• Proceedings of the KIEE Conference
• /
• 2005.07a
• /
• pp.211-213
• /
• 2005

In this paper, the frequency compensator for digital protective relay is introduced. Due to sudden appearance of generation-load or fault in power system, the frequency can deviate from its nominal value. The Orthogonal filter adopted to digital protective relay is exposed to the problem. Therefore, the frequency variation makes a difficult to protective function and power measurement in digital protective relay. The essential property of the proposed algorithm presented is its outstanding immunity to both signal orthogonal component magnitudes and DFT filter gain variations which ensures below 0.05Hz accuracy of estimation. Additionally, the proposed method has excellent characteristics with low signal sampling rate. Based on the frequency estimation, author design under frequency protection relay for generator and verifies its performance with several experimental tests.

• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.55 no.6
• /
• pp.249-254
• /
• 2006

A new algorithm for estimating power frequency is presented. Unlike conventional algorithms, the proposed algorithm is based on the fact that the magnitude gains of cosine and sine filters become different when the power frequency is deviated from the nominal value. This makes the algorithm capable of providing an accurate and fast estimate of the power frequency. To demonstrate the performance of the developed algorithm, various computer simulated data records are processed. The algorithm showed a high level of robustness as well as high measurement accuracy over a wide range of frequency changes. Moreover, the algorithm was highly immune to harmonics and noise.

• Proceedings of the Acoustical Society of Korea Conference
• /
• spring
• /
• pp.209-212
• /
• 2002

The wear process of end mill is a so complicated process that a more reliable technique is required for the monitoring and controling the tool life and its performance. This research presents a new tool wear monitoring method based on the sound signal generated on the machining. The experiment carried out continuous-side-milling for 4 cases using the high-speed steel slot drill under wet condition. The sound pressure was measured at 0.5m from the cutting zone by a dynamic microphone, and was analyzed at frequency domain. The tooth passing frequency appears as a harmonics form, and end mill wear is related with the first harmonic. It can be concluded from the result that the tool wear is correlate with the intensity of the measured sound at tooth passing frequency estimation of end mill wear using sound is possible through frequency analysis at tooth passing frequency under the given circumstances.

• The Journal of the Acoustical Society of Korea
• /
• v.18 no.2E
• /
• pp.39-44
• /
• 1999

In passive sonar, underwater moving objects are identified by the acoustic sounds they transmit. The spectrum of these sounds show features about the mechanism of the sound source, these features are discrete frequencies on the spectrum and frequency lines on the spectrogram. Variability in the underwater environment produce discontinuous broken or unstable fluctuating frequency lines. In this paper, we propose an efficient algorithm that estimate continuities of the discontinuous frequency lines and extract presence of the unstable frequency lines using neural networks and represent the proposed algorithm shows good performance in estimation and extraction the unstable frequency lines through the experiments.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.6A
• /
• pp.640-650
• /
• 2004

Channel estimation schemes are proposed for Multiple Input-Multiple output Orthogonal Frequency Division Multiplexing(MIMO-OFDM) systems based on the physical layer specification of the IEEE 802.1 la. By combining the space-time block coding(STBC)/ space-frequency block coding(SFBC) techniques with the transform domain interpolation, the proposed algorithms achieve more accurate channel coefficients for the MIMO channels such that improve the BER performance. The performance improvements of the proposed algorithms are evaluated by simulations under the various multipath fading channel environments and various transmission rates.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.30 no.9A
• /
• pp.781-787
• /
• 2005

In this paper, an estimation method of intercell carrier frequency-offset(CFO) in orthogonal frequency division multiplexing(OFDM)-based cellular systems is proposed for a user's equipment(UE), especially at the cell boundary, in downlink channels. Also, after deriving an estimation method of intercell CFO from the signals received by adjacent base stations(BSs), we propose a cell-searching method using the estimated CFOs. It is shown by computer simulation that the proposed methods can uniquely estimate the intercell CFOs and identify the target BS with a high detection probability.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2014.10a
• /
• pp.713-717
• /
• 2014

