• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제16권1호
• /
• pp.350-364
• /
• 2022

Traditionally, in multi-user multi-carrier systems, the neighboring subband will be gapped by one subcarrier, which is set as guard band to reduce multiple access interference (MAI) between neighboring subbands. The empty subcarrier for guard band will degrade the spectral efficiency of the whole system. In order to enhance the spectral efficiency of multi-user filter bank multiple carrier (FBMC) systems, a new subband allocation method is introduced, in which the neighboring subband is gapped by half subcarrier instead of one subcarrier. Meanwhile, in order to implement the proposed resource allocation scheme, an optimized FBMC prototype filter is designed to decrease the inter-subband interference to the neighboring subband. The detailed simulations about the comparison between the proposed spectrum assignment and traditional FBMC are given, as well as the performance in the different interference scenarios. The simulation results show that the combination of the proposed spectrum assignment scheme and the optimized filter has better performance compared to the traditional scheme. The proposed scheme can be used in the system which serves massive users to get higher spectrum efficiency.

• 대한원격탐사학회지
• /
• 제38권4호
• /
• pp.327-341
• /
• 2022

Cloud removal is often required to construct time-series sets of optical images for environmental monitoring. In regression-based cloud removal, the selection of an appropriate regression model and the impact analysis of the input images significantly affect the prediction performance. This study evaluates the potential of Gaussian process (GP) regression for cloud removal and also analyzes the effects of cloud-free optical images and spectral bands on prediction performance. Unlike other machine learning-based regression models, GP regression provides uncertainty information and automatically optimizes hyperparameters. An experiment using Sentinel-2 multi-spectral images was conducted for cloud removal in the two agricultural regions. The prediction performance of GP regression was compared with that of random forest (RF) regression. Various combinations of input images and multi-spectral bands were considered for quantitative evaluations. The experimental results showed that using multi-temporal images with multi-spectral bands as inputs achieved the best prediction accuracy. Highly correlated adjacent multi-spectral bands and temporally correlated multi-temporal images resulted in an improved prediction accuracy. The prediction performance of GP regression was significantly improved in predicting the near-infrared band compared to that of RF regression. Estimating the distribution function of input data in GP regression could reflect the variations in the considered spectral band with a broader range. In particular, GP regression was superior to RF regression for reproducing structural patterns at both sites in terms of structural similarity. In addition, uncertainty information provided by GP regression showed a reasonable similarity to prediction errors for some sub-areas, indicating that uncertainty estimates may be used to measure the prediction result quality. These findings suggest that GP regression could be beneficial for cloud removal and optical image reconstruction. In addition, the impact analysis results of the input images provide guidelines for selecting optimal images for regression-based cloud removal.

• 대한의용생체공학회:의공학회지
• /
• 제29권6호
• /
• pp.477-483
• /
• 2008

The observations of difference and similarity in brain activities involved in processing different languages have fundamental importance in cognitive neuroscience. The purpose of this study was to investigate the difference and similarity in temporal brain activation patterns due to the language difference during visual perception of Korean and English words under priming. Especially, we tried to find the difference in evoked spectral power in gamma-band, which is known to reflect feature binding. The stimulation was visually presented as word pairs belonging to same or different categories so that N400 event-related potential(ERP) was evoked. Average ERP analysis and spectral analysis of gamma-band activity(GBA) were performed on 12 normal Korean subjects. Several ERP components such as P1, N1, N400, and P600 could be identified consistently, and the differences in N1, N400, and P600 were observed. From the spectral analysis, we found that the evoked GBA(eGBA) was significantly larger for English at ${\sim}100$ ms poststimulus. The latency of the eGBA was also considerably delayed for English. Overall, the results on the ERP components and eGBA analyses seem to be commensurate with subjects' familiarity of each language, and the difficulty of perceiving words of each language. The methods of this study can also be applied for clinical purposes considering that the language-related processing can be greatly altered for the patients with neurological or psychiatric diseases.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2010년도 제39회 하계학술대회 초록집
• /
• pp.234-234
• /
• 2010

