• ETRI Journal
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• 제38권6호
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• pp.1190-1196
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• 2016

We propose a new bandpass filter (BPF)-based online channel normalization method to dynamically suppress channel distortion when the speech and channel noise components are unknown. In this method, an adaptive modulation frequency filter is used to perform channel normalization, whereas conventional modulation filtering methods apply the same filter form to each utterance. In this paper, we only normalize the two mel frequency cepstral coefficients (C0 and C1) with large dynamic ranges; the computational complexity is thus decreased, and channel normalization accuracy is improved. Additionally, to update the filter weights dynamically, we normalize the learning rates using the dimensional power of each frame. Our speech recognition experiments using the proposed BPF-based blind channel normalization method show that this approach effectively removes channel distortion and results in only a minor decline in accuracy when online channel normalization processing is used instead of batch processing

• IEIE Transactions on Smart Processing and Computing
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• 제1권3호
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• pp.143-151
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• 2012

A new data-driven method for the design of a blind modulation frequency filter that suppresses the slow-varying noise components is proposed. The proposed method is based on the temporal local decorrelation of the feature vector sequence, and is done on an utterance-by-utterance basis. Although the conventional modulation frequency filtering approaches the same form regardless of the task and environment conditions, the proposed method can provide an adaptive modulation frequency filter that outperforms conventional methods for each utterance. In addition, the method ultimately performs channel normalization in a feature domain with applications to log-spectral parameters. The performance was evaluated by speaker-independent isolated-word recognition experiments under additive noise environments. The proposed method achieved outstanding improvement for speech recognition in environments with significant noise and was also effective in a range of feature representations.

• JSTS:Journal of Semiconductor Technology and Science
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• 제13권2호
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• pp.170-183
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• 2013

This paper gives an overview of fractional-N phase-locked loops (PLLs) with practical design perspectives focusing on a ${\Delta}{\Sigma}$ modulation technique and a finite-impulse response (FIR) filtering method. Spur generation and nonlinearity issues in the ${\Delta}{\Sigma}$ fractional-N PLLs are discussed with simulation and hardware results. High-order ${\Delta}{\Sigma}$ modulation with FIR-embedded filtering is considered for low noise frequency generation. Also, various architectures of finite-modulo fractional-N PLLs are reviewed for alternative low cost design, and the FIR filtering technique is shown to be useful for spur reduction in the finite-modulo fractional-N PLL design.

• ETRI Journal
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• 제43권6호
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• pp.966-977
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• 2021

Filterbank multicarrier with offset quadrature amplitude modulation (FBMC-OQAM) is an attractive alternative to the orthogonal frequency division multiplexing (OFDM) modulation technique. In comparison with OFDM, the FBMC-OQAM signal has better spectral confinement and higher spectral efficiency and tolerance to synchronization errors, primarily due to per-subcarrier filtering using a frequency-time localized prototype filter. However, the filtering process introduces intrinsic interference among the symbols and complicates channel estimation (CE). An efficient way to improve the CE in FBMC-OQAM is using a technique known as windowed frequency domain averaging (FDA); however, it requires a priori knowledge of the window length parameter which is set based on the channel's frequency selectivity (FS). As the channel's FS is not fixed and not a priori known, we propose a k-nearest neighbor-based machine learning algorithm to classify the FS and decide on the FDA's window length. A comparative theoretical analysis of the mean-squared error (MSE) is performed to prove the proposed CE scheme's effectiveness, validated through extensive simulations. The adaptive CE scheme is shown to yield a reduction in CE-MSE and improved bit error rates compared with the popular preamble-based CE schemes for FBMC-OQAM, without a priori knowledge of channel's frequency selectivity.

• 한국통신학회논문지
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• 제17권9호
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• pp.1029-1039
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• 1992

본 논문은 한글인식 방법중 주파수 변환영역에서 행하는 필터링의 방법을 제시한 것이다. 한글 문자패턴을 2차원 변조처리하여 공간위치에 의존적인 한글자소의 위상문자적 특징을 주파수 영역으로 사상하였고, 이때 변조 주파수를 정규화함으로서 주파수 영역에서 문자의 크기를 정규화 한다. 또한 한글의 각 자소를 발생위치에 따라 분류하여 표준패턴으로 설정하고, 설정된 각 자소의 표준패턴을 자소필터로 사용하여 주파수 영역으로 사상된 문자패턴을 필터링하였다. 한글자소의 분별 파라미터로는 정규화된 상호상관함수와 필터링 결과로 부터 유도된 코히어런스 함수를 산출하여 분별기준을 설정하였으며, 그 결과로서 문자크기의 변화, 자소의 융착, 제한적인 자획의 유실이나 잡음의 혼입등의 요인이 발생하였음 경우에도 한글자소의 분별이 가능하였고 또한 표준패턴을 설정함에 따라 숫자, 영문자등의 분별에도 적용할 수 있었다.

