• Title/Summary/Keyword: directional noise

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Analysis of GNSS PPP Positioning Errors Due to Strong Geomagnetic Storm on May 11, 2024 (2024년 5월 11일 강한 지자기 폭풍에 의한 GNSS PPP 측위 오차 분석)

  • Byung-Kyu Choi;Junseok Hong;Dong-Hyo Sohn;Sul Gee Park;Sang Hyun Park
    • Journal of Positioning, Navigation, and Timing
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    • v.13 no.3
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    • pp.269-275
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    • 2024
  • On May 11, 2024, there was a strong solar flare explosion. A powerful geomagnetic storm triggered by a solar flare caused a major ionospheric disturbance over the Korean Peninsula. When a geomagnetic storm occurred, an abnormal change in vertical total electron content (VTEC) values was detected at all Global Navigation Satellite System (GNSS) stations in the Korean Peninsula. In addition, we performed GNSS precise point positioning (PPP) processing using observations from the SBAO and MKPO stations. We found that the up-directional position error increased significantly in both stations at around 17:00 UT on the day of year (DOY) 132, 2024. At that point, the root mean square (RMS) values for all position errors (East, North, and Up) increased compared to other dates. Due to very high noise, the L1 signal-to-noise ratio (SNR) values of QZSS pseudo-random noise (PRN) 07 dropped to about 25 dB. As a result, we suggest that the strong geomagnetic storm increased the GNSS PPP position errors in the Korean Peninsula.

Bearing Estimation of Narrow Band Acoustic Signals Using Cardioid Beamforming Algorithm in Shallow Water

  • Chang, Duk-Hong;Park, Hong-Bae;Na, Young-Nam;Ryu, Jon-Ha
    • The Journal of the Acoustical Society of Korea
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    • v.21 no.2E
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    • pp.71-80
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    • 2002
  • This paper suggests the Cardioid beamforming algorithm of the doublet sensors employing DIFAR (directional frequency analysis and recording) sensor signals in the frequency domain. The algorithm enables target bearing estimation using the signals from directional sensors. The algorithm verifies its applicability by successfully estimating bearings of a target projecting ten narrow-band signals in shallow water. The estimated bearings agree very well with those from GPS (global positioning system) data. Assuming the bearings from GPS data to be real values, the estimation errors are analyzed statistically. The histogram of estimation errors in each frequency have Gaussian shape, the mean and standard deviation dropping in the ranges -1.1°∼ 6.7°and 13.3∼43.6°, respectively. Estimation errors are caused by SNR (signal to noise ratio) degradation due to propagation loss between the source and receiver, daily fluctuating geo-magnetic fields, and non-stationary background noises. If multiple DIFAR systems are employed, in addition to bearing, range information could be estimated and finally localization or tracking of a target is possible.

Symmetry Detection Through Hybrid Use Of Location And Direction Of Edges

  • Koo, Ja Young
    • Journal of the Korea Society of Computer and Information
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    • v.21 no.4
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    • pp.9-15
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    • 2016
  • Symmetry is everywhere in the world around us from galaxy to microbes. From ancient times symmetry is considered to be a reflection of the harmony of universe. Symmetry is not only a significant clue for human cognitive process, but also useful information for computer vision such as image understanding system. Application areas include face detection and recognition, indexing of image database, image segmentation and detection, analysis of medical images, and so on. The technique used in this paper extracts edges, and the perpendicular bisector of any two edge points is considered to be a candidate axis of symmetry. The coefficients of candidate axis are accumulated in the coefficient space. Then the axis of symmetry is determined to be the line for which the coefficient histogram has maximum value. In this paper, an improved method is proposed that utilizes the directional information of edges, which is a byproduct of the edge detection process. Experiment on 20 test images shows that the proposed method performs 22.7 times faster than the original method. In another test on 5 images with 4% salt-and-pepper noise, the proposed method detects the symmetry successfully, while the original method fails. This result reveals that the proposed method enhances the speed and accuracy of detection process at the same time.

Fingerprint Recognition System for On-line User Authentication (온라인 사용자 인증을 위한 지문인식 시스템)

  • Han, Sang-Hoon;Lee, Ho;Seo, Jeong-Man
    • Journal of the Korea Society of Computer and Information
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    • v.11 no.1 s.39
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    • pp.283-292
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    • 2006
  • Interest about a latest security connection technology rises, and try to overcome security vulnerability Certification about on-line user methods through fingerprint that is biometries information apply. In this study, designs and implements fingerprint recognition system that is invariant to rotation by fingerprint recognition system for certification about on-line user. Proposed method focused in matching process through pre-process of fingerprint image, feature point extraction. Improved process time and correct recognition rate in fingerprint recognition system that is invariant to rotation presented in existing study. Also, improved noise, distortion problems that happen in preprocess of existing study applying directional Laplacian filter.

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Heartbeat Detection based on Signal Reflected from Antenna in Mobile Device (휴대기기에서의 안테나 반사 신호를 이용한 심박 신호 검출)

  • An, Yong-Jun;Yun, Gi-Ho;Yook, Jong-Gwan
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.38C no.7
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    • pp.643-649
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    • 2013
  • In this paper, human heartbeat detection using signal reflected from the antenna which is varied reflection coefficient by near field variation of the antenna. For detection reflected signal from antenna, 20 dB directional coupler is used because of not affecting transmitting signal. Variance of reflection coefficient of dipole antenna is about 0.07 dB which is too small the distinction between heartbeat and noise. Sensitivity increasing method is applied and heartbeat is clearly detected. Due to phase and magnitude errors come from discrete value components, antenna is located some points in experiments ro find optimum sensitivity position. And providing verification of using communication signal, heartbeat detection when frequency modulated signal which have 4 MHz bandwidth is applied.