The PR transitions in asymmetric dot-in-double-quantum-well (DdWELL) photodetector is identified by bias-dependent spectral behaviors. Discrete n-i-n infrared photodetectors were fabricated on a 30-period asymmetric InAs-QD/[InGaAs/GaAs]/AlGaAs DdWELL wafer that was prepared by MBE technique. A 2.0-monolayer (ML) InAs QD ensemble was embedded in upper combined well of InGaAs/GaAs and each stack is separated by a 50-nm AlGaAs barrier. Each pixel has circular aperture of 300 um in diameter, and the mesa cell ($410{\times}410\;{\mu}m^2$) was defined by shallow etching. PR measurements were performed in the spectral range of $3{\sim}13\;{\mu}m$ (~ 100-400 meV) by using a Fourier-transform infrared (FTIR) spectrometer and a low-noise preamplifier. The asymmetric photodetector exhibits unique transition behaviors that near-/far-infrared (NIR/FIR) photoresponse (PR) bands are blue/red shifted by the electric field, contrasted to mid-infrared (MIR) with no dependence. In addition, the MIR-FIR dual-band spectra change into single-band feature by the polarity. A four-level energy band model is proposed for the transition scheme, and the field dependence of FIR bands numerically calculated by a simplified DdWELL structure is in good agreement with that of the PR spectra. The wavelength shift by the field strength and the spectral change by the polarity are discussed on the basis of four-level transition.

• 한국식품과학회지
• /
• 제29권3호
• /
• pp.595-600
• /
• 1997

양파껍질중에 존재하는 항산화물질을 여러 용매로 분획하여 그 항산화효과를 비교하고, butanol fraction의 TLC에 의한 재분획 및 총페놀함량, 수소공여능 및 UV spectral 분석을 행하였다. 메타놀추출물의 항산화 효과는 첨가농도가 증가함에 따라 증가되었다. 메타놀추출물의 용매 분획물의 항산화효과는 buthanol> ethyl acetate> ethyl ether>water fraction의 순으로 나타났다. 이들의 항산화효과는 총페놀함량 및 수소공여능과 밀접한 관계를 보였다. TLC에 의한 butanol fraction의 재분획 결과 Rf치 0.20, 0.33, 0.49, 0.60 및 0.94을 나타내는 형광띠를 나타내었다. Rf치 0.94의 형광 band는 다른 형광 band에 비해 현저히 강한 것으로 보여 주었으며 flavonol의 존재를 나타내는 에서 나타나는 255 nm와 317 nm에서 강한 흡수가 보였다. Spectral analyses 결과 양파껍질 중에 함유되어 있는 주요 항산화성 물질은 quercetin aglycone (3,3',4',5,7-pentahydroxyflavone)인 것으로 확인되었다.

• Journal of Communications and Networks
• /
• 제5권4호
• /
• pp.290-302
• /
• 2003

Ultra wide band (UWB) radio has recently attracted increased attention due to its expected unlicensed operation, and potential to provide very high data rates at relatively short ranges. In this article we briefly describe some main candidate multiple access and modulation schemes for UWB communications, followed with their power spectral density calculation and properties. We also present some illustrative capacity results, and provide a discussion of the impact of network topology on multiple access capacity.

• 천문학회보
• /
• 제38권1호
• /
• pp.62.1-62.1
• /
• 2013

The Cassini/Visual Infrared Mapping Spectrometer (VIMS) observed the sun through the atmosphere of Titan, and provided vertically-resolved 63 spectra from 49 km to 987 km for the 1 - 5 micron range (Bellucci, 2008). Bellucci et al. (2009) analyzed selected spectral ranges where the band absorptions of $CH_4$ and CO are strong by constructing synthetic spectra including $CH_4$ and CO lines, but without including haze absorptions in their synthetic spectra. Kim et al. (2011) and Sim et al. (2013) were able to extract detailed spectral features of fundamental (Dv = 1) and overtone (Dv = 2) bands of the haze from the VIMS spectra by excluding the adjacent influences of strong $CH_4$ absorptions using a radiative transfer program, which includes effects of absorption and emission of lines of these molecules, and absorption and scattering of haze particles. In this presentation, we extend our detailed analyses to other remaining wavelengths in order to provide the spectral characteristics of the Titanian haze for the entire 1 - 5 micron range and to identify any additional haze spectral features and an unidentified feature near 4.3 microns reported by Bellucci et al. (2009).

