• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.5A
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• pp.484-492
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• 2006

A multi-code biorthogonal code keying(MBCK) system consists of multiple waveform coding block, and the sum of output codewords is transmitted. Drawback of MBCK is that it requires amplifier with high linearity because its output symbol is multi-level. MBCK with constant amplitude preceding blcok(CA-MBCK) has been proposed, which guarantees sum of orthogonal codes to have constant amplitude. Redundant bits of CA-MBCK for constant amplitude coding are not only used to make constant amplitude signal but also used to improve the bit error rate(BER) performance at receiver. In this paper, we proposed a transmission scheme which combine CA-MBCK with $Q^{2}PSK$ to improve bandwidth efficiency of CA-MBCK. The BER performance of the scheme is same that of CA-MBCK in additive white gaussian noise(AWGN). And we showed that BER performance of the proposed system can be improved using redundant bits of constant amplitude preceding.

• Proceedings of the KIEE Conference
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• 2005.07a
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• pp.277-279
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• 2005

Recently, due to the increase of power conversion devices and nonlinear loads with the development of information, communication and control technologies, the instantaneous minute interruption factors such as voltage & current harmonics, surge occurring frequency, instantaneous voltage variation, voltage unbalance, flicker etc. have greatly threatened the power quality, and the deterioration of electric power facilities and the functional error of controllers are increasing. As such an instantaneous minute interruption appears to be small and local, accurate evaluation with measurement is difficult and total analysis system is required through a wide range of power quality effect analysis such as the simultaneous measurement on various power supply phenomena and the analysis on the interrelation with system loads. Most of conventional power quality diagnosis equipments have beer developed and applied, which were able to measure the stability rate of frequency, the stability rate of voltage, the electricity-failure duration etc, However, they were insufficient to analyze the system present situation, understand the cause of the failure occurred by the problem of power quality and analyze out the phenomena. Accordingly, this study will address the development of the system for a wide range of power quality diagnosis over the present level, the system for supporting the determination such as the analysis on risk factors, failure mode and impact, the system for harmonic evaluation based on international standards(IEC 61000 Series) and the total power quality diagnosis network & system with the extension and openness as a local and national-scale broadband power quality diagnosis system.

• The Korean Journal of Applied Statistics
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• v.19 no.1
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• pp.171-181
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• 2006

The Wald confidence interval has been considered as a standard method for the difference of proportions. However, the erratic behavior of the coverage probability of the Wald confidence interval is recognized in various literatures. Various alternatives have been proposed. Among them, Agresti-Caffo confidence interval has gained the reputation because of its simplicity and fairly good performance in terms of coverage probability. It is known however, that the Agresti-Caffo confidence interval is conservative. In this note, a confidence interval is developed using the weighted Polya posterior which was employed to obtain a confidence interval for the binomial proportion in Lee(2005). The resulting confidence interval is simple and effective in various respects such as the closeness of the average coverage probability to the nominal confidence level, the average expected length and the mean absolute error of the coverage probability. Practically it can be used for the interval estimation of the difference of proportions for any sample sizes and parameter values.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.2151-2155
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• 2008

In case of constructing final closure in sea having big tide variation, the velocity in gap and the seepage velocity under the revet are faster because of inner and outer water level difference of the revet. Thus, the rubbles for final closure lose and the original ground is scoured by piping. There are several difficulties from the view of construction efficiency and safety. This study finds hydraulic phenomena in final closing construction area, develops a program for final closing simulation, minimizes the error during design and construction, and supports the engineering capacity for efficient and safe construction. The existing design method for final closure only considers the flow in gap, but the developed program considers the seepage in revet and flow in closure gap. This developed program chooses the suitable rock size for final closing design and establishes the proper method for final closing construction.

• Korean Journal of Optics and Photonics
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• v.20 no.3
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• pp.143-147
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• 2009

We propose an asymmetrical 2.5 Gbps / 622 Mbps bidirectional optical subscriber network with Manchester coded downstream and NRZ (Non-Return-to-Zero) upstream remodulation. The proposed system has important characteristics in the optical network unit (ONU): it does not require a light source or the usual control circuits such as wavelength control and output power control, and it is possible to use a synchronization scheme between upstream and downstream data. We theoretically analyze BER(Bit Error Rate) performance of upstream data remodulated with Manchester coded downstream according to the types of NRZ downstream data and perform simulations with MATLAB. The BER performance and the receiver sensitivity have been improved by 3 dB by adjusting threshold levels compared to the conventional receiver. The results have shown the remodulation scheme with Manchester coded downstream could be a useful technology for asynchronous and asymmetric optical subscriber networks with low cost and simple structures.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.9
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• pp.63-69
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• 1998

