• Current Optics and Photonics
• /
• 제1권3호
• /
• pp.196-202
• /
• 2017

Corona discharge is always a sign of failure processes of high-voltage electrical apparatus, including those utilized in electric railway systems. Solar-blind ultraviolet (UV) cameras are effective tools for corona inspection. In this work, we present an automatic railway corona-discharge detection system based on solar-blind ultraviolet detection. The UV camera, mounted on top of a train, inspects the electrical apparatus, including transmission lines and insulators, along the railway during fast cruising of the train. An algorithm based on the Hough transform is proposed for distinguishing the emitting objects (corona discharge) from the noise. The detection system can report the suspected corona discharge in real time during fast cruises. An experiment was carried out during a routine inspection of railway apparatus in Xinjiang Province, China. Several corona-discharge points were found along the railway. The false-alarm rate was controlled to less than one time per hour during this inspection.

• 한국통신학회논문지
• /
• 제30권3C호
• /
• pp.153-157
• /
• 2005

이동 통신 시스템에서 도플러 효과에 의해 주파수 선택적 페이딩 현상이 발생한다. DS-CDMA 시스템은 주파수 선택적 채널 하에서 다중 사용자 간섭의 영향에 의해서 성능이 급격하게 저하 된다. 이를 극복하기 위해서 다중 반송파 변조 방법을 채택하여 주파수 선택적 채널 효과를 극복할 수 있다. 그리고 다중 사용자 접속으로 인한 간섭 문제는 다중 사용자 검출 기법을 적용하여 해결 할 수 있다. 본 논문에서는 블라인드 다중 사용자 검출 기법과 병렬 간섭 제거기를 결합한 형태의 블라인드 MOE-PIC 다중 사용자 검출 기법을 제안하였다. 모의실험 결과 제안한 방식이 기존의 방식보다 더 좋은 성능을 나타내는 것을 알 수 있었다.

• Journal of Communications and Networks
• /
• 제8권3호
• /
• pp.290-296
• /
• 2006

In this paper, a generalized blind adaptive algorithm is introduced for multi-user detection of direct sequence code division multiple access (OS-COMA) wireless communication systems. The main property of the proposed algorithm is its ability to resolve the multipath fading channel resulting in inter symbol interference (ISI) as well as multiple access interference (MAI). Other remarkable properties are its low complexity and mitigation to the near-far problem as well as its insensitivity to asynchronous transmission. The proposed system is based on the minimization of the output energy and convergence to the minimum mean square error (MMSE) detector. It is blind in the sense that it needs no knowledge of the other users' signatures, only the intended user signature and timing are required. Furthermore, the convergence of the minimum output energy (MOE) detector to the MMSE detector is analytically proven in case of M-ary PSK. Depicted results show that the performance of the generalized system dominates those previously considered. Further improvements are obtained when multiple input multiple output (MIMO) technique is employed.

• Journal of Information Processing Systems
• /
• 제13권2호
• /
• pp.385-399
• /
• 2017

Nowadays, with the development of signal processing technique, the protection to the integrity and authenticity of images has become a topic of great concern. A blind image authentication technology with high tamper detection accuracy for different common attacks is urgently needed. In this paper, an improved fragile watermarking method based on local binary pattern (LBP) is presented for blind tamper location in images. In this method, a binary watermark is generated by LBP operator which is often utilized in face identification and texture analysis. In order to guarantee the safety of the proposed algorithm, Arnold transform and logistic map are used to scramble the authentication watermark. Then, the least significant bits (LSBs) of original pixels are substituted by the encrypted watermark. Since the authentication data is constructed from the image itself, no original image is needed in tamper detection. The LBP map of watermarked image is compared to the extracted authentication data to determine whether it is tampered or not. In comparison with other state-of-the-art schemes, various experiments prove that the proposed algorithm achieves better performance in forgery detection and location for baleful attacks.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제10권12호
• /
• pp.5643-5656
• /
• 2016

The detection accuracy of steganalysis depends on many factors, including the embedding algorithm, the payload size, the steganalysis feature space and the properties of the cover source. In practice, the cover source mismatch (CSM) problem has been recognized as the single most important factor negatively affecting the performance. To address this problem, we propose a new framework for blind, universal steganalysis which uses traditional steganalyst features. Firstly, cover images with the same statistical properties are searched from a reference image database as aided samples. The test image and its aided samples form a whole test set. Then, by assuming that most of the aided samples are innocent, we conduct outlier detection on the test set to judge the test image as cover or stego. In this way, the framework has removed the need for training. Hence, it does not suffer from cover source mismatch. Because it performs anomaly detection rather than classification, this method is totally unsupervised. The results in our study show that this framework works superior than one-class support vector machine and the outlier detector without considering the image retrieval process.