• 전자공학회논문지 IE
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• 제45권1호
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• pp.24-30
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• 2008

DMT 변조 방식은 VDSL에 적용된 다중 반송파 변조 방식이다. DMT 변조 방식의 문제는 송수신 반송파 주파수들 사이의 주파수 오프셋(Offset)에 민감하다는 것이다. 이러한 주파수 오프셋은 DMT 심볼에서 반송파간 간섭을 야기한다. 본 논문에서는 칼만(Kalman) 필터링을 이용하여 ICI를 감소하는 방법을 제안한다. 제안한 방식은 다른 방식과의 성능과 대역폭 그리고 계산상 복잡도를 비교한다. 시뮬레이션 결과는 제안한 방식의 성능이 주파수 오프셋이 높은 경우와 높은 차수의 변조 방식에 대해서 다른 방식에 대해서 칼만 필터링을 이용한 방식이 더 좋은 성능을 나타내었다.

• 한국해양공학회지
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• 제2권2호
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• pp.37-45
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• 1988

A dynamically positioned vessel must be capable of maintaining a specified position and direction by controlling the thruster devices. The motions of a vessel are often assuned to tne sum of low frequency(LF)motions and high frequency(HF)motions. The former is mainly due to wind, current and second order wave forces, while the latter is mainly due to first order wave forces. In order to avoid the high frequency thruser modulation, the control system must include filters to estimate the low frequency motions from the measured motion signals, This paper presents a control system based on Kalman filtering technique and optimal control tyeory. Using the combined kalmam filter, LF motion estimates and HF ones are achieved from the motion measurement of the vessel. The estimated low frequency motions are used as inputs to the dynamic positioning system. The thruster modulation is minimized using the optimal control theory; Linear Quadratic Gaussian(LQG)controller. The performances of the Kalman filter and the dynamic positioned vessel are investigated by computer simulation.

• Journal of the Optical Society of Korea
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• 제17권1호
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• pp.63-67
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• 2013

We perform an optical vestigial sideband (VSB) filtering using a pair of Fabry-Perot (FP) filters. The transmittance curve of each FP filter is made to have sharp skirts using an offset between input and output coupling fibers. Moreover, the accurate periodicity of FP filters in the optical frequency domain enables the simultaneous VSB filtering of a large number of optical channels. With this VSB filtering technique, we transmit 12.5-GHz spaced $64{\times}12.4-Gb/s$ wavelength-division-multiplexing channels over a single-mode fiber up to 150 km without any dispersion compensations. When the channel spacing is reduced to 10 GHz, we achieve the spectral efficiency of 1 bit/s/Hz in conventional optical intensity modulation systems up to 125 km.

• Journal of Power Electronics
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• 제16권1호
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• pp.153-162
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• 2016

Given their structural arrangement, photovoltaic (PV) modules exhibit parasitic capacitance, which creates a path for high-frequency current during zero-state switching of the converter in transformerless systems. This current has to be limited to ensure safety and electromagnetic compatibility. Many solutions that can minimize or completely avoid this phenomenon, are available. However, most of these solutions are patented because they rely on specific and often complex converter topologies. This study aims to solve this problem by introducing a solution based on a classic converter topology with an appropriate modulation technique and passive filtering. A 5.5 kW single-phase residential PV system that consists of DC-DC boost stage and DC-AC H-bridge converter is considered. Control schemes for both converter stages are presented. An overview of existing modulation techniques for H-bridge converter is provided, and a modification of hybrid modulation is proposed. A system prototype is built for the experimental verification. As shown in the study, with simple filtering and proper selection of switching states, achieving low leakage current level is possible while maintaining high converter efficiency and required energy quality.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2000년도 제15차 학술회의논문집
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• pp.543-543
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• 2000

A new method for HRV(heart rate variability) detection from the R-wave signal, based on the IPFM(integral pulse frequency modulation) model and its similarity to pulse position modulation, is presented. The proposed method exert lowpass filtering with a Kaiser window. In this paper, The proposed method presents a powerful, but simple, tool for investigation of HRV. It also guarantees real-time behavior. simplicity in design, and phase linearity. Even without the basic assumption of IPFM model. the new algorithm can still be used on-line and with higher performance. It is thoroughly proved that lowpass filtering is an ideal method for PSD(Power Spectrum Density) analysis of HRV.