• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2006.11a
• /
• pp.502-505
• /
• 2006

Acoustic holography allows us to predict spatial pressure distribution on any surface of interest from measured hologram. It is noteworthy that the data size is so huge that it takes long time to calculate pressure field. Moreover the reconstructed pressure field is frequently too complicated to get what we want to know. One possible candidate is complex envelope. Complex envelope in time domain is well known and widely used in various engineering field. We have attempted to extend this method to space domain, so that we can have rather simple spatial pressure picture that provides information we need, for example, where sound sources are. First we start with the simplest case. We examine the complex envelope of a plane wave on both space and wave number domain. Then we extend to monopole case. Holographic reconstructed sound field on the monopole is processed according to what we propose. We demonstrate how this method provides better picture for analyzing the sound field.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.58 no.2
• /
• pp.136-141
• /
• 2009

An AC generator is an important components in producing a electric power and so it requires highly reliable protection relays to minimize the possibility of demage occurring under fault conditions. Conventionally, a DFT based RDR has been used for protecting the generator stator winding. However, when DFTs based on Fourier analysis are used, it has been pointed out that defects can occur during the process of transforming a time domain signal into a frequency domain one which can lead to loss of time domain information. This paper proposes the internal fault detection and fault type discrimination for the stator winding by applying the detailed coefficients by Daubechies Wavelet Transform to overcome the defects in the DFT process. For the case studies reported in the paper, a model system was established for the simulations utilizing the ATP, and this verified the effectiveness of the proposed technique through various off-line tests carried out on the collected data. The propose method is shown to be able to rapidly identify internal fault and did not operate a miss-operation for all the external fault tested.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.10 no.6
• /
• pp.2446-2462
• /
• 2016

In this paper, a frequency domain Expectation-Maximization (EM)-based channel estimation algorithm for Space Time Block Coded-Orthogonal Frequency Division Multiplexing (STBC-OFDM) systems is investigated to support higher data rate applications in wireless communications. The computational complexity of the frequency domain EM-based channel estimation is increased when higher order constellations are used because of the ascending size of the search set space. Thus, a search set reduction algorithm is proposed to decrease the complexity without sacrificing the system performance. The performance results of the proposed algorithm is obtained in terms of Bit Error Rate (BER) and Mean Square Error (MSE) for 16QAM and 64QAM modulation schemes.

• Journal of electromagnetic engineering and science
• /
• v.18 no.3
• /
• pp.212-214
• /
• 2018

The finite-difference time-domain (FDTD) model was developed to analyze electromagnetic (EM) wave propagation in an inhomogeneous ionosphere. The EM analysis of ionosphere is complicated, owing to various propagation environments that are significantly influenced by plasma frequency, cyclotron frequency, and collision frequency. Based on the simple auxiliary differential equation (ADE) technique, we present an accurate FDTD algorithm suitable for the EM analysis of complex phenomena in the ionosphere under arbitrary-direction geomagnetic field. Numerical examples are used to validate our FDTD model in terms of the reflection coefficient of a single magnetized plasma slab. Based on the FDTD formulation developed here, we investigate EM wave propagation characteristics in the ionosphere using realistic ionospheric data for South Korea.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.7C
• /
• pp.954-961
• /
• 2004

In this paper, we propose a STF(Space-Time-Frequency) coded OFDM(Orthogonal Frequency Division Multiplexing) transmission scheme as an attractive solution for high bit rate data transmission in a multipath fading environment. The STF-OFDM transmission scheme that we propose in this paper is a simple transmission cheme for achieving frequency diversity gain with low complexity. Using preceding in frequency domain, we obtain frequency diversity gain and improve the SER performance of conventional ST-OFDM. The preceding scheme proposed in this paper is a very simple method that can be encoded and decoded with low complexity.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.33 no.12
• /
• pp.1442-1448
• /
• 2009

Transient characteristics of a signal can be effectively exhibited in time-frequency domain. Hilbert-Huang Transform (HHT) is one of the time-frequency domain analysis methods. HHT is known for its several advantages over other signal analysis methods. The capability of analyzing non-stationary or nonlinear characteristics of a signal is the primary advantage of HHT. Moreover, it is known that HHT can provide fine resolution in high frequency region and handle large size data efficiently. In this study, the effectiveness of Hilbert-Huang transform is illustrated by employing structural systems undergoing impact. A simple discrete system and an axially oscillating cantilever beam undertaking periodic impulsive force are chosen to show the effectiveness of HHT.

• 제어로봇시스템학회:학술대회논문집
• /
• 2000.10a
• /
• pp.547-547
• /
• 2000

Recently, due to the advance of computer, network and Internet technology, control/monitoring systems are required to process the massive data, At the same time, the software development environment uses more and more component-based methodology. This paper proposes the services for the control /monitoring domain. Especially we define domain-specific interfaces and categories to acquire compatibility between products, and implement architecture for lightweight event service. As it is very important to support compatibility between heterogeneous systems, the proposed system provides modules for the web service and communication protocols based on the XML. And as proposed architecture consists of cluster of servers and Windows 2000's NLB service, it can guarantee more stable operation,

• Journal of the Optical Society of Korea
• /
• v.13 no.3
• /
• pp.367-372
• /
• 2009

In this paper we propose an electronic domain timing phase selection scheme for the optical communication systems suffering from inter-symbol-interference (ISI) distortion due to chromatic dispersion (CD) or polarization mode dispersion (PMD). In the presence of CD/PMD a proper timing phase selection is important for discrete time domain equalizers, since different timing phases produce different nonlinear ISI channels of different severity. The proposed timing phase recovery scheme based on dispersion minimization (DM) practically approximates the optimal minimum mean squared error (MMSE) timing phase without training signals which reduces overall throughput substantially, especially in time-varying channels such as PMD. The simulation results show that the proposed DM timing agrees with MMSE timing phase, under proper normalization of the received signals, for various dispersion and OSNR.

• Journal of Families and Better Life
• /
• v.17 no.1
• /
• pp.167-178
• /
• 1999

The purpose of this study were to 1) classify the domain according to the level f housework sociaklization and 2) illuminate the determinants on it. The subjects of this study were 564 married women living in Seoul. A questionnaire was used as survey method. Frequenciaes percentiles mean and regression were employed for data analysis. major findings were as follows; 1) The domain according to the level of housework socialization were purchases of storage food convemience food dining-out clothes repairing services and laundry wervices 2) Of market goods characteristics quality and time-saving characteristics were influencing variables in the level of storage food purchases. The affecting variables in the level of convenience food purchases dining-out and clothes repairing services purchases was quality of market goods. In the level of laundry services time-saving characteristics was significant.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2000.10a
• /
• pp.18-23
• /
• 2000

The radar method is becoming one of the major nondestructive testing (NDT) techniques for concrete structures. Numerical modeling of electromagnetic wave is needed to analyze radar measurement results and to study the influence of measurement parameters on the radar measurements. Finite difference-time domain (FD-TD) method is used to simulate electromagnetic wave propagation through concrete specimens. Three concrete specimens with a 19.1 mm rebar embedded at 40 mm, 60 mm, and 80 mm depth are modeled in 3-dimension. As results, 2-D image processing scheme of modeling data has been developed and applied to the imaging of steel bars inside concrete.