• Korean Journal of Remote Sensing
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• v.22 no.4
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• pp.275-284
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• 2006

The noise sources of a Hyperion image are mainly due to the atmospheric effects, the sensor's instrumental errors, and A/D conversion. Though uncalibrated, overlapping, and all deep water absorption bands generally are removed, there still exist noisy bands. The visual inspection for selecting clean and stable processing bands is a simple practice, but is a manual, inefficient, and subjective process. In this paper, we propose that the extrema ratio be used for noise estimation and unsupervised band selection. The extrema ratio was compared with existing SNR and entropy measures. First, Gaussian, salt and pepper, and Speckle noises were added to ALI (Advanced Land Imager) images with relatively low noises, and the relation of noise level and those measures was explored. Second, the unsupervised band selection was performed through the EM (Expectation-Maximization) algorithm of the measures which were extracted from a Hyperion images. The Hyperion data were classified into 5 categories according to the image quality by visual inspection, and used as the reference data. The experimental result showed that the extrema ratio could be used effectively for band selection of Hyperion images.

• International journal of advanced smart convergence
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• v.1 no.1
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• pp.48-51
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• 2012

The conventional method for filtering force plate data, low-pass filtering, does not always give accurate results when applied to force data from a custom-made, instrumented treadmill. Therefore, this study compares low-pass filtered data to the same data passed through a wavelet filter. We collected data with the treadmill running. However these include motor noise with ground reaction force at two force plates. We found that he proposed wavelet method eliminated motor noise to result in more accurate force plate data than the conventional low-pass filter, particularly at high speed motor operation. In this study we suggested the convolution wavelet (CNW) which was compared to that of a low-pass filter. The CNW showed better performance as compared to band-pass filtering particularly for low signal-to-noise ratios, and a lower computational load.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.385-390
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• 2006

This paper examines the sampling and jitter specifications and considerations for Global Navigation Satellite Systems (GNSS) software receivers. Software radio (SWR) technologies are being used in the implementation of communication receivers in general and GNSS receivers in particular. With the advent of new GPS signals, and a range of new Galileo and GLONASS signals soon becoming available, GNSS is an application where SWR and software-defined radio (SDR) are likely to have an impact. The sampling process is critical for SWR receivers, where it occurs as close to the antenna as possible. One way to achieve this is by BandPass Sampling (BPS), which is an undersampling technique that exploits aliasing to perform downconversion. BPS enables removal of the IF stage in the radio receiver. The sampling frequency is a very important factor since it influences both receiver performance and implementation efficiency. However, the design of BPS can result in degradation of Signal-to-Noise Ratio (SNR) due to the out-of-band noise being aliased. Important to the specification of both the ADC and its clocking Phase- Locked Loop (PLL) is jitter. Contributing to the system jitter are the aperture jitter of the sample-and-hold switch at the input of ADC and the sampling-clock jitter. Aperture jitter effects have usually been modeled as additive noise, based on a sinusoidal input signal, and limits the achievable Signal-to-Noise Ratio (SNR). Jitter in the sampled signal has several sources: phase noise in the Voltage-Controlled Oscillator (VCO) within the sampling PLL, jitter introduced by variations in the period of the frequency divider used in the sampling PLL and cross-talk from the lock line running parallel to signal lines. Jitter in the sampling process directly acts to degrade the noise floor and selectivity of receiver. Choosing an appropriate VCO for a SWR system is not as simple as finding one with right oscillator frequency. Similarly, it is important to specify the right jitter performance for the ADC. In this paper, the allowable sampling frequencies are calculated and analyzed for the multiple frequency BPS software radio GNSS receivers. The SNR degradation due to jitter in a BPSK system is calculated and required jitter standard deviation allowable for each GNSS band of interest is evaluated. Furthermore, in this paper we have investigated the sources of jitter and a basic jitter budget is calculated that could assist in the design of multiple frequency SWR GNSS receivers. We examine different ADCs and PLLs available in the market and compare known performance with the calculated budget. The results obtained are therefore directly applicable to SWR GNSS receiver design.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.11
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• pp.1645-1654
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• 1993

Unlike a noise removal recursive temporal filter, this paper presents a temporal filter which improves visual quality and data compression efficiency. In general, for the temporal band-limitation, temporal aliasing should be considered. Since most of a video signal has temporally aliased components, it is desirable to consider them. From a signal processing point of view, it is impossible to realize the filtering not afeced by the aliasings. However, in this paper, efficient filtering with de-aliasing characteristics is proposed. Considering the location of a video signal, temporal filtering can be accomplished by the spatial filtering along the motion vector trajectory (Motion Adaptive Spatial Filter). This filtered result dose not include the aliasings. Besides the efficient band-limitation, temporal noise is also reduced. For the evaluation of the MASF, its realization and filtering characteristics will be discussed in ditail.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.10
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• pp.80-88
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• 1997

