• Title, Summary, Keyword: 신호대 잡음비

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Performance Analysis of DS/CDMA System in Multipath Rayleigh fading and Impulsive Noise Environments (다중경로 레일리 패이딩과 임펄스 잡음 환경에서 DS/CDMA 시스템의 성능 분석)

  • 강희곡;조성준;조성언
    • Proceedings of the Korea Electromagnetic Engineering Society Conference
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    • pp.292-296
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    • 2000
  • 본 논문에서는 임펄스 잡음과 다중경로 레일리 페이딩이 함께 존재하는 최악의 채널 환경에서 비동기 DS/CDMA BPSK 시스템의 오율식을 유도하고 수치계산 하여 BER 성능을 분석하였다. 그 결과, 비교적 낮은 신호 대 잡음 전력비 영역에서 시스템의 BER 성능은 임펄스 잡음의 영향으로 크게 열화되지만 페이딩의 영향은 거의 없다. 그러나, 임펄스 잡음의 영향이 작아지는 높은 신호 대 잡음 전력비에서는 페이딩에 의해서 BER 성능이 결정된다. 다중사용자의 간섭도 낮은 신호 대 잡음 전력비 영역에서는 BER 성능에 거의 영향을 미치지 못하지만 높은 신호 대 잡음 전력비 영역에서는 BER 성능을 좌우한다 그러나, 실제 이동통신 시스템에서는 비교적 낮은 신호 전력을 사용하므로, 임펄스 환경에서 페이딩을 경감하기 위한 방법이나, 다중사용자 간섭을 줄이기 위한 기법을 적용하더라도 성능 개선이 거의 되지 않는다.

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Preprocessing Technique for Improvement of Speech Recognition in a Car (차량에서의 음성인식율 향상을 위한 전처리 기법)

  • Kim, Hyun-Tae;Park, Jang-Sik
    • The Journal of the Korea Contents Association
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    • v.9 no.1
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    • pp.139-146
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    • 2009
  • This paper addresses a modified spectral subtraction schemes which is suitable to speech recognition under low signal-to-noise ratio (SNR) noisy environment such as the automatic speech recognition (ASR) system in car. The conventional spectral subtraction schemes rely on the SNR such that attenuation is imposed on that part of the spectrum that appears to have low SNR, and accentuation is made on that part of high SNR. However, such postulation is adequate for high SNR environment, it is grossly inadequate for low SNR scenarios such as that of car environment. Proposed methods focused specifically to low SNR noisy environment by using weighting function for enhancing speech dominant region in speech spectrum. Experimental results by using voice commands for car show the superior performance of the proposed method over conventional methods.

Signal-to-noise Ratio in Time- and Frequency-domain Photoacoustic Measurements by Different Frequency Filtering (주파수 필터링 함수에 따른 시간 및 주파수 영역 광음향 측정에 대한 신호 대 잡음비 분석)

  • Kang, DongYel
    • Korean Journal of Optics and Photonics
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    • v.30 no.2
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    • pp.48-58
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    • 2019
  • We investigate the signal-to-noise ratios (SNRs) of time-domain (i.e. pulsed illumination) and frequency-domain (i.e. chirped illumination) photoacoustic signals measured by a spherically focused ultrasound transducer for spherical absorbers. The simulation results show that the time-domain photoacoustic SNR is higher than that of frequency-domain photoacoustic signals, as reported in the previous literature. We understand the reason for this SNR gap between the two measurement modes by analyzing photoacoustic-signal spectra, considering the incident beam energy controlled by the maximum permissible exposure. As the result of this approach, we find that filtering off the DC term in the chirped signal's spectrum improves frequency-domain photoacoustic SNRs by up to approximately 5 dB. In particular, it is observed that photoacoustic SNRs are highly sensitive to an upper-frequency value of frequency filtering functions, and the optimal upper-frequency values maximizing the SNR are different in time- and frequency-domain photoacoustic measurements.

SNR and ADC Value Change before and after the injection of contrast medium during DWI test on metastatic spinal cancer patients (전이성 척추암 환자의 확산강조영상 검사 시 조영제 주입 전.후 ADC값의 변화에 대한 고찰)

  • Kim, Eng-Chan;Kim, Ki-Hong;Park, Cheol-Soo;Lee, Sun-Yeob;Yoo, Heung-Joon;Cho, Jae-Hwan;Jang, Hyun-Cheol;Kim, Bo-Hui;Han, Man-Seok
    • Journal of the Korean Society of Radiology
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    • v.5 no.1
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    • pp.37-49
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    • 2011
  • To examine the possible changes in the SNRs, CNRs, and ADC values for lumbar spines with metastasis based on the DW images before and after contrast agent injection taken from metastatic spinal cancer patients using a 1.5 T MR machine. The quantitative analysis revealed that in case of spinal cancer subjects, both SNRs and CNRs at all of those assessed locations significantly increased on the DWI after contrast agent injection compared to before, while on the ADC map images, SNRs significantly decreased. On the other hand, significantly decreased ADC values at all the assessed locations were found on the ADC map images. With reference to the normal group, significantly increased SNRs were found at all of the assessed locations on the DWI image after injection compared to before, while significantly decreased SNRs were found on the ADC map images. Also, significantly decreased ADC values at all the assessed locations were found on the ADC map images. For the qualitative analysis, after contrast agent injection, significantly increased signal intensities were found at the locations with spinal cancer on the DWI. In contrast, significantly decreased signal intensities were found on the ADC map images. The implication from the results showing that SNR and CNR significantly increased while ADC value significantly decreased at, above, and below the location of metastatic spinal cancer on DWI after contrast agent injection is that DWI obtained after contrast agent injection can be made available for wider application to vertebral disorders.