• 대한조선학회논문집
• /
• 제52권1호
• /
• pp.88-95
• /
• 2015

For the frequency-domain spectral fatigue analysis, the probability density function of stress range needs to be estimated based on the stress spectrum only, which is a frequency domain representation of the response. The probability distribution of the stress range of the narrow-band spectrum is known to follow the Rayleigh distribution, however the PDF of wide-band spectrum is difficult to define with clarity due to the complicated fluctuation pattern of spectrum. In this paper, efforts have been made to figure out the links between the probability density function of stress range to the structural response of wide-band Gaussian random process. An artificial neural network scheme, known as one of the most powerful system identification methods, was used to identify the multivariate functional relationship between the idealized wide-band spectrums and resulting probability density functions. To achieve this, the spectrums were idealized as a superposition of two triangles with arbitrary location, height and width, targeting to comprise wide-band spectrum, and the probability density functions were represented by the linear combination of equally spaced Gaussian basis functions. To train the network under supervision, varieties of different wide-band spectrums were assumed and the converged probability density function of the stress range was derived using the rainflow counting method and all these data sets were fed into the three layer perceptron model. This nonlinear least square problem was solved using Levenberg-Marquardt algorithm with regularization term included. It was proven that the network trained using the given data set could reproduce the probability density function of arbitrary wide-band spectrum of two triangles with great success.

• 한국인터넷방송통신학회논문지
• /
• 제21권5호
• /
• pp.149-154
• /
• 2021

초분광 이미지는 일반 이미지와 달리 전자기 스펙트럼을 파장에 따라 수많은 밴드로 나누어 촬영된 것으로 고용량 고해상도 이미지이다. 일반 이미지보다 정보량이 많아 물체나 물질 탐사에 활용된다. 처리할 초분광 이미지의 정보량을 줄이기 위해 밴드 선택(band selection)기법을 활용한다. 기존 밴드 선택기법들은 통계를 바탕으로 하는 휴리스틱한 기법으로, 시간이 오래 걸리며, 일반성과 보편성이 떨어지는 경우가 많다. 이를 보완하기 위해 본 논문에서는 양자화 개념(Quantization)를 활용하여, 이산 범위(Discrete Range)를 통해 범위별로 대표적인 밴드를 뽑아 밴드 선택에 사용한다. 실험 결과를 통해 제안 기법이 기존 밴드 선택 방식보다 수행 시간이 매우 빠르며 밴드 수를 1/10~1/7로 줄였음에도 원본과 성능 정확도가 유사함을 보였다.

• 전기전자학회논문지
• /
• 제24권4호
• /
• pp.1122-1128
• /
• 2020

대역 확장(Bandwidth Extension)이란 채널 용량 부족 혹은 이동통신 기기에 탑재된 코덱의 특성으로 인해 부호화 및 복호화 과정에서 대역 제한(band limited)되거나 손상된 협대역 신호(NB, Narrow Band)를 복원, 확장하여 광대역 신호(WB, Wide Band)로 전환 시켜주는 것을 의미한다. 대역 확장 연구는 주로 음성 신호 위주로 대역 복제(SBR, Spectral Band Replication), IGF(Intelligent Gap Filling)과 같이 고대역을 주파수 영역으로 변환하여 복잡한 특징 추출 과정을 거쳐 이를 바탕으로 사라지거나 손상된 고대역을 복원한다. 본 논문에서는 딥러닝 모델 중 오토인코더(Autoencoder)를 바탕으로 1차원 합성곱 신경망(CNN, Convolutional Neural Network)들의 잔차 연결을 활용하여 복잡한 사전 전처리 과정 없이 일정한 길이의 시간 영역 신호를 입력시켜 대역 확장 시킨 음향 신호를 출력하는 모델을 제안한다. 또한 음성 영역에 제한되지 않는 음악을 포함한 여러 종류의 음원을 포함하는 데이터셋에 훈련시켜도 손상된 고대역을 복원할 수 있음을 확인하였다.