This paper describes a design of a Wavelet Adaptive Filter(WAF) for the removal of the baseline wandering and the minimization of the signal distortion using by wavelet transform and adaptive filter in the ECG signal. WAF consists of two parts. The first part is wavelet transform that decomposes the ECG signal into seven frequency bands using Vaidyanathan and Hoang wavelet. The second part is adaptive filter that uses the signal of seventh low frequency band among the wavelet transformed signals as primary input and a unit impulse sequence as reference input. For the evaluation of the performance of WAF, we used several baseline wandering elimination filters such as commerical standard filter with cutoff frequency of 0.5Hz and general adaptive filter. We made use of MIT/BIH database and real patient data for the evaluation. In conclusion, WAF showed a lower ST segement distortion than standard filter and adaptive filter and has a higher eliminated noise power than standard filter and adaptive filter.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.5
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• pp.999-1003
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• 1992

Because of low noise and small size with huge capacity, a centrifugal fan is widely used for ventilation, air-conditioner and so on, which are very near to human life. Because of the complexity of its vibration and noise generation mechanics, most of researches on them are based on experimental methods. This study is to characterize the centrifugal fan noise and vibration. It is considered that noise is composed of the structural vibration noise and the air flow induced aerodynamic noise. To decouple the structural vibration noise the centrifugal fan is masked with an adhesive tape, such that air blowing is prohibited thus only the structural vibration noise is extracted. The noise level and characteristics in the frequency domain are verified and compared with those of total mixed one. This study shows some significant results that the structural vibration noise has relatively narrow band power spectrum compared with the total mixed one and has a strong periodicity. The sound level is lowered about 5dB by the removal of air flow with the masked fan for an air-conditioner used in this study.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.66 no.4
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• pp.200-205
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• 2017

In this paper, we propose a technique to determine the normal and arc of an alternating current using a mixed filter composed of an average filter and a band-pass filter and a frequency analysis. The proposed method uses the moving average filter of the FIR filter structure for noise removal and the band-pass filter of the IIR filter structure for detecting only specific frequency components after normalizing the measured current signal based on the maximum value. After performing Fast Fourier Transform (FFT) using the band-pass filtered signal, the total energy is calculated using the magnitude component of the frequency, and the arc is detected using the magnitude of the calculated energy. In order to show the validity of the proposed method, we experimented with various data and found that arc and steady state can be easily discriminated by calculating spectral energy. Therefore, it is considered that the proposed method can be applied to arc diagnosis of low voltage electric wire.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.8
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• pp.1090-1098
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• 2018

Many short range weather radars with the low elevation search capability are needed for analysis and prediction of unusual weather changes or rainfall phenomena which occurs regionally. However, due to the characteristics of low elevation electromagnetic wave beam, it is highly probable that the received weather signals of these radars are seriously contaminated by the ground clutter. Therefore, the filter removing low Doppler frequency band is generally used to mitigate this problem. However, the phase noise in a radar system may limit the removal of the strong clutter and this may cause serious problems in estimating weather parameters because of the remaining clutter. Therefore, in this paper, the characteristics of phase noise in a radar system are investigated and the effects of the system phase noise are analyzed in the improvement of signal to clutter ratio for the strong clutter environment such as a short and low-elevated weather radar.

• JSTS:Journal of Semiconductor Technology and Science
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• v.16 no.6
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• pp.825-831
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• 2016

In this paper, a transimpedance amplifier based on a new DC offset cancellation (DCOC) method is proposed for WCDMA/LTE applications. The proposed method applies a sample and hold mechanism to the conventional DCOC method with a DC feedback loop. It prevents the removal of information around the DC, so it avoids signal-to-noise ratio degradation. It also reduces area and power consumption. It was designed in a $0.13{\mu}m$ deep n-well CMOS technology and drew a maximum current of 1.58 mA from a 1.2 V supply voltage. It showed a transimpedance gain of $80dB{\Omega}$, an input-referred noise current lower than 0.9 pA/${\surd}$Hz, an out-of-band input-referred 3rd-order intercept point more than 9.5 dBm, and an output DC offset lower than 10 mV. Its area is $0.46mm{\times}0.48mm$.

• Proceedings of the KSRS Conference
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• 2008.03a
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• pp.219-223
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• 2008

초분광 영상은 기존의 다중분광 영상보다 많은 파장대의 영상을 취득하기 때문에 다양한 분야의 연구에 이용되고 있다. 하지만 밴드별로 취득하는 파장대가 짧고 밴드수가 많아, 밴드간의 높은 상관관계 및 노이즈 밴드가 존재한다. 이로 인해 기존에 알려진 분석기법의 적용결과가 제대로 도출되지 않는다. 따라서 초분광 영상을 이용할 경우, 노이즈가 많이 포함된 밴드를 제거한 후 영상분석을 하는 것이 보다 효율적이다. 본 연구에서는 초분광 영상(Hyperspectral Image)의 전처리 과정 중 노이즈 밴드 제거에 초점을 맞추었으며, 이를 위해 프랙탈 차원을 이용하였다. 프랙탈 차원 측정방법 중 삼각기둥 표면적 기법을 이용하였다. 프랙탈 차원을 측정하고, Continuum Removal 기법을 이용하여 경향을 살펴보았다. 경험적으로 구한 임계값을 통해 상대적으로 정보량이 적은 밴드를 노이즈 밴드로 판단하여 제거하였다. 실험 영상으로는 EO-1 위성에서 취득되는 Hyperion 초분광 영상을 사용하였다. 실험 결과 프랙탈 분석을 통해 Hyperion 초분광 영상의 노이즈 밴드를 자동으로 추출하여 제거할 수 있음을 확인하였다.