GPS Pull-In Search Using Reverse Directional Finite Rate of Innovation (FRI)

  • Kong, Seung-Hyun;Yoo, Kyungwoo
    • Journal of Positioning, Navigation, and Timing
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    • v.3 no.3
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    • pp.107-116
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    • 2014
  • When an incoming Global Positioning System (GPS) signal is acquired, pull-in search performs a finer search of the Doppler frequency of the incoming signal so that phase lock loop can be quickly stabilized and the receiver can produce an accurate pseudo-range measurement. However, increasing the accuracy of the Doppler frequency estimation often involves a higher computational cost for weaker GPS signals, which delays the position fix. In this paper, we show that the Doppler frequency detectable by a long coherent auto-correlation can be accurately estimated using a complex-weighted sum of consecutive short coherent auto-correlation outputs with a different Doppler frequency hypothesis, and by exploiting this we propose a noise resistant, low-cost and highly accurate Doppler frequency and phase estimation technique based on a reverse directional application of the finite rate of innovation (FRI) technique. We provide a performance and computational complexity analysis to show the feasibility of the proposed technique and compare the performance to conventional techniques using numerous Monte Carlo simulations.

The Bearing Estimation of Narrowband Acoustic Signals Using DIFAR Beamforming Algorithm (DIFAR 빔형성 알고리듬을 이용한 협대역 음향신호의 방향성 추정)

  • 장덕홍;박홍배;정문섭;김인수
    • Journal of the Korea Institute of Military Science and Technology
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    • v.5 no.2
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    • pp.169-184
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    • 2002
  • In order to extract bearing information from the directional sensors of DIFAR(directional frequency analysis and recording) that is a kind of passive sonobuoy, the cardioid beamforming algorithm applicable to DIFAR system was studied in the frequency domain. the algorithm uses narrow-band signals propagated though the media from the acoustic sources such as ship machineries. The proposed algorithm is expected to give signal to noise ratio of 6dB when it uses the maximum response axis(MRA) among the Cardioid beams. The estimated bearings agree very well with those from GPS data. Assuming the bearings from GPS data to be real values, the estimation errors are analyzed statistically. The histogram of estimation errors in each frequency have Gaussian shape, the mean and standard deviation dropping in the ranges -1.1~$6.7^{\circ}$ and 13.3~$43.6^{\circ}$, respectively. Estimation errors are caused by SMR degradation due to propagation loss between the source and receiver, daily fluctuating geo-magnetic fields, and non-stationary background noises. If multiple DIFAR systems are employed, in addition to bearing, range information could be estimated and finally localization or tracking of a target is possible.

A Study on Dynamic Characteristics of a Catenary System (가선계의 동특성에 관한 연구)

  • 김정수;최병두
    • Journal of KSNVE
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    • v.9 no.2
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    • pp.317-323
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    • 1999
  • Dynamic characteristics of catenary that supplies electrical power to high-speed trains are investigated. A simple catenary is composed of the contact and messenger wires connected by droppers possessing bi-directional stiffness properties. For slender, repeating structures such as catenary, both the wave propagation and vibration properties need to be understood. The influence of parameters that determine catenary dynamics are investiaged through numerical simulations involving finite element models. The effects of the tension and flexural rigidity of the contact wire is first investigated. The effects of dropper characteristics are then investigated. For linear droppers wave propagation as well as modal properties are determined. For large catenary motion, droppers can be modeled as bi-directional elements possessing low stiffness in compression and high stiffness in tension. For this case, impulse response is computed and compared with the cases of linear droppers. It is found that the catenary dynamics are primarily determined by contact wire tension and dropper properties, with large responses observed in 5∼40 Hz frequency range. In particular, the dropper stiffness and spacing are found to have dominant influence on the response frequency and the wave transmission characteristics.

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Directional Winger-Ville Distribution and Its Application to Rotating- Machinery (방향성 Winger-Ville 분포와 회전체에의 응용)

  • Kim, Dong-Wan
    • Journal of KSNVE
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    • v.6 no.3
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    • pp.341-347
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    • 1996
  • Vibration analysis is one of the most powerful tools available for the detection and isolation of incipient faults in mechanical systems. The methods of vibration analysis in use today and under continuous study are broad band vibration monitoring, time domain analysis, and frequency domain analysis. In recent years, great interest has been generated concerning the use of time- frequency repesentation and its application for a machinery diagnostics and condition monitoring system. The objective of the study described in this paper was to develop a new diagnostic tool for the rotating machinery. This paper introduces a new time frequency representation. Directional Winger-Ville Distribution, which analyese the time-frequency structure of the rotating machinery vibration.

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A Real Time Deblocking Technique Using Adaptive Filtering in a Mobile Environment (모바일 환경에서 적응적인 필터링을 이용한 실시간 블록현상 제거 기법)

  • Yoo, Jae-Wook;Park, Dae-Hyun;Kim, Yoon
    • The Journal of Korean Association of Computer Education
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    • v.13 no.4
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    • pp.77-86
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    • 2010
  • In this paper, we propose a real time post-processing visual enhancement technique to reduce the blocking artifacts in block based DCT decoded image for mobile devices that have allocation of the restricted resource. In order to reduce the blocking artifacts effectively even while preserving the image edge to the utmost, the proposed algorithm uses the deblocking filtering or the directional filtering according to the edge detection of the each pixel. After it is discriminated that the pixel to apply the deblocking filtering belongs again to the monotonous area, the weighted average filter with the adaptive mask is applied for the pixel to remove the blocking artifacts. On the other hand, a new directional filter is utilized to get rid of staircase noise and preserve the original edge component. Experimental results show that the proposed algorithm produces better results than those of the conventional algorithms in both subjective and objective qualities.

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