This paper presents a beamforming technique for locating impulsive sound source. The conventional frequency-domain beamformer is advantageous for localizing noise sources for a certain frequency band of concern, but the existence of many frequency components in the wide-band spectrum of impulsive noise makes the beamforming image less clear. In contrast to a frequency-domain beamformer, it has been reported that a time-domain beamformer can be better suited for transient signals. Although both frequency- and time-domain beamformers produce the same result for the beamforming power, which is defined as the RMS value of its output, we can use alternative directional estimators such as the peak value and crest factor to enhance the performance of a time-domain beamformer. In this study, the performance of three different directional estimators, the peak, crest factor and RMS output values, are investigated and compared with the incoherent interfering noise embedded in multiple microphone signals. The proposed formula is verified via experiments in an anechoic chamber using a uniformly spaced linear array. The results show that the peak estimation of beamformer output determines the location with better spatial resolution and a lower side lobe level than crest factor and RMS estimation in noise free condition, but it is possible to accurately estimate the direction of the impulsive sound source using crest factor estimation in noisy environment with stationary interfering noise.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.28 no.11C
• /
• pp.1111-1117
• /
• 2003

The maximum Doppler frequency, or equivalently, the mobile speed is very useful information to optimize the performance of many wireless communication systems. However, the performance of a maximum Doppler frequency estimator is limited since it requires an estimate of the signal-to-noise ratio (SNR) of the channel environment. In this paper, the improved method for the maximum Doppler frequency estimations based on the decision feedback Doppler adaptive band-limit (DF-DABL) method is proposed. To reduce the effect of additive noise, the proposed algorithm uses a novel Doppler adaptive band-limit (DABL) technique. The distortion due to the additive noise is drastically removed by the proposed DF-DABL method. Especially, the DF-DABL method does not need any other channel information such as SNR.

• Speech Sciences
• /
• v.12 no.4
• /
• pp.53-70
• /
• 2005

A Vowel of speech signals are multicomponent signals composed of AM-FM components whose instantaneous frequency and instantaneous amplitude are time-varying. The changes of emotion states cause the variation of the instantaneous frequencies and the instantaneous amplitudes of AM-FM components. Therefore, it is important to estimate exactly the instantaneous frequencies and the instantaneous amplitudes of AM-FM components for the extraction of key information representing emotion states and changes in speech signals. In tills paper, firstly a method decomposing speech signals into AM - FM components is addressed. Secondly, the fundamental frequency of vowel sound is estimated by the simple method based on the spectrogram. The estimate of the fundamental frequency is used for decomposing speech signals into AM-FM components. Thirdly, an estimation method is suggested for separation of the instantaneous frequencies and the instantaneous amplitudes of the decomposed AM - FM components, based on Hilbert transform and the demodulation property of the extended Fourier transform. The estimates of the instantaneous frequencies and the instantaneous amplitudes can be used for modification of the spectral distribution and smooth connection of two words in the speech synthesis systems based on a corpus.

• Journal of Biomedical Engineering Research
• /
• v.28 no.1
• /
• pp.84-94
• /
• 2007

In order to collect information on local distribution of conductivity and permittivity underneath a scan probe, we developed a multi-frequency trans-admittance scanner (TAS). Applying a sinusoidal voltage with variable frequency on a chosen distal part of a human body, we measure exit currents from 320 grounded electrodes placed on a chosen surface of the subject. The electrodes are packaged inside a small and light scan probe. The system includes one voltage source and 17 digital ammeters. Front-end of each ammeter is a current-to-voltage converter with virtual grounding of a chosen electrode. The rest of the ammeter is a voltmeter performing digital phase-sensitive demodulation. Using resistor loads, we calibrate the system including the scan probe to compensate frequency-dependent variability of current measurements and also inter-channel variability among multiple. We found that SNR of each ammeter is about 85dB and the minimal measurable current is 5nA. Using saline phantoms with objects made from TX-151, we verified the performance of the lesion estimation algorithm. The error rate of the depth estimation was about 19.7%. For the size estimate, the error rate was about 15.3%. The results suggest improvement in lesion estimation algorithm based on multi-frequency trans-admittance data.