• Aerospace Engineering and Technology
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• v.8 no.1
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• pp.58-65
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• 2009

The paper identifies noise characteristics of a nonliner image sensor model which reflects a saturation effect of each detector pixel and extends the result to estimate an image SNR (Signla-to-Noise Ratio) distribution over all the pixels in a detector. In particular, nonlinearity of a pixel is studied from two perspectives of including asymmetry of a noise PDF (Probability Distribution Function) and enhancing a pixel SNR value, in comparison to a linear model. It is noted that the proposed image SNR distribution function is useful to effectively select new optimal operation parameter values: an integration time and an pixel-summing number, even after a launch campaign, assuming sensor gain degradation in orbit or inevitable modification of some operation parameter values due to space contingency.

• Aerospace Engineering and Technology
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• v.8 no.2
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• pp.160-169
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• 2009

In the paper, the Image SNR(Signal-to-Noise) distribution proposed in [1] is reviewed from the three points of views: verification, variation, and application of the distribution. First, the proposed Image SNR distribution is verified through the noise-based simulation over a 2D image detector. Second, its variation over the linear/nonlinear gains shows that the noise-effect itself cannot explain every reason for the degraded Image SNR distribution. Third, through the application to optimal selection of the operation parameters, the usefulness of the proposed distribution is clarified.

• 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.

• 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 Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.5
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• pp.430-437
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• 2016

In general, noise measurement results show larger random ripple than those of the network analyzer. The reason for the lager random ripple of the noise measurements is considered that the general noise measurements uses absolute measured noise powers, while the network analyzer measures using a ratio of the measured powers. In this paper, a novel measurement method of noise correlation matrix using relative noise ratios is proposed. Proposed method measures the five noise powers of DUT for the five input impedance variations and the four relative noise ratios are formed using the five measured noise powers. The four noise ratios are used to compute the noise correlation matrix and noise parameters. The resulting noise parameters for a 0.5 dB attenuator show good agreements with theoretical values calculated by S-parameters. Also, the noise parameters of an active DUT with a noise figure of less than 1 dB are measured and the measured results show a small random ripple as expected and their values are physically acceptable. In conclusion, the proposed method can be applied to the noise parameter measurements for DUT with a noise figure below 1 dB.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.1
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• pp.54-62
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• 1999

In this paper, we investigated the signal-to-noise ratio improvement in a differential detector, which is a function of the optical noise coupling ratio and the differential gain ratio. A differential detector consists of two photodiodes and a differential amplifier. The differential detector reduced the noise component and improved the signal-to-noise ratio by about 20 dB when the differential gain ratio equals to the optical noise coupling ratio. The differential detector is very effective in removing the environmental optical noise or interference from an adjacent optical channel. This method is also effective when the noise wavelength is similar to the signal.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.07a
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• pp.394-395
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• 2010

본 논문은 최소 평균 제곱 오차(minimum mean-square error: MMSE)에 기반한 비국소적 (nonlocal) 평균 영상 잡음 제거기법을 제안한다. 제안하는 기법에서는 기존의 비국소적 평균 기법에 추정 이론을 적용하여 잡음 제거에 사용되는 이웃 블록 또한 잡음을 포함하는 일반적인 경우로 확장하여 이웃 블록에 인가되는 가중치를 적응적으로 조절한다. 컴퓨터 모의실험을 통해 제안하는 알고리듬이 기존의 비국소적 기법에 비해 잡음 제거 성능이 향상됨을 확인한다.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2000.11a
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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.

• The Journal of the Acoustical Society of Korea
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• v.28 no.1
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• pp.77-83
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• 2009

This paper proposes a new noise-biased compensation of minimum statistics(MS) method using a nonlinear function and a priori speech absence probability(SAP) for speech enhancement in non-stationary noisy environments. The minimum statistics(MS) method is well known technique for noise power estimation in non-stationary noisy environments. It tends to bias the noise estimate below that of true noise level. The proposed method is combined with an adaptive parameter based on a sigmoid function and a priori speech absence probability (SAP) for biased compensation. Specifically. we apply the adaptive parameter according to the a posteriori SNR. In addition, when the a priori SAP equals unity, the adaptive biased compensation factor separately increases ${\delta}_{max}$ each frequency bin, and vice versa. We evaluate the estimation of noise power capability in highly non-stationary and various noise environments, the improvement in the segmental signal-to-noise ratio (SNR), and the Itakura-Saito Distortion Measure (ISDM) integrated into a spectral subtraction (SS). The results shows that our proposed method is superior to the conventional MS approach.

• The Journal of the Acoustical Society of Korea
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• v.13 no.2
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• pp.76-85
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• 1994

A speech enhancement algorithm which attenuates nonstationary colored noise is presented In this paper. The algorithm consists of a stationary Kalman filter and the simple speech/nonspeech detector. While the conventional enhancement systems are focused on a stationary and/or white background noise, this study Is focused on the mort realistic nonstationary and nonwhite noise. An AR model-based vector Kalman filter is used as a noise suppression system and a short-time energy threshold logic is used as a speech/nonspeech classifier. For Kalman filtering. noise coefficients are estimated in the nonspeech frame, and speech coefficients are estimated by applying the EM iteration algorithm. Simulation results using the car noise are presented based on the signal-to-noise ratio and informal listening tests. According to the experimental results, background noises in the nonspeech frames are eliminated almost completely, while some distortions are noticed in the speech frames. The distortion becomes severer as the SNR is reduced to 0dB and -5dB. Intelligibility, however, is not degraded significantly.