• Geophysics and Geophysical Exploration
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• v.13 no.3
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• pp.219-226
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• 2010

Current earthquake alert notification for immediate post-earthquake procedures for the critical facilities is exclusively dependent on the ground-motion intensity measures observed at the seismic station located within the site. This practice is prune to false notification due to a noise and problems of missing and poor quality records of the seismic station. The credibility of the earthquake alert notification can be enhanced by utilizing the multiple transformed records of the nearby seismic stations at other sites interconnected to the same earthquake monitoring system by a network. The time-domain transformation of the site-response between the seismic stations is implemented by convoluting the nearby records with a pair of forward and inverse FIR filters designed for the site response relative to a seismic basement. The transformed records from the nearby seismic stations can be used to estimate the ground-motion intensity measures missing at the site or to evaluate the data quality along with other various possible applications in the area of geoscience and earthquake engineering.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.1
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• pp.98-105
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• 2013

This paper presents a finite-difference time-domain(FDTD) simulation and a data processing technique for radar sensing of the internal structure of a wall using an ultra-wide band antenna. We first designed an ultra-wide band anti-podal vivaldi antenna with a frequency range of 0.3~7 GHz which is chosen to be relatively low after considering the characteristics of wave attenuation, wall penetration, and range resolution. In this study the two-dimensional FDTD technique was used to simulate a wall-penetration-radar experiment under practical conditions. The next, the measured radiation pattern of the practical antenna is considered as an equivalent source in the FDTD simulation, and the reflection data of a concrete wall and targets are obtained by using the simulation. Then, a data processing technique has been applied to the FDTD reflection data to get a radar image for remote sensing of the internal structure of the wall. We compared the two different source excitations in the FDTD simulation; (1) commonly-used isotropic point sources and (2) polynomial curve fitting sources of the measured radiation pattern. As a result, when we apply the measured antenna pattern into the FDTD simulation, we could obtain about 2.5 dB higher signal to noise level than using a plane wave incidence with isotropic sources.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.7
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• pp.151-157
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• 2019

Recently, monitoring respiration of people has been of interest using non-invasive method. Among the vital signals usually used for indicating health status, non-invasive and portable device based monitoring respiratory status is practically useful and enable one to promptly deal with abnormal physical status. This paper proposes the approach to real-time detection of apnea signal based on Short-Time-Fourier-Transform(STFT). Contrary to the analysis of a signal in frequency domain using Fast-Fourier Transform, this paper employs Short-time-Fourier-Transform so that frequency response can be analyzed in short time interval. The respiratory signal is acquired using UWB radar sensor that enables one to obtain respiration signal in contactless way. Detection of respiratory status is carried out by analyzing frequency response, and classification of respiratory status can be provided. In particular, STFT is employed to analyze respiratory signal in real-time, leading to effective analysis of the respiratory status in practice. In the case of existence of noise in the signal, appropriate filtering process is employed as well. The proposed method is straightforward and is workable in practice to analyze the respiratory status of people. To evaluate the proposed method, experimental results are provided.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.2
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• pp.123-129
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• 2017

This paper proposes a new nonnegative matrix factorization (NMF) based direction-of-arrival (DOA) estimation method for multiple sound sources using a dual microphone array. First of all, sound signals coming from the dual microphone array are segmented into consecutive analysis frames, and a steered-response power phase transform (SRP-PHAT) beamformer is applied to each frame so that stereo signals of each frame are represented in a time-direction domain. The time-direction outputs of SRP-PHAT are stored for a pre-defined number of frames, which is referred to as a time-direction block. Next, In order to estimate DOAs robust to noise, each time-direction block is normalized along the time by using a block subtraction technique. After that, an unsupervised NMF method is applied to the normalized time-direction block in order to cluster the directions of each sound source in a multiple sound source environments. In particular, the activation and basis matrices are used to estimate the number of sound sources and their DOAs, respectively. The DOA estimation performance of the proposed method is evaluated by measuring a mean absolute error (MAE) and the standard deviation of errors between the oracle and estimated DOAs under a three source condition, where the sources are located in [$-35{\circ}$, 5m], [$12{\circ}$, 4m], and [$38{\circ}$, 4.m] from the dual microphone array. It is shown from the experiment that the proposed method could relatively reduce MAE by 56.83%, compared to a conventional SRP-PHAT based DOA estimation method.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.1
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• pp.6-12
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• 2010

Fiber optic sensor using fiber Bragg grating(FBG) probes is used for monitoring strain and temperature distributed on the wide surfaces of large structures. In this paper, in order to use many FBG probes in one optical fiber line, we propose a complex multiplexing technology which is composed of two techniques, one is time division multiplexing and another is wavelength division multiplexing. However, we only investigate the characteristics of time division multiplexing because FBG sensors basically can be operated by wavelength division multiplexing. We calculate the optimal reflectivities and the lengthwise location of five FBG probes in serial connection in order to obtain the unique reflected intensities from the FBG probes. We fabricate five FBG probes with the reflectivities of 13%, 16%, 25%, 40% and 80%, which are determined by the theoretical calculation, and observe the signal reflected from each FBG in the time domain from the experiment. There are differences between experimental and theoretical results caused by the signal noise and the differences of reflectivities of FBG probes. But the experimental results shows the reflected signals of five FBG probes which prove the availability of complex multiplexing.

