• 한국정보전자통신기술학회논문지
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• 제3권1호
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• pp.31-37
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• 2010

본 논문에서는 직교 주파수 분할 다중 (orthogonal frequency division multiplexing: OFDM) 기반 지상파 디지털 비디오 방송 (digital video broadcasting-terrestrial: DVB-T) 시스템에서 파일럿을 이용하여 정수 주파수 옵셋을 (integer frequency offset: IFO) 추정하는 새로운 기법을 제안한다. 기존 기법은 IFO를 추정하는데 사용되는 파일럿의 채널응답이 빠르게 변한다는 가정 하에, 파일럿이 제공하는 조합 정보 중 일부분만 이용하여 IFO를 추정한다. 본 논문에서는 IFO 추정 성능을 향상 시킬 수 있도록 파일럿이 제공하는 부가적인 조합 정보를 이용하여 IFO를 추정하는 효율적인 기법을 제안한다. 모의실험을 통해 제안한 기법의 IFO 추정 성능이 기존 기법보다 뛰어남을 확인할 수 있다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 학술대회 논문집 전문대학교육위원
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• pp.80-85
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• 2001

Frequency is an important operating parameter of a power system. Frequency of a power system remains constant if sum of all the loads plus losses equals total generation in the system. However, the frequency starts to decrease if total generation is less than the sum of loads and tosses. On the other hand, the system frequency increases if total generation exceeds the sum of loads and losses. Electric power systems sustain transient frequency swings whenever the balance between generation and load does not no longer hold. To cope with this Constraints, it requires an accurate and high speedy frequency deviation estimation technique and suitable adjustment to obtain the power system energy balance. The fundamental frequency component of 3-phase signal is first extracted by using an algorithm based on FIR(finite duration impulse response) filter, a phase angle of a voltage. The rate change of the phase angle is used for estimation and speed in its process. Also, to confirm the validity of the proposed algorithm, the simulation results obtained by using EMTP(electro magnetic transients program) are shown.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2008년도 정보통신설비 학술대회
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• pp.437-440
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• 2008

In this paper, we present and analyze a robust frequency offset estimation scheme for orthogonal frequency division multiplexing (OFDM) systems over radio communication channels. When there exists frequency offset, the loss of orthogonality occurs and the interference problem among several subcarriers in OFDM signals is introduced. The guard interval of OFDM signals is employed for estimating the frequency offset. Furthermore, in order to enhance the frequency offset estimation performance, a ternary sequence is utilized. A frequency offset is estimated based on the synchronized correlator output. The proposed frequency offset estimation scheme can be applied to track the carrier frequency offset of OFDM systems.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 학술대회 논문집 정보 및 제어부문
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• pp.277-279
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• 2004

In this paper, we propose an channel estimation method for Multi-Input Multi-Output-Orthogonal frequency Division Multiplexing (MIMO-OFDM). The proposed method estimates uniquely all channel frequency responses needed in space-frequency block coded OFDM systems using "comb-type" pilot symbols. To reduce the computational complexity of the proposed method, least square(LS) and linear minimum mean square error(LMMSE) are used in the frequency-domain. The performance of the proposed approach is evaluated by computer simulation for rayleigh fading channel.

• Journal of Power Electronics
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• 제16권3호
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• pp.1067-1075
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• 2016

This paper presents an adaptive observer-based approach to estimate voltage parameters, including frequency, amplitude, and phase angle, for single-phase power systems. In contrast to most existing estimation methods of grid voltage parameters, in this study, grid voltage is treated as a dynamic system related to an unknown grid frequency. Based on adaptive observer theory, a full-order adaptive observer is proposed to estimate voltage parameters. A Lyapunov function-based argument is employed to ensure that the proposed estimation method of voltage parameters has zero steady-state error, even when frequency varies or phase angle jumps significantly. Meanwhile, a reduced-order adaptive observer is designed as the simplified version of the proposed full-order observer. Compared with the frequency-adaptive virtual flux estimation, the proposed adaptive observers exhibit better dynamic response to track the actual grid voltage frequency, amplitude, and phase angle. Simulations and experiments have been conducted to validate the effectiveness of the proposed observers.

• Journal of Communications and Networks
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• 제9권4호
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• pp.466-472
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• 2007

Single carrier block transmission with frequency domain equalization(SC-FDE) has been shown to be a promising candidate in ultra-wideband(UWB) communications. In this paper, we analyze the performance of SC-FDE over UWB communications with channel estimation error. The probability density functions of the frequency domain minimum mean-squared error(MMSE) equalizer taps are derived in closed form. The error probabilities of single carrier block transmission with frequency domain MMSE equalization under imperfect channel estimation are presented and evaluated numerically. Compared with the simulation results, our semi-analytical analysis yields fairly accurate bit error rate performance, thus validating the use of the Gaussian approximation method in the performance analysis of the SC-FDE system with channel estimation error.

• 전력전자학회논문지
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• 제23권2호
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• pp.139-146
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• 2018

This work puts forward a theoretical analysis on position estimation performance of interior permanent magnet synchronous motor (IPMSM) according to the injection frequency in carrier-based sensorless operation. The effects of spatial harmonics on inductance and voltage distortion due to the nonideal characteristics of IPMSM and inverter are examined as factors influencing the position estimation performance. Furthermore, the position estimation performance is analyzed by calculating the current at the switching instant in several operating conditions. In summary, the half switching frequency injection is more robust to the nonideal characteristics of IPMSM, especially with light load condition. The validity of the analysis is verified by the simulation and experimental results.

• ETRI Journal
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• 제33권1호
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• pp.27-31
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• 2011

This paper addresses estimating the frequency of a cisoid in the presence of white Gaussian noise, which has numerous applications in communications, radar, sonar, and instrumentation and measurement. Due to the nonlinear nature of the frequency estimation problem, there is threshold effect, that is, large error estimates or outliers will occur at sufficiently low signal-to-noise ratio (SNR) conditions. Utilizing the ideas of averaging to increase SNR and weighted linear prediction, an optimal frequency estimator with smaller threshold SNR is developed. Computer simulations are included to compare its mean square error performance with that of the maximum likelihood (ML) estimator, improved weighted phase averager, generalized weighted linear predictor, and single weighted sample correlator as well as Cramer-Rao lower bound. In particular, with smaller computational requirement, the proposed estimator can achieve the same threshold and estimation performance of the ML method.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.197-198
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• 2008

Even if the DFT calculation is one of the general method to do phasor estimation, it can't adapt to alteration of the frequency. The Frequency is fastened to 60Hz in the ideal power system. However the frequency is not constant in real power system and fluctuates more followed by conditions of the power system. In these cases, the accurate phasor estimation is impossible by using a common DFT calculation, so that a frequency - adaptive phasor estimation method based on the fourier transform is proposed in this paper.

• ETRI Journal
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• 제34권3호
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• pp.458-461
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• 2012

In this letter, we propose a novel frequency offset estimation algorithm for space-time block code (STBC) orthogonal frequency division multiplexing systems. The algorithm mainly exploits the specific construction of STBC so that it does not need any additional pilots or sequences in the data field. The estimator is derived on the basis of the maximum likelihood theory. Simulation results show that this method can provide a significant performance improvement in terms of the estimation accuracy of the frequency offset.