• 대한전자공학회논문지SP
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• 제45권4호
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• pp.100-106
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• 2008

본 논문에서는 다양한 잡음 환경에서 음성의 통계적 모델에 기반한 음성 검출기의 성능향상을 위해 PSFM (Power Spectral Flatness Measure)을 이용하여 실시간으로 변별적 가중치 학습 (Discriminative Weight Training) 기반의 최적화된 우도비 테스트 (Likelihood Ratio Test, LRT)를 제안한다. 먼저, 기존의 통계모델기반의 음성 검출기를 분석하고, 이를 기반으로 MCE (Minimum Classification Error)방법을 도입하여 도출한 각 주파수 채널별 가중치를 PSFM 값에 기반하여 실시간 매 프레임마다 다른 가중치를 적용한 우도비 기반의 음성 검출 결정법을 제시한다. 제안된 알고리즘은 다양한 잡음 환경에서 기존에 제시된 음성 검출기와 비교하였으며, 우수한 성능을 보인다.

• 대한원격탐사학회지
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• 제33권2호
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• pp.159-169
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• 2017

위성용 전자광학탑재체는 제한된 소모전력 및 우주방사선과 같은 사용 환경에 의해 설계부터 특별한 요구사항을 가지고 있으며, 획득 영상의 품질은 주로 GSD (Ground Sampled Distance), 신호대잡음비(SNR, Signal to Noise Ratio), MTF (Modulation Transfer Function)에 따라 좌우된다. 영상센서의 출력신호에 포함된 잡음 감소를 통한 신호대잡음비 개선을 위하여, 센서에 추가된 프리픽셀(Pre-pixel) 및 다크픽셀(Dark-pixel)을 사용하여 CDS (Corrective Double Sampling) 방식을 통해 영상센서의 잡음 성분을 포함한 오프셋 신호(Offset Signal)를 제거하는 아날로그 신호처리(ASP, Analog Signal Processor) 방법을 제안한다. 또한 센서 제어시스템에서는 영상의 불균일성 처리를 위해 제어시스템의 출력 포트별 게인(Gain), 오프셋, 및 센서의 화소별 특성을 반영한 다양한 방식에 의한 보정 방법이 적용된다. 본 논문에서는 이상 설명한 여러 가지 잡음 개선방법을 시스템 설계 및 운영에 적용하여 위성탑재용 전자광학카메라의 신호대잡음비 향상 방법을 제안하고, 실험을 통해 검증한다.

• Nuclear Engineering and Technology
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• 제54권9호
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• pp.3380-3389
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• 2022

We evaluated the performance of an improved hybrid median filter (IHMF) applied to X-ray computed tomography (CT) images obtained using a high-resolution photon-counting cadmium zinc telluride (CZT) detector. To study how the proposed approach improves the image quality, we measured the noise levels and the overall CT-image quality. We established a CZT imaging system with a detector length of 5.12 cm and thickness of 0.3 cm and acquired phantom images. To evaluate the efficacy of the proposed filter, we first modeled two conventional median filters. Subsequently, we were able to achieve a normalized noise power spectrum result of ~10^-8 mm², and furthermore, the proposed method improved the contrast-to-noise ratio by a factor of ~1.51 and the coefficient of variation by 1.55 relative to the counterpart values of the no-filter image. In addition, the IHMF exhibited the best performance among the three filters considered as regards the peak signal-to-noise ratio and no-reference-based image-quality evaluation parameters. Thus, our results demonstrate that the IHMF approach provides a superior image performance over conventional median filtering methods when applied to actual CZT X-ray CT images.

• Nuclear Engineering and Technology
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• 제44권8호
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• pp.977-984
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• 2012

The cross-correlation technique has been widely used for leakage detection of buried pipes, and this technique can be successfully applied when the leakage signal has a high signal-to-noise ratio. In the case of a power plant, the measured leakage signals obtained from the sensors may contain background noise and mechanical noise generated by adjacent machinery. In such a case, the conventional method using the cross-correlation function may fail to estimate the leakage point. In order to enhance the leakage estimation capability of a buried pipe in a noisy environment, an improved cross-correlation technique is proposed. It uses a noise rejection technique in the frequency domain to effectively eliminate the tonal noise due to rotating machinery. Experiments were carried out to verify the validity of the proposed method. The results show that even in a tonal noisy environment, the proposed method can provide more reliable means for estimating the time delay of the leakage signals.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1998년도 학술발표대회 논문집 제17권 1호
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• pp.357-360
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• 1998