• ETRI Journal
• /
• 제31권2호
• /
• pp.193-200
• /
• 2009

In this paper, we study the performance of subspace-based multiuser detection techniques for multicarrier code-division multiple access (MC-CDMA) systems. We propose an improvement in the PASTd algorithm by cascading it with the classical Gram-Schmidt procedure to orthonormalize the eigenvectors after their sequential extraction. The tracking of signal subspace using this algorithm, which we call OPASTd, has a faster convergence as the eigenvectors are orthonormalized at each discrete time sample. This improved PASTd algorithm is then used to implement the subspace blind adaptive multiuser detection for MC-CDMA. We also show that, for multiuser detection, the complexity of the proposed scheme is lower than that of many other orthogonalization schemes found in the literature. Extensive simulation results are presented and discussed to demonstrate the performance of the proposed scheme.

• 전자공학회논문지 IE
• /
• 제43권2호
• /
• pp.75-79
• /
• 2006

블라인드 기법은 훈련열 없이 검출하고자 하는 사용자의 최소한의 정보만을 가지고 정보 검출이 가능한 방법이다. 본 논문에서는 직접 대역 확산 코드 분할 다중 접속 시스템에서 다중사용자 간섭을 제거하기 위해서, 혼합된 비용함수를 사용하는 블라인드 다중사용자 검출기를 제안하였다. 제안된 블라인드 다중사용자 검출기의 비용함수는 LMS와 LMF를 혼합한 형태로 이루어져있으며, 제안된 다중사용자 검출기의 성능을 평가하기 위해서 가우시안 채널 하에서 BER을 비교 하였다. 모의실험 결과, 사용자가 20 명 존재하는 경우, 제안된 블라인드 검출기가 블라인드 MOE 다중사용자 검출기에 비해 약 3dB정도 더 나은 성능을 지님을 확인 할 수 있었다.

• 대한전자공학회논문지SD
• /
• 제49권7호
• /
• pp.10-16
• /
• 2012

본 논문에서는 협대역 간섭 광학 필터(narrow band interference optical filter)를 적용하여 광학적 잡음에 내성이 강한 차세대용 마일즈 감지 시스템을 구현하고자 시도하였다. 900nm의 레이저 파장에 대해 파장범위(wavelength range) 895~915nm의 협대역 간섭 광학 필터를 적용한 결과 시가전 상황에서 발생할 수 있는 강한 광학적 잡음에 내성을 갖는 감지 특성을 얻을 수 있었다. 그러나 청색천이(blue shift) 현상에 의해 마일즈 감지 시스템에 입사각 $30^{\circ}{\sim}90^{\circ}$ 구간에 감지 사각 영역이 발생하였다. 이 문제를 해결하기위해 굴절체를 이용한 입사각 산란 방법을 제안하였고, 디옵터 5.4의 오목 메니스커스 렌즈 굴절체(concave meniscus lens refractor)를 마일즈 감지 시스템에 적용하여 입사각을 산란시킨 결과 감지 사각을 없앨 수 있었다.

• ETRI Journal
• /
• 제42권1호
• /
• pp.26-35
• /
• 2020

Herein, we consider uplink multiuser massive multiple-input multiple-output systems when multiple users transmit information symbols to a base station (BS) by applying simple space-time block coding (STBC). At the BS receiver, two detection filters for each user are used to detect the STBC information symbols. One of these filters is for odd-indexed symbols and the other for even-indexed symbols. Using constrained output variance metric minimization, we first derive a special relation between the closed-form optimal solutions for the two detection filters. Then, using the derived special relation, we propose a new blind adaptive algorithm for implementing the minimum output variance-based optimal filters. In the proposed adaptive algorithm, filter weight vectors are updated only in the region satisfying the special relation. Through a theoretical analysis of the convergence speed and a computer simulation, we demonstrate that the proposed scheme exhibits faster convergence speed and lower steady-state bit error rate than the conventional scheme.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2005년도 학술대회 논문집 정보 및 제어부문
• /
• pp.445-447
• /
• 2005

MCMA(modified constant modulus algorithm) accomplishes blind equalization and carrier phase recovery simultaneously. But, the error level of MCMA is not zero when the equalizer converges completely. Because the MCMA uses a special signal point instead of a original signal point. MCMA-DO(decision-directed) improves the steady-state performance but the performance of equalizer is decided by switching time between the MCMA and the DD. In this paper, according to the residual ISI(intersymbol interference) of the equalizer output, the most suitable switching time is decided automatically.