• Title, Summary, Keyword: Asynchronous detection

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A Study on the Detection of Asynchronous State of the Synchronous Generator

  • Choi, Hyung-Joo;Lee, Heung-Ho
    • Journal of international Conference on Electrical Machines and Systems
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    • v.2 no.4
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    • pp.405-412
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    • 2013
  • This paper includes new protection concepts and practices to avoid mechanical damage of three-phase transformer by asynchronous operation of synchronous generator. this failure is often caused just after synchronous generator was connected to the grid because of a malfunction of the controller or misconnections of the synchronous devices. The results of the studies on the analyzing the phenomenon of asynchronous operation experienced in Korea and rapidly detecting asynchronous state are descrived.

Performance of Multicarrier-CDMA Uplink with Antenna Arrays and Multiuser Detection

  • Sigdel, Shreeram;Ahmed, Kazi M.;Fernando, Anil
    • Journal of Communications and Networks
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    • v.5 no.2
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    • pp.150-156
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    • 2003
  • In this paper, an uplink MC-CDMA system incorporating multiuser detection and smart antennas has been considered. The performance of asynchronous as well as synchronous system is studied over a correlated Rayleigh multipath slow fading channel. A simplified array-processing algorithm suitable for slow fading situation is investigated to overcome the heavy computational complexity associated with Eigen solutions. The effect of variable data rate in the system performance is considered and effectiveness of antenna array to handle high data rate is discussed. A brief investigation on the system performance degradation due to correlated channel is also carried out. Based on the extensive simulation carried out, the performance of the asynchronous uplink system is found dramatically improved with antenna array and multiuser detection. Asynchronicity and channel correlation are found to affect the system performance significantly. The investigated simpli- fied algorithm produces similar results as Eigen solutions in slow fading situation with much reduced complexity.

Analysis of the range estimation error of a target in the asynchronous bistatic sonar (비동기 양상태 소나의 표적 거리 추정 오차 분석)

  • Jeong, Euicheol;Kim, Tae-Hwan
    • The Journal of the Acoustical Society of Korea
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    • v.39 no.3
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    • pp.163-169
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    • 2020
  • The asynchronous bistatic sonar needs to estimate direct blast arrival time at a receiver to localize targets, and therefore the direct blast arrival time estimation error could be added to target localization error in comparison with synchronous system. Direct blast especially appears as several peaks at the matched filter output by multipath, thus we compared the first peak detection technique and the maximum peak detection technique of those peaks for direct blast arrival time estimation through sea trial data. The test was performed in a shallow sea with bistatic sonar made up of spatially separated source and line array sensors. Line array sensors obtained the target signal which is generated from the echo repeater. As a result, the first peak detection technique is superior to maximum peak detection technique in direct blast arrival time estimation error. The result of this analysis will be used for further research of target tracking in the asynchronous bistatic sonar.

Robust Process Fault Detection System Under Asynchronous Time Series Data Situation (비동기 설비 신호 상황에서의 강건한 공정 이상 감지 시스템 연구)

  • Ko, Jong-Myoung;Choi, Ja-Young;Kim, Chang-Ouk;Sun, Sang-Joon;Lee, Seung-Jun
    • IE interfaces
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    • v.20 no.3
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    • pp.288-297
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    • 2007
  • Success of semiconductor/LCD industry depends on its yield and quality of product. For the purpose, FDC (Fault Detection and Classification) system is used to diagnose fault state in main manufacturing processes by monitoring time series data collected by equipment sensors which represent various conditions of the equipment. The data set is segmented at the start and end of each product lot processing by a trigger event module. However, in practice, segmented sensor data usually have the features of data asynchronization such as different start points, end points, and data lengths. Due to the asynchronization problem, false alarm (type I error) and missed alarm (type II error) occur frequently. In this paper, we propose a robust process fault detection system by integrating a process event detection method and a similarity measuring method based on dynamic time warping algorithm. An experiment shows that the proposed system is able to recognize abnormal condition correctly under the asynchronous data situation.

A Time-Varying Modified MMSE Detector for Multirate CDMA Signals in Fast Rayleigh Fading Channels

  • Jeong, Kil-Soo;Yokoyama, Mitsuo;Uehara, Hideyuki
    • ETRI Journal
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    • v.29 no.2
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    • pp.143-152
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    • 2007
  • In this paper, we propose a time-varying modified minimum mean-squared error (MMSE) detector for the detection of higher data rate signals in a multirate asynchronous code-division multiple-access (CDMA) system which is signaled in a fast Rayleigh fading channel. The interference viewed by a higher data rate symbol will be periodic due to the presence of a lower data rate symbol which spans multiple higher data rate symbols. The detection is carried out on the basis of a modified MMSE criterion which incorporates differential detection and the ratio of channel coefficients in two consecutive observation intervals inherently compensating the fast variation of the channel due to fading. The numerical results obtained by the MMSE detector with time-varying detection show around 3 dB (M=2) and 6 dB (M=4) performance improvement at a BER of $10^{-3}$ in the AWGN channel, while introducing more computational complexity than the MMSE detector without time-varying detection. At a higher $E_b/N_0$, the proposed scheme can achieve a BER of approximately $10^{-3}$ in the presence of fast channel variation which is an improvement over other schemes.