DS/CDMA system rejected narrow-band interference and additional White Gaussian noise which are occured at multipath, intentional jammer and multiuser to share same bandwidth in mobile communication systems. Because of having not sufficiently obtained processing gain which is related to system performance, they were not effectively suppressed. In this paper, an matched filter channel model using backpropagation neural network based on complex multilayer perceptron is presented for suppressing interference of narrow-band of direct sequence spread spectrum receiver in DS/CDMA mobile communication systems. Recursive least square backpropagation algorithm with backpropagation error is used for fast convergence and better performance in matched filter receiver scheme. According to signal noise ratio and transmission power ratio, computer simulation results show that bit error ratio of matched filter using backpropagation neural network improved than that of RAKE receiver of direct sequence spread spectrum considering of con-channel and narrow-band interference.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.1150-1153
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• 2006

Many commercial high speed and lightly loaded rotating machineries incorporate floating ring bearings (FRBs) owing to their low cost and reduced power losses. Many researchers have developed various analytical models to predict the performance and the stability of those rotor-bearing systems with FRBs. However, most of the models failed to predict stability of the rotor-bearing systems with FRBs. FRBs comprise two fluid films in series and the ratio of floating ring speed to journal speed reflects the equilibrium state of the two fluid films. Therefore the speed ratio is one of the main concerns in the analysis of FRBs. This paper provides the experimental results of the speed ratio which enables one to verify of the analysis model for FRBs.

• Journal of Communications and Networks
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• 제18권1호
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• pp.19-26
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• 2016

In this paper, the performance of dual-hop multi-relay maximum ratio transmission (MRT) over Rayleigh flat fading channels is studied with both conventional (all relays participate the transmission) and opportunistic (best relay is selected to maximize the received signal-to-noise ratio (SNR)) relaying. Performance analysis starts with the derivation of the probability density function, cumulative distribution function and moment generating function of the SNR. Then, both approximate and asymptotic expressions of symbol error rate (SER) and outage probability are derived for arbitrary numbers of antennas and relays. With the help of asymptotic SER and outage probability, diversity and array gains are obtained. In addition, impact of imperfect channel estimations is investigated and optimum power allocation factors for source and relay are calculated. Our analytical findings are validated by numerical examples which indicate that multi-relay MRT can be a low complexity and reliable option in cooperative networks.

• 한국통신학회논문지
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• 제35권4A호
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• pp.315-321
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• 2010

Ad-hoc 네트워크에서는 전력을 제어할 기지국의 부재로 시스템의 성능을 최적화 시키는 중앙 전력 제어가 불가능하여, 각 노드들은 독립적이고 자동적인 방식으로 분산형 전력 제어 알고리즘을 수행해야 한다. 기존의 분산형 전력 제어 알고리즘은 수신 신호의 SINR (signal to interference and noise ratio)에 따라 MCS (modulation and coding scheme) 레벨을 변화 시키는 adaptive bit loading operation을 고려하지 않기 때문에, 전체 throughput 향상에 제한이 있다. 본 논문에서는 Ad-hoc 환경에서 전체 throughput 을 향상시키고, outage 확률을 낮추기 위해 MCS 레벨에 따라 adaptive bit loading operation을 고려한 분산형 전력 제어 알고리즘을 제안한다. 컴퓨터 모의실험 결과 매우 큰 throughput 향상과 outage 확률 감소의 성능 향상을 확인할 수 있다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 통신소사이어티 추계학술대회논문집
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• pp.251-254
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• 2003

In this paper, we develop an effective method for estimating and predicting interference power strength using the IMM(Interacting Multiple Model) algorithm. Based on the proposed interference prediction algorithm, we adjust transmission power of mobile terminals to maintain a certain level of target signal - to - interference- plus -noise- ratio ( SINR ) at the base station. Results of numerical experiments are presented to show a performance profile of the proposed algorithm.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권6호
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• pp.1418-1432
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• 2013

This paper studies the problem of secure information exchange between two sources via multiple relays in the presence of an eavesdropper. To this end, we propose a relay beamforming scheme, i.e., relay beamforming with artificial noise (RBwA), where the relay beamforming vector and the artificial noise vector are jointly designed to maintain the received signal-to-interference-ratio (SINR) at the two sources over a predefined Quality of Service (QoS) threshold while limiting the received SINR at the eavesdropper under a predefined secure threshold. For comparison, the relay beamforming without artificial noise (RBoA) is also considered. We formulate two optimization problems for the two schemes, where our goal is to seek the optimal beamforming vector to minimize the total power consumed by relay nodes such that the secrecy of the information exchange between the two sources can be protected. Since both optimization problems are nonconvex, we solve them by semidefinite program (SDP) relaxation theory. Simulation results show that, via beamforming design, physical layer secrecy of two-way relay networks can be greatly improved and our proposed RBwA outperforms the RBoA in terms of both low power consumption and low infeasibility rate.