• Journal of Positioning, Navigation, and Timing
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• 제11권3호
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• pp.191-198
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• 2022

In order to increase the practical use and navigational application performance of the Korean Positioning System (KPS), it is required to provide interoperability with other Global Navigation Satellite System (GNSS). This kind of interoperability can be obtained by broadcasting the time offset between KPS and GNSS using a KPS navigation message. With the assumption that KPS Time (KPST) will be generated by the similar method and equipment of UTC(KRIS), the overall behavior of KPST will be close to that of UTC(KRIS). Therefore, the time offset between KPST and GPS Time (GPST) is estimated by using UTC(KRIS) instead of KPST because KPST can not available at the present time. In this paper, we describe the estimation results of the KPS to GPS Time Offset (KGTO) obtained by using a GNSS time transfer receiver which reference inputs are fed from UTC(KRIS). The estimated KGTO performance is compared to the time offset between UTC(KRIS) and UTC(USNO) which is used to generate GPST and considered as the real GPST. The time offset between UTC(KRIS) and UTC(USNO) is obtained by using the Bureau International des Poids et Mesures (BIPM) Circular T report. From the results, it is observed that KGTO can be estimated under 10 ns with the assumption that KPST will be generated by a similar method of UTC(KRIS) generation.

• 한국지능시스템학회논문지
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• 제11권7호
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• pp.628-632
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• 2001

We propose time-frequency (TF) tools for analyzing linear time-varying (LTV) systems and nonstationary random processes. Obtained warping the narrowband Weyl symbol (WS) and spreading function (SF), the new TF tools are useful for analyzing LTV systems and random processes characterized by generalized frequency shifts, This new Weyl symbol (WS) is useful in wideband signal analysis. We also propose WS an tools for analyzing systems which produce dispersive frequency shifts on the signal. We obtain these generalized, frequency-shift covariant WS by warping conventional, narrowband WS. Using the new, generalized WS, we provide a formulation for the Weyl correspondence for linear systems with instantaneous of linear signal transformation as weighted superpositions of non-linear frequency shifts on the signal. Application examples in signal and detection demonstrate the advantages of our new results.

• 한국군사과학기술학회지
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• 제8권2호
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• pp.38-48
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• 2005

Instantaneous frequency of doppler signals is used to get the information of the relative velocity and the miss distance between a missile and a corresponding target. In this paper, we have performed time-frequency analysis and instantaneous frequency estimation with Short Time Fourier Transform(STFT), Wigner Ville Distribution(WVD) and Continuous Wavelet Transform(CWT) about the doppler signals generated by moving targets. Performance evaluation was performed using simulated doppler signals generated by a single moving target and two moving targets. From the results of the time-frequency analysis, we found that WVD method was the most efficient instantaneous frequency estimator among the three methods. But in case of two moving targets, WVD method got cross talks and CWT method got oscillation when two doppler frequencies were close to each other.

• 한국소음진동공학회논문집
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• 제24권7호
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• pp.569-574
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• 2014

In order to investigate low frequency swishing noise of wind turbines, acoustic source model using a singularity in circular motion is introduced to derive analytic solution of Lowson acoustic analogy in time domain. Results in time and frequency domains computed by the solution show apparent modulation of amplitude and frequency. The solution indicates that time histories of acoustic pressure at receiver points varied significantly according to receiver's directional location, even when the retarded time distributions are similar. However, the corresponding time-averaged spectra of sound pressure at the receiver locations where the retarded time distributions are almost same are not significantly different. It can be inferred from these results that the time-averaged sound pressure spectra which cannot take into account the detailed difference in the time-variation of wind turbine noise may not represent the sound quality of wind turbines due to its swishing. Finally, as an introduction of procedure to quantify low frequency swishing noise level, relative variation of overall sound pressure level is obtained using tonal low frequency noise model.

• 한국수산과학회지
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• 제48권2호
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• pp.221-232
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• 2015

Broadband echoes measured in live chub mackerel Scomber japonicus, goldeye rockfish Sebastes thompsoni, and fat greenling Hexagrammos otakii with different morphologies and internal characteristics were analyzed in time and frequency domains to understand the species-specific echo feature characteristics for classifying fish species. The mean echo image for each time-frequency representation dataset obtained as a function of orientation angle was extracted to mitigate the effect of fish orientation on acoustic scattering. The joint time-frequency content of the broadband echo signals was obtained using the smoothed pseudo-Wigner-Ville distribution (SPWVD). The SPWVDs were analyzed for each echo signature of the three fish species. The results show that the time-frequency analysis provided species-specific echo structure patterns and metrics of the broadband acoustic signals to facilitate fish species classification.

