• Journal of Electrical Engineering and Technology
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• 제9권4호
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• pp.1210-1216
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• 2014

This paper deals with an application of Teager Energy Operator (TEO) and Energy Separation Algorithm(ESA) to detect and determine various voltage waveform distortions like harmonics, inter-harmonics and frequency variation. Because the TEO and DESA algorithm was initially proposed for speech or communication analysis, its applications are limited to some types of waveform in the power quality analysis area. For example, an undistorted voltage signal is similar with a pure sinusoid. A voltage fluctuation is very similar with an amplitude-modulated signal, from the viewpoint of signal theory. And a continuous frequency variation is similar with a frequency-modulated signal, which is also known as a chirp signal. This paper is written to show that the TEO and DESA algorithm can be used for detecting occurrences of the representative waveform distortions and determining their instantaneous information of amplitude and frequency.

• The Transactions of the Korean Institute of Electrical Engineers D
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• 제54권9호
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• pp.521-530
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• 2005

In this paper, a new high resolution reflectometry scheme, time-frequency domain reflectometry(TFDR), isproposed to detect and estimate a fault in a transmission line. Traditional reflectometry methodologies have been achieved either in the time domain or in the frequency domain only. However, the TFDR can jump over the performance limits of the traditional reflectometry methodologies because the acquired signal is analyzed in time and frequency domain simultaneously. In the TFDR, the new reference signal and the novel TFDR algorithm are proposed for analyzing the acquired signal in the time-frequency domain. Because the reference signal of Gaussian envelop chirp signal is localized in the time and frequency domain simultaneously, it is suitable to the analysis in the time-frequency domain. In the proposed TFDR algorithm, the time-frequency distribution function and the normalized time-frequency cross correlation function are used to detect and estimate a fault in a transmission line. That algorithm is verified for real-world coaxial cables which are typical transmission line with different types of faults by the TFDR system composed of real instruments. The performance of the TFDR methodology is compared with that o( the commercial time domain reflectomeoy(TDR) experiments, so that concludes the TFDR methodology can detect and estimate the fault with smaller error than TDR methodology.

• Journal of Electrical Engineering and Technology
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• 제5권3호
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• pp.497-502
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• 2010

In this paper, the O-mode ultrashort-pulse reflectometry (USPR) millimeter-wave signals that propagate into the plasma and cover a frequency bandwidth of 33-158 GHz are examined numerically using MATLAB. Two important processes are involved in the computation: the propagation of the USPR impulse signal through a waveguide and the frequency up-conversion using millimeter-wave mixers. These mixers are limited to intermediate frequency signals that are less than 500 mV; thus, it is necessary to disperse the impulse signal into a chirped waveform using the waveguide. The stationary phase method is utilized to derive a closed-form formula for a chirped waveform under the assumption that the USPR impulse is Gaussian. In the process of frequency up-conversion, the chirped waveform is mixed with the mixer LO signal, and the lower frequency components of the RF signal are removed using high pass filters.

• Journal of Institute of Control, Robotics and Systems
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• 제16권7호
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• pp.720-725
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• 2010

In AGPS method, user position can be obtained even in the shadow region by improving signal sensitivity. A hybrid long integration scheme employing both coherent and non-coherent integration method is commonly used in AGPS receivers. Because coherent loss increases as residual frequency become large, residual frequency should be minimized to maximize coherent integration gain. This paper presents performance analysis of residual frequency estimator using FFT in fine-time assistance AGPS method. Considering the hardware complexity and the estimation accuracy, optimal length of FFT is proposed for GPS L1 C/A signal. Signal sensitivity for estimating the residual frequency is also analysed. By field experimental results, it is found that the residual frequency can be successfully estimated using 1 second snap-shot data when GPS signal strength is larger than -150 dBm and its RMS error is 3Hz.

• Journal of Environmental Science International
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• 제24권3호
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• pp.353-358
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• 2015

In this study, we analyzed two types of echolocation calls used by the parti-coloured bat, Vespertilio sinensis. Bats were captured in the Naejangsan National Park in October 2013. Call sounds of hand-released bats were recorded at the location of capture within the National Park. We analyzed pulse duration (PD), pulse interval (PI), peak frequency (PF), maximum frequency ($F_{MAX}$), minimum frequency ($F_{MIN}$), and bandwidth (BW). V. sinensis emitted the different types of the echolocation calls depending on the surrounding environment. Frequency modulated-constant frequency (FM-CF) signal of audible range was emitted when they flew in the uncluttered space over the canopy. However, when flying in the cluttered space below the canopy, they only emitted FM signal. FM-CF signal is in the audible range (e.g., low frequency), and FM signal has a harmonic broadband frequency range of two. There were significant differences in PD, PI, PF, FMAX, FMIN, and BW between the calls emitted over and below the canopy. Considering the functional characteristics of FM and CF signals, we conclude that the foraging activity of V. sinensis was observed below the canopy, and recommend the use of FM signal and broadband as echolocation signals.