• Smart Structures and Systems
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• v.24 no.6
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• pp.769-781
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• 2019

Dynamic displacement response of civil structures is an important index for in-construction and in-service structural condition assessment. However, accurately measuring the displacement of large-scale civil structures such as high-rise buildings still remains as a challenging task. In order to cope with this problem, a vision-based system with the use of industrial digital camera and image processing has been developed for long-distance, remote, and real-time monitoring of dynamic displacement of supertall structures. Instead of acquiring image signals, the proposed system traces only the coordinates of the target points, therefore enabling real-time monitoring and display of displacement responses in a relatively high sampling rate. This study addresses the in-situ experimental verification of the developed vision-based system on the Canton Tower of 600 m high. To facilitate the verification, a GPS system is used to calibrate/verify the structural displacement responses measured by the vision-based system. Meanwhile, an accelerometer deployed in the vicinity of the target point also provides frequency-domain information for comparison. Special attention has been given on understanding the influence of the surrounding light on the monitoring results. For this purpose, the experimental tests are conducted in daytime and nighttime through placing the vision-based system outside the tower (in a brilliant environment) and inside the tower (in a dark environment), respectively. The results indicate that the displacement response time histories monitored by the vision-based system not only match well with those acquired by the GPS receiver, but also have higher fidelity and are less noise-corrupted. In addition, the low-order modal frequencies of the building identified with use of the data obtained from the vision-based system are all in good agreement with those obtained from the accelerometer, the GPS receiver and an elaborate finite element model. Especially, the vision-based system placed at the bottom of the enclosed elevator shaft offers better monitoring data compared with the system placed outside the tower. Based on a wavelet filtering technique, the displacement response time histories obtained by the vision-based system are easily decomposed into two parts: a quasi-static ingredient primarily resulting from temperature variation and a dynamic component mainly caused by fluctuating wind load.

• Journal of Broadcast Engineering
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• v.27 no.2
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• pp.244-247
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• 2022

In this paper, the performance of the decoding schemes using linear MMSE filters in the frequency and time domains and the reinforcement Gauss-Seidel algorithm for the orthogonal time frequency space (OTFS) system that can improve robustness under high-speed mobile environments are compared. The reinforcement Gauss-Seidel algorithm can improve the bit error rate performance by suppressing the noise enhancement. The simulation results show that the performance of the decoding scheme using the linear MMSE filter in the frequency domain is severely degraded due to the effect of Doppler shift as the mobile speed increases. In addition, the decoding scheme using the reinforcement Gauss-Seidel algorithm under the channel environment with 120 km/h and 500 km/h speeds outperforms the decoding schemes using linear MMSE filters in the frequency and time domains.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.5
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• pp.558-565
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• 2013

In this paper, modeling and simulation for performance analysis of high resolution SAR system has been carried out in the time, frequency and numeric domain using ADS Ptolemy simulation tool of Agilent corporation. SAR system consists of antenna, controller and transceiver. Error parameters affecting SAR system performances have been defined, modeled and simulated such as phase noise of frequency synthesizer, amplitude and phase characteristic of TWTA, sampling frequency of waveform generator and I/Q imbalance. Finally, the development requirements of SAR system based on the impulse response function have been derived.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.10
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• pp.1755-1760
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• 2016

Automation of greenhouses has proved to be extremely helpful in maximizing crop yields and minimizing labor costs. The optimum conditions for cultivating plants are regularly maintained by the use of programmed sensors and actuators with constant monitoring of the system. In this paper, we have designed a prototype of a smart greenhouse using Arduino microcontroller, simple yet improved in feedbacks and algorithms. Only three important microclimatic parameters namely moisture level, temperature and light are taken into consideration for the design of the system. Signals acquired from the sensors are first isolated and filtered to reduce noise before it is processed by Arduino. With the help of LabVIEW program, Time domain analysis and Fast Fourier Transform (FFT) of the acquired signals are done to analyze the waveform. Especially, for smoothing the outlying data digitally, Moving average algorithm is designed. With the implement of this algorithm, variations in the sensed data which could occur from rapidly changing environment or imprecise sensors, could be largely smoothed and stable output could be created. Also, actuators are controlled with constant feedbacks to ensure desired conditions are always met. Lastly, data is constantly acquired by the use of Data Acquisition Hardware and can be viewed through PC or Smart devices for monitoring purposes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.1B
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• pp.66-78
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• 2002

In this paper, we propose a new symbol offset estimation technique for an orthogonal frequency-division multiplexing (OFDM)-based wireless LAN. When both inter-symbol interference (ISI) and inter-channel interference (ICI) do not exist in an OFDM symbol, symbol offsets cause circular shifts in the estimated channel impulse response (CIR) by the amount of symbol offset. Also, the power delay profile of a typical multipath wireless channel can be modeled by exponentially decaying function, and most energy of multipath channel is concentrated at the beginning part of the CIR. Based on these properties, the proposed symbol offset estimation technique estimates the CIR, which is circularly shifted by the amount of symbol offset, and then calculates the partial mean power from the estimated impulse response by using a moving window with a finite length. And, symbol offset can be estimated from the index of a moving window having the maximal partial mean power. The proposed technique can reduce noise effect in the process of the CIR estimation, and remove ISI and ICI using repetitive training symbol structure in time-domain for minimum training overhead. The performances of the proposed symbol offset estimation technique in typical indoor channels are demonstrated by computer simulation.