• Smart Structures and Systems
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• 제15권1호
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• pp.81-97
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• 2015

Recently, a new output-only modal identification method based on time-frequency independent component analysis (ICA) has been developed by the authors and shown to be useful for even highly-damped structures. In many cases, it is of interest to identify the complex modes of structures with non-proportional damping. This study extends the time-frequency ICA based method to a complex ICA formulation for output-only modal identification of non-proportionally-damped structures. The connection is established between complex ICA model and the complex-valued modal expansion with sparse time-frequency representation, thereby blindly separating the measured structural responses into the complex mode matrix and complex-valued modal responses. Numerical simulation on a non-proportionally-damped system, laboratory experiment on a highly-damped three-story frame, and a real-world highly-damped base-isolated structure identification example demonstrate the capability of the time-frequency complex ICA method for identification of structures with complex modes in a straightforward and efficient manner.

• Journal of Biosystems Engineering
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• 제26권6호
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• pp.509-516
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• 2001

This paper introduced some advantages of the time-frequency analysis of vibration and investigated, using the time-frequency transform, the characteristics of the transient motion of a tractor seat, which occurred during the tractor traversed over a rectangular obstacle on the flat surface. The characteristics of the short-time courier and wavelet transforms as time-frequency analysis methods were introduced and discussed to figure out which is more suitable to the analysis of the transient motions of agricultural tractors. Using each transform, transient vibration of a tractor seat was analyzed. Results of the analysis showed that the transient vibration of the seat was influenced by the natural frequencies of vertical mode of chassis, pitching mode of engine and pitching mode of cab of the tractor. The time sequence of the natural mode of tractor vibration was also revealed by the time-frequency analysis. The vibration path analysis by the time-frequency transform showed that the vibration energies transmitted from the front mounts to the seat were less than those from the rear mounts. The energy reduction ratios between the cab mounts and seat were also estimated to be about 72∼78%. The front mounts showed larger reduction than the rear mounts. However, the reduction difference between the right and left sides mounts was negligibly small. The short time Fourier transform was found to be a proper method for investigating the transient motions of farm machines and their effects on the ride vibration.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 하계종합학술대회 논문집(5)
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• pp.9-12
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• 2002

The problem of sub-Nyquist nonuniform sampling for the perfect reconstruction of signals with time-varying spectral contents is studied. The signals are assumed to have a known instantaneous bandwidth in time-frequency domain. As the function of time, the nonuniform sampling pattern of a given signal, that is, the instantaneous sampling frequency is determined by the observation of instantaneous bandwidth based on time-frequency analysis. The proposed sampling pattern guarantees the perfect reconstruction of nonuniform sampled signals under Nyquist-sampling rate in average.

• 대한의용생체공학회:의공학회지
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• 제33권3호
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• pp.135-140
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• 2012

Previous investigators have shown that the frequency compression is related to the muscle fatigue and the decreasing conduction velocity of muscle fibers. The aim of the present study was to investigate the relationship between endurance times and frequency parameters such as mean power frequency and median frequency in the surface EMG signal during isotonic contractions. Eight healthy subjects performed voluntary isotonic contractions of biceps Brachii muscle until their endurance times which were determined when the subject could no longer follow the contraction cycle. The regressive slopes of mean power frequency and median frequency were used to describe the frequency compression of the surface EMG signal, and to test the predictability of endurance time. As results of experiment, significant correlations were found between endurance time and the regressive slopes of mean power frequency and mean frequency computed over 50%Tend of endurance time.

• 대한전기학회논문지:시스템및제어부문D
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• 제55권4호
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• pp.181-188
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• 2006

The purpose of this study is to predict the defibrillation success of a ventricular Fibrillation ECG signal using time-frequency analysis. During CPR, coronary perfusion pressure and electrocardiogram were measured. Parameters extracted from time-frequency domain were served as predictor of resuscitation success. Time frequency distribution(TFD) of ECG signals was estimated from the smoothed pseudo Wigner-Ville distribution(SPWVD). Median frequency, peak frequency, 1/f slope, frequency band ratios$(2{\sim}4Hz,\;4{\sim}6Hz,\;6{\sim}8Hz,\;8{\sim}10Hz,\;10{\sim}12Hz,\;12{\sim}15Hz)$ were extracted from each TFD as function of time. Paired t-test was used to determine the differences in ROSC and non-ROSC groups. In the statistical results, we selected four significant parameters - median frequency, 1/f slope, $2{\sim}4Hz$ band ratio, $8{\sim}10Hz$ band ratio. We made an attempt to predict defibrillation success by combining features extracted from time frequency distribution. Independent t-test was used to determine the differences ROSC and non-ROSC groups. Consequently, we selected four significant parameters-median frequency, 1/f slope, $2{\sim}4Hz$ band ratio, $8{\sim}10Hz$ band ratio. The relationship between coronary perfusion pressure and ECG parameters was analyzed with linear regression analysis. R-square value was 55%. 1/f slope and $8{\sim}10Hz$ band ratio had the significant relationship with coronary perfusion pressure.