• ETRI Journal
• /
• v.37 no.1
• /
• pp.1-10
• /
• 2015

A blind hopping phase estimator is proposed for the demodulation of received signals in frequency-hopping spread spectrum systems. The received signals are assumed to be bandwidth limited with a shaping filter, modulated as frequency modulation (FM) or binary frequency shift keying (BFSK), and hopped by predetermined random frequency sequences. In the demodulation procedure in this paper, the hopping frequency tracking is accomplished by choosing a frequency component with maximum amplitude after taking a discrete Fourier transform, and the hopping phase estimator performs the conjugated product of two consecutive signals and moving-average filtering. The probability density function and Cramer-Rao low bound (CRLB) of the proposed estimator are evaluated. The proposed scheme not only is very simple to implement but also performs close to the CRLB in demodulating hopped FM/BFSK signals.

• Journal of the Optical Society of Korea
• /
• v.18 no.5
• /
• pp.449-452
• /
• 2014

We present a multi-tap microwave photonic filter with high selectivity through applying time-to-frequency mapping and optical frequency comb shaping techniques. When arranged in the time-to-frequency mapping stage, by a Fourier transform, the deviation of the optical taps to the target profile is significantly reduced while maintaining the apodization profile, resulting in high sidelobe suppression in the filters. By applying a simple time-to-frequency mapping stage to the conventional optical frequency combs, we demonstrate a substantially enhanced (>10dB) sidelobe suppression, resulting in filter lineshapes exhibiting a significantly high (>40dB) main lobe to sidelobe suppression ratio. These results highlight the potential of the technique for implementation in various passband filters with high sidelobe suppression.

• Tunnel and Underground Space
• /
• v.15 no.5 s.58
• /
• pp.352-358
• /
• 2005

For non-destructive testing of concrete structures, time and frequency domain method were applied to detect cavity in underground model and pier model. To interpret the measured data, time domain method made use of tomography which was completed with first arrivaltime and inversion method. In this steady, frequency domain method using Fourier transform was tried. Maximum frequency in the frequency domain was analyzed to calculate location of cavity.

• Journal of the Institute of Electronics Engineers of Korea SC
• /
• v.44 no.6
• /
• pp.29-34
• /
• 2007

It is important to analyse the frequency spectrum for the measurement of modulated signal, distortion, and noise. The frequency spectrum analysis is performed by the execution of Radix-2 DIT DFT i.e. FFT algorithm. The discrete input signal converted by A/D converter from the input signal in time domain is mathematically transformed to the frequency spectrum by FFT algorithm. In this study, we design the digital spectrum analyser by the hardware based on the TMS320F2812 DSP and AD9244 converter, and by the software based on the C28x S/W modules. We can timely analyse the frequency spectrum in mobile communication system by the digital frequency analyser based on the high performance DSP and S/W modules. This real-time analysing capability is the important performance in the internet-based mobile communication server system.

• Journal of Intelligence and Information Systems
• /
• v.5 no.1
• /
• pp.103-123
• /
• 1999

Input filtering as a preprocessing method is so much crucial to get good performance in time series forecasting. There are a few preprocessing methods (i.e. ARMA outputs as time domain filters, and Fourier transform or wavelet transform as time-frequency domain filters) for handling time series. Specially, the time-frequency domain filters describe the fractal structure of financial markets better than the time domain filters due to theoretically additional frequency information. Therefore, we, first of all, try to describe and analyze specially some issues on the effectiveness of different filtering methods from viewpoint of the performance of a neural network based forecasting. And then we discuss about neural network model architecture issues, for example, what type of neural network learning architecture is selected for our time series forecasting, and what input size should be applied to a model. In this study an input selection problem is limited to a size selection of the lagged input variables. To solve this problem, we simulate on analyzing and comparing a few neural networks having different model architecture and also use an embedding dimension measure as chaotic time series analysis or nonlinear dynamic analysis to reduce the dimensionality (i.e. the size of time delayed input variables) of the models. Throughout our study, experiments for integration methods of joint time-frequency analysis and neural network techniques are applied to a case study of daily Korean won / U. S dollar exchange returns and finally we suggest an integration framework for future research from our experimental results.

• Journal of IKEEE
• /
• v.22 no.4
• /
• pp.999-1005
• /
• 2018

This paper proposed a search-based high resolution frequency estimation method in power systme. The proposed frequency estimation method adopts a slope-based adaptive search as a base of adaptive estimation structure. The architectural and operational parameters in this adaptive algorithm are changed using the information from context layer analysis of the signals including a localized full-search of spectral peak. The convergence rate of the proposed algorithm becomes much faster than those of other conventional slope-based adaptive algorithms by effectively reducing search range with the application of the localized full-search of spectrum peak. The improvements in accuracy and convergence rate of the proposed algorithm are confirmed through the performance comparison with other representative frequency estimation methods, such as, DFT(discrete Fourier transform) method, ECKF(extended complex Kalman filter), and MV(minimum variable) method.

• 제어로봇시스템학회:학술대회논문집
• /
• 1996.10a
• /
• pp.303-306
• /
• 1996

We propose a robust tuning method of the quadratic criterion based iterative learning control(Q-ILC) algorithm for discrete-time linear batch system. First, we establish the frequency domain representation for batch systems. Next, a robust convergence condition is derived in the frequency domain. Based on this condition, we propose to optimize the weighting matrices such that the upper bound of the robustness measure is minimized. Through numerical simulation, it is shown that the designed learning filter restores robustness under significant model uncertainty.

• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.31A no.10
• /
• pp.39-47
• /
• 1994

In this paper, by modeling the Multilayer-Multiconductor Transmission Line(MMTL) with the characteristic parameters-effective dielectric constant, eigen modal voltages, characteristic impedances at each mode, pulse propagation characteristics of MMTL network are simulated. Transmission line modelling is performed in frequency domain, then time domain resposes are obtained by transforming the frequency domain response using fast Fourier transform.

• 제어로봇시스템학회:학술대회논문집
• /
• 2002.10a
• /
• pp.90.3-90
• /
• 2002

$\textbullet$ Introduction of fuzzy logic controller for dynamic system under irregular disturbance $\textbullet$ Fuzzy rules by displacement information and the frequency characteristics of the system $\textbullet$ Modal analysis for the frequency informations of the system $\textbullet$ Introduction of mode selecting unit(MSU) based on Fast-Fourier transform(FFT) algorithm $\textbullet$ Piezo ceramic as an actuator of flexible structure

• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.32A no.8
• /
• pp.56-63
• /
• 1995

A new method is presented for the synthesis of lossy tapered transmission line having presecribed frequency characteristic in the passband. The theory of lossy case extends lossless cases suggested by Klopfenstein and others, and a special optimization process based on the Fourier transfrom pair and generalized Taylor's procedure is proposed for exact designs of frequency-dependent and distance-dependent lossy tapered line. The process is achieved by control of zero points of lobe-like input reflection coefficient. The validity of the suggested method is confirmed by synthesizing a lossy microstrip transformer and analyzing the simulation results.