• Journal of the Korean Institute of Telematics and Electronics
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• 제12권6호
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• pp.1-4
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• 1975

This paper dells with the impedance variations of the IMPATT diode depending upon the small a.c. coomponent superimposed on the d.c. bias. The frequency deviation of the modulated wave is measured using a carrier null method on microwave spectrum analyser. Frequency modulation is achieved by the weack a.c. signal superimposed on the d.c. bias. The bandwidth rapidly increase with increasing modulation signal magnitude for constant modulation frquency and slightly decrease with decreasing modulation frequency for constant modulation signal magnitude.

• Transactions of the Korean Society of Mechanical Engineers
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• 제18권4호
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• pp.1050-1056
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• 1994

When a vibration data for a rotating machine such as a pump or a compressor is concerned, the frequency fluctuation of the energy contents at an instant time may provide useful information on understanding the vibration characteristics of the rotating machinery, rather than the averaged energy distribution along the frequency axis. Especially, when a periodic signal has different spectral contents, the approach to use the averaged frequency distribution, called the normal frequency analysis, may not be appropriate to extract vibration source characteristics of the structure. This paper introduces a way to analyze the signal based on an instant time. In order to evaluate the performance of the various approach, the investigatation compares three different algorithms which are frequently implemented in the instantaneous frequency analysis. Also for the noise effect embodied in the true signal, various cases for different SN ratio have been examined. The result shows that the noise level is crucial to evalute the instantaneous frequency analysis. In order to implement the instantaneous frequency analysis, the extraction of the relevant information from the measured signal should have the high S/N ratio, i, e., 40 dB or above.

• Transactions of the Korean Society of Mechanical Engineers
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• 제18권4호
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• pp.1057-1063
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• 1994

An instantaneous frequency analysis is a technique to examine a signature for the rotating machinery if the signal has several transitions within a cycle. This paper discusses the conditions of existing negative frequency components in the instantaneous frequency. By using a signal consisted of two frequency components, the instantaneous frequency analysis is conducted while the amplitude ratio between two frequency components has been changed. The analysis shows that, depending on the amplitude ratio, the instantaneous frequencies have averaged, zero-valued, or negative components. It turns out that the negative-valued instantaneous frequencies, which have been regarded as the noise effect, are the consequence of the calculation process for the multisignal components. The criteria of existing the negative values in instantaneous frequencies is given in terms of the relative amplitude ratio and the frequency difference. Especially when the amplitude ratio approaches to 1, the instantaneous frequency fluctuates ${\pm}\infty$ in theory, which implies that instantaneous frequency has unstable region around the amplitude ratio, 1.Also, as the frequency difference between major signal components is increased, the region of existing negative instantaneous becomes broader. In an instantaneous frequency analysis, therefore, a narrow band analysis is suggested, with extreme care if the amplitude ratio approaches to 1. In this paper, a vibration signal monitored from a rotating machinery is also examined as an application example in order to show the existence of negative instantaneous frequencies components.

• Proceedings of the IEEK Conference
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• 대한전자공학회 1998년도 추계종합학술대회 논문집
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• pp.1183-1186
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• 1998

Adaptive nois canceller can extract the noiseremoved spech in noisy speech signal by adapting the filter-coefficients to the background noise environment. A kind of LMS algorithm is one of the most popular adaptive algorithm for noise cancellation due to low complexity, good numerical property and the merit of easy implementation. However there is the matter of increasing misadjustment at voiced speech signal. Therefore the demanded speech signal may be extracted. In this paper, we propose a fast and noise robust wavelet packet adaptive noise canceller with NLMS-SUM method LMS combined algorithm. That is, we decompose the frequency of noisy speech signal at the base of the proposed analysis tree structure. NLMS algorithm in low frequency band can efficiently dliminate the effect of the low frequency noise and SUM method LMS algorithm at each high frequency band can remove the high frequency nosie. The proposed wavelet packet adaptive noise canceller is enhanced the more in SNR and according to Itakura-Satio(IS) distance, it is closer to the clean speech signal than any other previous adaptive noise canceller.

• Proceedings of the Acoustical Society of Korea Conference
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• 한국음향학회 1994년도 FIFTH WESTERN PACIFIC REGIONAL ACOUSTICS CONFERENCE SEOUL KOREA
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• pp.674-679
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• 1994

Acoustic signal such as speech and scattered sound, are generally a nonstationary process whose frequency contents vary at any instant of time. For time-varying signal, whether a nonstationary or a deterministic transient signal, a traditional frequency domain representation does not reveal the contents of signal characteristics and may lead to erroneous results such as the loss of desired characteristics features or the mis-interpretation for a wrong conclusion. A time-frequency domain representation is needed to characterize such signatures. Pseudo Wigner-Ville distribution (PWVD) is ideally suited for portraying nonstationary signal time-frequency domain and carried out by adapting the fast Fourier transform algorithm. In this paper, the important properties of PWVD were investigated using both stationary and nonstationry signatures by numerical examples PWVD was applied to acoustic sigtnatures to demonstrate its application for time-ferquency domain analysis.