suction channel was optimized using the new design parameters, and the Base and Optimized types were tested. Test results showed that the Optimized suction channel achieved 3.8% higher stage efficiency than the Base suction channel while maintaining the same operating range.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.2 no.1
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• pp.43-48
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• 2002

This paper discusses the application of fuzzy-ARTMAP neural network to compensate the nonlinearity of satellite communication channel. The fuzzy-ARTMAP is the class of ART(adaptive resonance theory) architectures designed fur supervised loaming. It has capabilities not fecund in other neural network approaches, that includes a small number of parameters, no requirements fur the choice of initial weights, automatic increase of hidden units, and capability of adding new data without retraining previously trained data. By a match tracking process with vigilance parameter, fuzzy-ARTMAP neural network achieves a minimax teaming rule that minimizes predictive error and maximizes generalization. Thus, the system automatically leans a minimal number of recognition categories, or hidden units, to meet accuracy criteria. As a input-converting process for implementing fuzzy-ARTMAP equalizer, the sigmoid function is chosen to convert actual channel output to the proper input values of fuzzy-ARTMAP. Simulation studies are performed over satellite nonlinear channels. QPSK signals with Gaussian noise are generated at random from Volterra model. The performance of proposed fuzzy-ARTMAP equalizer is compared with MLP equalizer.

• Journal of Digital Contents Society
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• v.5 no.2
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• pp.121-127
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• 2004

In this paper, we have analyzed the error performance of OFDM (Orthogonal Frequency Division Multiplexing 16 QAM (Quadrature Amplitude Modulation) Signal in a multipath fading environment modeled as frequency selective Rician fading. We have used a three-path model as frequency selective Rician fading used Rician parameter K. A BCH channel coding is used in order to improve the performance. From the result of this analysis, we have known the improvement of the error performance improvement and the error correcting capability by the BCH channel coding. From the results, the error performance, about $10^{-6},$ required in wireless multimedia communications can not be achieved by using only the BCH channel coding technique so that it should be adopted a new technique together.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.5
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• pp.1075-1082
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• 1997

In this paper, we propose a channel assignment scheme for reducing call blocking rate in a base station(BS) of DS-CDMA cellular systems. The proposed scheme can e applied to the case where the capacity of reverse radio link is enough, but not are the available traffic channels performing the digital modulation and demodulation functions between a mobile station and the base station. The proposed scheme takes advantage of the feature of soft handoff in which a mobile station keeps its communication link even if one of the two communication links is released. The scheme estimates the mean and variance of the received power level measured at the base station before assigning a traffic channel for a new call request. The BS makes decision based on the estimated balues whether the new call request will be accepted or not. If it is decided that the capacity of reverse radio link is enough, but all traffic channels are not available, then the BS increases the soft handoff parameter T_DROP to release the traffic channels of mobile stations loactedin soft handoff area. The BS assigns the released traffic channel to anew call or a handoff call. The performance of the proposed channel assignment scheme is evaluated by computer simulation. The results show that the call blocking rate for new calls and handoff calls is reduced.