Noise Performance Design of CMOS Preamplifier for the Active Semiconductor Neural Probe (신경신호기록용 능동형 반도체미세전극을 위한 CMOS 전치증폭기의 잡음특성 설계방법)

  • 김경환;김성준
    • Journal of Biomedical Engineering Research
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    • v.21 no.5
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    • pp.477-485
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    • 2000
  • 본 논문에서는 신경신호기록을 위한 반도체 미세전극용 전치증폭기의 잡음특성을 설계하기 위한 체계적인 방법을 제시한다. 세포외기록(extracellular recording)에 의하여 측정된 신경신호와 전형적인 CMOS소자의 저주파 잡음특성을 함계 고려하여 전체 신호대잡음비를 계산하였다. 2단 CMOS 차동증폭기에 대한 해석과 함께 신호대잡음비에 중요한 영향을 끼치는 요소들에 대하여 설명하였다. 출력잡음전력에 대한 해석적인식을 유도하였으며 이로부터 회로설계자가 조절할 수 있는 주파수응답과 소자 파라미터들을 결정하였다. 입력소자의 크기와 트랜스컨덕턴스의 비가 최적영역으로부터 약간 벗어날 경우에 신호대잡음비가 크게 저하됨을 보였다. 이와 함께 만족스런 잡음특성을 위한 증폭이의 설계 변수 값들도 제시하였다.

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An alternative procedure for parameter design using desirability function in combined array (통합배열에서 기대함수를 이용한 파라미터설계 대체방안)

  • Kwon, Yong Man
    • Journal of the Korean Data and Information Science Society
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    • v.27 no.5
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    • pp.1263-1272
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    • 2016
  • Product array approach which is used in the Taguchi parameter design has a number of advantages by considering the noise factor. However, a disadvantage of this method is that it requires an excessively large number of experiments. So combined array approach have been proposed to reduce the number of experiments. Taguchi has used the signal-to-noise ratio to find the optimum conditions in the Taguchi parameter design. In analyzing the data from the parameter design various problems tends occur by using an SN. In this paper, we propose an alternative solution for reducing the number of experiments without depending on the signal-to-noise ratio to overcome the shortcomings of the parameter design. Two examples illustrate this procedure in the two different experimental design (product array, combined array) approaches.

Study on Low Temperature Radiofrequencey Coils for the Signal-to-Noise Ratio Improvement of Nuclear Magnetic Resonance (핵자기공명 신호 향상을 위한 저온 고주파코일 연구)

  • Kim, Song-Hee;Lee, Dong-Hoon
    • The Journal of Natural Sciences
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    • v.13 no.1
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    • pp.15-23
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    • 2003
  • 본 연구에서는 코일의 온도를 액체질소 온도 정도의 저온으로 냉각시켜 핵자기공명 신호 및 영상의 신호대잡음비를 향상시키는데 그 목적을 두었다. 핵자기공명 신호의 신호대잡음비에 대한 이론적인 분석을 토대로 다양한 형태의 고주파코일을 제작했고, 저온의 표면고주파코일로 획득된 신호를 상온의 일반 구리코일로 획득된 신호와 비교하였다. 본 연구에서 제작된 저온코일의 경우, 상온코일에 비해서 신호대잡음비의 향상을 얻을 수 있었다. 이러한 신호대잡음비의 향상을 통하여 핵자기공명영상 시간을 단축할 수 있으며, 이를 통한 진단의 신뢰도 향상에 기여할 수 있을 것으로 사료된다.

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The Effect of Advanced Modeling Iterative Reconstruction(ADMIRE) on the Quality of CT Images : Non-contrast CT in Chest (고급 모델링 반복 재구성법(ADMIRE)이 CT 영상의 화질에 미 치는 영향: 흉부 비조영 CT에서)

  • Lee, SangHeon;Lee, HyoYeong
    • Journal of the Korean Society of Radiology
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    • v.13 no.2
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    • pp.159-168
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    • 2019
  • We examined the effect of Siemens ADMIRE (Advanced Modeled Iterative Reconstruction) on image quality by measuring changes in HU, noise, and SNR of background air, fat, muscle, and background signals on a chest CT scan. Experimental results show that as the ADMIRE Strength increases, the noise decreases and the signal increases, consequently the signal-to-noise ratio increases. ADMIRE can reduce noise by 28 ~ 61% compared to FBP, which is a conventional image reconstruction algorithm, and improves SNR by 16 ~ 100%.

The quantitative analysis of Diffusion Weighted Imaging in Breast MRI (유방 MRI 검사에서 확산강조영상의 정량적 분석)

  • Cho, Jae-Hwan;Kim, Hyeon-Ju;Hong, Yin-Sik;Lee, Hae-Kag
    • Journal of the Korean Society of Radiology
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    • v.5 no.3
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    • pp.149-154
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    • 2011
  • The purpose of this study was to examine the usefulness of diffusion weighted images in breast MRI by performing a quantitative comparative analysis in patients diagnosed with DCIS. On a 3.0T MR scanner, diffusion weighted images and ADC map images were obtained from 20 patients histologically diagnosed with ductal carcinoma in situ (DCIS). The findings from the quantitative image analysis are the following: The diffusion weighted images showed higher SNR and CNR at the lesion area. In addition, the ADC values were lower at the lesion area.