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Direct blast detection algorithm for asynchronous bistatic sonar systems (비동기 양상태 소나 시스템을 위한 직접파 탐지 기법)

  • Jeong, Euicheol;Ahn, Jae-Kyun;Kim, Juho
    • The Journal of the Acoustical Society of Korea
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    • v.37 no.3
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    • pp.139-146
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    • 2018
  • Monostatic sonar systems localize targets using the time information of pulse transmission and receipt. Whereas, in asynchronous bistatic sonar systems, receivers need to detect direct blast to localize targets, since a source doesn't share pulse information with receivers. In this paper, we propose a direct blast detection algorithm, which estimates PRI (Pulse Repetition Interval) of direct blast and adaptive thresholds. Experimental results show the proposed algorithm has robust direct blast detection performance in the environment where strong background noise and target signal exist.

Mitigation Techniques of Channel Collisions in the TTFR-Based Asynchronous Spectral Phase-Encoded Optical CDMA System

  • Miyazawa, Takaya;Sasase, Iwao
    • Journal of Communications and Networks
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    • v.11 no.1
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    • pp.1-10
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    • 2009
  • In this paper, we propose a chip-level detection and a spectral-slice scheme for the tunable-transmitter/fixed-receiver (TTFR)-based asynchronous spectral phase-encoded optical codedivision multiple-access (CDMA) system combined with timeencoding. The chip-level detection can enhance the tolerance of multiple access interference (MAI) because the channel collision does not occur as long as there is at least one weighted position without MAI. Moreover, the spectral-slice scheme can reduce the interference probability because the MAI with the different frequency has no adverse effects on the channel collision rate. As a result, these techniques mitigate channel collisions. We analyze the channel collision rate theoretically, and show that the proposed system can achieve a lower channel collision rate in comparison to both conventional systems with and without the time-encoding method.

Decision Statistics for Noncoherent Serial PN Code Acquisition In Chip-Asynchronous DS/SS Systems (칩비동기 직접수열 대역확산 시스템에서 비동기 직렬 의사잡음코드 포착을 위한 결정통계량)

  • 윤석호;김선용
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.41 no.5
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    • pp.19-25
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    • 2004
  • In this paper, we propose optimal and suboptimal serial code acquisition schemes for chip-asynchronous direct-sequence spread-spectrum systems. The conventional serial code acquisition scheme is to compare each value of correlator outputs with a threshold individually. However, such a scheme is optimum only under the chip-synchronous assumption which is actually very difficult to be held prior to acquisition at the receiver because the signal-to-noise ratios before despreading are very low. In this paper, an optimal serial code acquisition scheme is derived based on the maximum-likelihood criterion under the more realistic and general chip-asynchronous environments. A suboptimal scheme, which is simpler but yields comparable performance to the optimal one, is also derived based on the criterion of local detection power Numerical results show that, under the chip-asynchronous environments, both the optimal and suboptimal serial code acquisition schemes outperform the conventional serial code acquisition scheme.

Asynchronous Multilevel Search Strategy for Fast Acquisition of AltBOC Signals

  • Kim, Binhee;Kong, Seung-Hyun
    • Journal of Positioning, Navigation, and Timing
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    • v.4 no.4
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    • pp.161-171
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    • 2015
  • Alternative binary offset carrier (AltBOC) signals can be approximated by four synchronized direct sequence spread spectrum (DSSS) signals, each pair of which is a quadrature phase shift keyed (QPSK) signal at a different frequency. Therefore, depending on the strength of an incoming AltBOC signal, an acquisition technique can reduce the mean acquisition time (MAT) by searching the four DSSS signals asynchronously; the search for each of the four DSSS signals can start at one of the evenly separated hypotheses on the two-dimensional hypothesis space. And detection sensitivity can be improved by multiple levels when different numbers of search results for the same hypothesis are combined. In this paper, we propose a fast AltBOC acquisition technique that has an asynchronous search strategy and efficiently utilizes the output of the four search results to increase the sensitivity level when sensitivity improvement is needed. We provide a complete theoretical analysis and demonstrate with numerous Monte Carlo simulations that the MAT of the proposed technique is much smaller than conventional AltBOC acquisition techniques.

Robust State Feedback Control of Asynchronous Machines with Intermittent Faults (간헐 고장이 존재하는 비동기 머신의 견실한 상태 피드백 제어)

  • Yang, Jung-Min
    • Journal of the Institute of Electronics Engineers of Korea SC
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    • v.48 no.3
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    • pp.40-47
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    • 2011
  • This paper addresses the problem of fault detection and tolerance for asynchronous sequential machines using state feedback control. The considered asynchronous machine is affected by intermittent faults. When intermittent faults occur, the machine undergoes unauthorized state transitions and, for a finite duration, remains at the fault state, not responding to the change of the external input. In this paper, we postulate the scheme of detecting intermittent faults and present the existence condition and design algorithm for a robust state feedback controller that overcomes the adversarial effect of intermittent faults. We also undertake a comparative study between the previous control scheme for transient faults and the present strategy for intermittent faults. The design procedure for the proposed controller is described in a case study.