• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6C
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• pp.623-628
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• 2006

This paper addresses the frequency offset estimation problem in the presence of the timing error for OFDM systems. When the timing error exists, the correlation value used for the frequency offset estimation could be reduced significantly due to the timing error, resulting in considerable degradation in estimation performance. In this paper, using the coherence phase bandwidth (CPB) and a threshold, a novel frequency offset estimation scheme is proposed and based on which, an efficient timing error estimation scheme is also proposed for the re-estimation of the frequency offset. The performance comparison results show that the proposed frequency offset estimation scheme is not only more robust to the timing error but also has less computational complexity, as compared with the conventional schemes. It is also demonstrated by simulation that theproposed timing error estimation scheme gives a reliable estimate of the timing error.

• 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.

• Journal of Korea Society of Industrial Information Systems
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• v.4 no.1
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• pp.110-116
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• 1999

In this paper, signal processing is utilized to reduce the computational time which is one of weak point of FDTD(finite difference time domain) method. Compared with the direct FDTD. combination of FDTD and signal processing achieves the same type of accuracy in much shorter time The combination method spends 140 minutes to analyze the frequence characteristics of the microstrip lowpass filter while the direct FDTD consumes about 900 minutes. To verify the obtained results, microstrip lowpass filter is fabricated on dielectric substrate and the measured results are compared with the analyzed results. It is shown that measured results are in good agreement with the theoretical results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.11
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• pp.1156-1160
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• 2003

Many time-frequency analysis techniques have been used for motion compensated ISAR(Inverse Synthetic Aperture Radar) imaging. In this work, a novel time-frequency(T-F) analysis called evolutionary adaptive wavelet transform (EAWT) and evolutionary adaptive joint time-frequency(EAJTF) procedure are used for the motion compensated ISAR image. To show the validity of our algorism, we use simulated MIG-25 and Boeing 727(B-727) ISAR data. From the constructed ISAR image using EAWT and EAJTF, we show that our algorithm can obtain a clear motion compensated ISAR image such as other time-frequency analysis techniques.

• Proceedings of the Acoustical Society of Korea Conference
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• 1996.06a
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• pp.29-32
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• 1996

본 논문에서는 시변 주파수를 추정하기 위한 방법으로 기존의 시간 가중 칼만 추정기법에 변형된 Huber함수를 적용하여 충격성 잡음환경 하에서도 강인한 칼만추정기법을 제안하였다. 기존의 시간 가중 칼만 추정기법은 오차가 정규분포를 가진다고 가정된 상태에서는 적합한 파라메타 추정을 할 수 있지만 충격성 잡음이 존재하는 경우에는 수렴속도나 시변적응능력에서의 성능저하가 나타난다. 제안된 알고리듬은 영향함수 측면에서 충격성 잡음에 의해 생기는 오차의 크기를 제한함으로써 기포나 인위적인 충격성 잡음환경 하에서도 시변 주파수 추정을 할 수 있으며 알고리듬의 타당성은 모의실험을 통해 보였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.8
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• pp.488-490
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• 2014

This paper deals with distributed time and frequency synchronization algorithms using the flocking technique for OFDMA-based wireless mesh networks. We propose a time and frequency synchronization model taking into account channel propagation delays existing in wireless mesh networks, and analyze the convergence condition of the proposed synchronization algorithm. Convergence performance of the proposed synchronization algorithm is analyzed via computer simulation in terms of synchronization parameters in the time and frequency synchronization model.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.2
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• pp.191-200
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• 2013

In this paper, we propose a new estimation method of time offset, frequency offset, and signal to interference plus noise ratio (SINR) using the synchronization channel preamble to provide IEEE 802.16.1a based talk-around direct communications (TDC). The proposed scheme estimates the time offset and frequency offset both in the time domain and in the frequency domain considering the preamble structure. In addition, it improves the estimation accuracy by combining the estimated values in two domains taking into account TDC synchronization scenarios. Through numerical simulations in the TDC channel environments, the performance of the proposed algorithm is compared with those of existing techniques such as the time domain estimation and the frequency domain estimation.

• Proceedings of the IEEK Conference
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• 2000.09a
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• pp.479-482
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• 2000

다중경로 채널의 시변 특성은 OFDM(orthogonal frequency division multiplexing) 신호의 직교성을 파괴시키며 이는 인접 채널간 간섭(ICI: interchannel interference)을 발생시켜 도플러 주파수에 비례하는 오류를 발생시킨다. 본 논문에서는 채널 시변의 원인을 주파수 옵셋과 도플러효과로 규정하고, 주파수 옵셋을 보정하기 위해 기존의 선형보간법(LI: linear interpolation method)대신 선형위상보간법(LPI: linear phase interpolation)과 도플러효과에 의한 ICI 를 제거하기 위해 기존의 주파수영역 등화기법보다 효과적인 시간영역 등화기법을 제안한다. 제안된 기법이 주파수 옵셋이 있는 시변 다중경로 페이딩 환경에서 OFDM 시스템에 적합함을 컴퓨터 모의실험을 통해 확인한다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 1999.11b
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• pp.161-165
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• 1999

다중경로 채널의 시변 특성은 OFDM(orthogonal frequency division multiplexing) 신호의 직교성을 파괴시키며 이는 인접 채널간 간섭(ICI: inter channel interference)을 발생시켜 도플러 주파수에 비례하는 오류를 발생시킨다. 본 논문에서는 채널 시변의 원인을 주파수 옵셋과 도플러효과로 규정하고, 주파수 옵셋을 보정하기 위해 기존의 선형보간법(LI: linear interpolation method)대신 선형위상보간법(LPI: linear phase interpolation)과 도플러효과에 의한 ICI를 제거하기 위해 기존의 주파수영역 둥화기법보다 효과적인 시간영역 등화기법을 제안한다. 제안된 기법이 주파수 옵셋이 있는 시변다중경로 페이딩 환경에서 OFDM 시스템에 적합함을 컴퓨터 모의실험을 통해 확인한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.8C
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• pp.627-632
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• 2008

The timing offset is one of the main error sources in estimating the frequency offset in orthogonal frequency division multiplexing (OFDM) systems. Although some works have been done to mitigate the influence of the timing offset on the frequency offset estimation, most of the investigations require the knowledge of the timing offset range, which is not generally available in practical systems. In this paper, we propose a new frequency offset estimation scheme using differential combining between two successive correlation samples, which does not require the knowledge of the timing offset range, and thus, is robust to the timing offset variation. The simulation results show that the proposed scheme is not only robust to the timing offset variation, but also generally performs better than the conventional scheme on the average, in the case of the timing offset range being not known exactly.