In this paper, we propose a new Bit-Rate control algorithm based on bit usage matching to substitute encoded GOP(s) for new GOP(s) in MPEG-2 bitstream. It iteratively encodes current picture according to quantization value of previous picture and records bit-usage of each slice until nearly target bits are used. With target bits falling in two output bits, quantization value of slice should be changed to alleviate output bit error. We use recorded bit-usage information to decide which slices should be encoded with one quantization value and others with another. As every macroblock has different activity, we change macroblock quantization value using slice quantization value and activity value. The simulation results demonstrate that the fluctuation of the output bits can be kept within few-several tens of bits while maintaining the quality of the reconstructed pictures at a relatively stable level.

• Journal of Forest and Environmental Science
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• v.33 no.3
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• pp.187-196
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• 2017

The use of unmanned aerial vehicles (UAV) for the estimation of tree height is gaining recognition. This study aims to assess the effectiveness of tree height estimation of Pinus densiflora Sieb. et Zucc. and Pinus koraiensis Sieb. et Zucc. using digital surface model (DSM) generated from UAV-acquired imageries. Images were taken with the $Trimble^{(R)}$ UX5 equipped with Sony ${\alpha}5100$. The generated DSM, together with the digital elevation model (DEM) generated from a digital map of the study areas, were used in the estimation of tree height. Field measurements were conducted in order to generate a regression model and carry out accuracy assessment. The obtained coefficients of determination (R2) and root mean square error (RMSE) for P. densiflora (R2=0.71; RMSE=1.00 m) and P. koraiensis (R2=0.64; RMSE=0.85 m) are comparable to the results of similar studies. The results of the paired two-tailed t-test show that the two tree height estimation methods are not significantly different (p-value=0.04 and 0.10, alpha level=0.01), which means that tree height estimation using UAV imagery could be used as an alternative to field measurement.

• Nuclear Engineering and Technology
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• v.52 no.7
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• pp.1429-1435
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• 2020

Applying an accurate parametric prediction model to identify abnormal or false pressurizer water levels (PWLs) is critical to the safe operation of marine pressurized water reactors (PWRs). Recently, deep-learning-based models have proved to be a powerful feature extractor to perform high-accuracy prediction. However, the effectiveness of models still suffers from two issues in PWL prediction: the correlations shifting over time between PWL and other feature parameters, and the example imbalance between fluctuation examples (minority) and stable examples (majority). To address these problems, we propose a cost-sensitive mechanism to facilitate the model to learn the feature representation of later examples and fluctuation examples. By weighting the standard mean square error loss with a cost-sensitive factor, we develop a Cost-Sensitive Long Short-Term Memory (CSLSTM) model to predict the PWL of PWRs. The overall performance of the CSLSTM is assessed by a variety of evaluation metrics with the experimental data collected from a marine PWR simulator. The comparisons with the Long Short-Term Memory (LSTM) model and the Support Vector Regression (SVR) model demonstrate the effectiveness of the CSLSTM.

• Journal of the Korean Geotechnical Society
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• v.16 no.4
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• pp.95-105
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• 2000

Anisotropy of stiffiness, from extremely small strains to post-failure strains, of isotropically consolidated air-pulviated sands in plane strain compression was studied by using the newly developed instrumentation for small strain measurements. Seven types of sand of the world-wide origins were tested, which have been extensively used for research purposes. Stress-strain relationships for a wide range of strain from about 0.0001% to 10% were obtained with measuring axial and lateral strains locally free from the effects of bedding and membrane penetration errors at the specimen boundaries. It was found that the maximum shear modulus Gmax was irrespective of the angle $\delta$of the $\sigma$1 direction relative to the bedding plane. However, the normalized Gmax was varied with the types of sand. Furthermore, the dependency of the strain and stress level on the stiffness increased as decreased.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.3
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• pp.405-412
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• 2020

The thermistor mount is used for precise RF power measurement because the calibration factor is constant according to the change of power. The calibration factor of the standard mount can be measured with an uncertainty less than 0.5 % from the 10 MHz to 1 GHz by direct comparison with the transfer standard using the DC substitution method. Recently, as the supply of precision power meter based on DC substitution method allows simple and fast measurement, a simple direct comparison measurement system with the same level uncertainty was designed and the minimum required specifications of components through analysis of mismatch error was proposed. The uncertainty was evaluated for system validation, and the results show that uncertainties have been well maintained within 0.5 % in the measurement frequencies.