• Proceedings of the KIPE Conference
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• 2020.08a
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• pp.344-345
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• 2020

본 논문에서는 계통연계형 시스템에서 계통 주파수 변동이 발생할 경우 계통 전류 왜곡 보상을 위한 주파수 적응형 위상기반 반복제어기의 설계기법에 대하여 기술한다. 기존의 반복제어기를 적용한 경우 계통 주파수 변동 시 주파수 변동에 따라 제어 성능이 보장되지 않는다는 단점이 있다. 이를 보완하기 위해 PLL로 추정된 계통 위상각을 이용한 반복제어기의 메모리 할당을 통해, 주파수 변동에 대응이 기능한 위성 기반 반복제어기의 설계 방법을 제안하였으며, 모의실험을 통해 그 성능을 검증하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.7A
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• pp.627-634
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• 2011

In this paper, a new frequency offset estimation method in OFDM system is suggested. To measure fractional part of frequency offset, the repetition feature of cyclic prefix and that of training sequence is adopted. Both method shows relatively large frequency offset estimation error under low SNR circumstances, but this error can be greatly reduced by joint measurement of cyclic prefix and inversely repeated training symbol such as primary advanced preamble (PA-preamble) of IEEE 802.16m IMT-Advanced WiMax system. In this paper, the performance of suggested frequency offset estimation method is verified in IEEE 802.16m IMT Advanced WiMax system, using its PA-preamble and cyclic prefixes of A-preambles.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.172-173
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• 2011

전력시스템 주파수는 주파수 계전기용도 이외에 전력시스템에 대용량 집중전원 및 소규모 분산전원이 연계될 때 동기 검정 계전기와 발전기 및 소내 변압기의 과여자 상태를 감지하는 V/F 계전기에서도 사용된다. 주파수 계측장치는 주파수 및 주파수 편이를 실시간으로 정확하고 신속하게 측정함으로서 정규 주파수를 유지시키고 더 나아가 사고파급방지에 대한 책무를 수행해야 한다. DFT필터는 광범위하게 사용되었으나 주파수가 편이하게 되면 오차가 발생된다. 근래 웨이브릿 변환이 새로운 주목을 받고 것은 지속적인 연구 결과, 단일 반복 방정식 형태로 연산 부담이 적어 실시간 신호 처리에 적당한 고속 반복 이산 웨이브릿 변환이 제시되었기 때문으로 생각된다. 본 논문에서는 FRDWT에 의한 주파수 추정 기법을 제시하고자 한다. 제시된 기법의 성능 평가는 발전기 내부사고와 외부사고 데이터에 의해 이루어졌다.

• Journal of the Korean Institute of Intelligent Systems
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• v.15 no.2
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• pp.135-142
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• 2005

This paper presents an adaptive repetitive control scheme for optical disk drives to track a variable periodic reference signal. Periodic disturbances can be adequately attenuated using the concept of repetitive control, provided the period is known. Because optical disk drives support various speeds, they have the varying periodic disturbances. Based on repetitive control to change sampling frequency to follow the change of reference period, an adaptive repetitive control is proposed in order to deal with such disturbances. The proposed control consists of the repetitive controller and the frequency generator. The former uses a varying sampler operating at fixed multiple times of the disturbance frequency and the latter generates the changeable sampling frequency based on the disturbance frequency. The experimental results on the control of an optical disk drive demonstrate the effectiveness of the proposed schemes and the improvement of random access time as well.

• Journal of Korea Society of Industrial Information Systems
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• v.12 no.4
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• pp.126-130
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• 2007

This paper presents a method to design a repetitive controller that is specified in the specified trajectory for the repetitive works. With the single-model design approach, the controller is derived by minimizing a frequency-domain based cost function that produces monotonic convergence of the tracking error as a function of repetition number. Numerical illustrations show how the proposed single-model design method produces a repetitive controller in a single nominal model of the system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.9C
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• pp.896-905
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• 2009

In this paper, we propose an enhanced iterative ICI (Inter Carrier Interference) cancellation method for cooperative STBC-OFDM (Space Time Block Coded-Orthogonal Frequency Division Multiplexing) system. In cooperative STBC-OFDM system, ICI cancellation is necessary because ICI due to the independent local oscillators always exits. The conventional iterative ICI cancellation method has severe performance degradation due to the initial estimation error. Also the performance degradation increases as CFOs (Carrier Frequency Offsets) and modulation order increases. Therefore, in this paper, we propose an enhanced iterative ICI cancellation method which can reduce the initial estimation error by giving a priority to initial estimation and cancellation process. Through the complexity and performance comparisons, we verwey that the proposed method has better performance with approximately same complexity compared with the conventional method.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.11
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• pp.1434-1442
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• 2019

In this paper, the channel change was continuously measured for 24 hours from July 5, 2017 on the coast near Deokjeok-do, Incheon. The underwater channel has various channel environment characteristics as the change in the time axis and the change in the frequency axis occurs in real time, and the underwater communication performance decreases due to the multipath fading and the Doppler effect. Therefore, in this study, we performed the OFDM system performance analysis in the underwater channel environment by applying the repetitive transmission diversity scheme in the time and frequency domain to improve the communication performance in the real-world underwater communication environment. Using the collected data, we compared the channel environment in the time and frequency domain and analyzed the BER performance according to the pilot spacing and the number of repetitive transmissions in the time and frequency axis.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.11
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• pp.1653-1660
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• 2016

The synthetic aperture rardar (SAR) is an active sensor using microwaves. It transmits a microwave signal, called a chirp pulse, and receives the reflected signal in a moving platform such as satellite and unmanned aerial vehicle. Since this sensor uses microwaves that can penetrate the atmosphere, SAR generates the images regardless of light and weather conditions. However SAR operates on the moving platform, the Doppler shift and the side-looking observation method should be considered. In addtion, a residual image or ghost image can be occurred according to selection of the pulse repetition frequency (PRF). In this paper, a range design of the PRF for the L-band spaceborne SAR system is studied for prevention of SAR image distortion. And the system is studied for prevention of SAR image distortion. And the system parameter and the PRF are calibrated iteratively according to the proposed system design procedure and design constraints. The MATLAB based on SAR system simulator has been developed to verify the validity of calculated PRF. The developed simulator assumes that SAR sensor is operated by the PRF calculated from the design. The results of the simulator show that the targets in image has a valid peak to side-lobe ratio (PSLR) so that the PRF can be used for the spaceborne SAR sensor.

• Journal of Korea Water Resources Association
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• v.44 no.9
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• pp.731-740
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• 2011

An acoustic velocity profiler is developed, which is able to be used for open-channel flow measurement. It measures flow velocity based Doppler effect on acoustic signals, which is estimated by using pulse repetition frequency technique. Laboratory and field tests were made to verify velocity measuring performance of the developed device. It is confirmed that the acoustic velocity profiler can normally measure vertical velocity profile in the range above 0.1 m from the bottom and has equivalent performance to commercial acoustic velocity measuring devices.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2016.06a
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• pp.297-299
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• 2016

본 논문에서는 ATSC 3.0 규격에서 정의되는 부트스트랩 신호를 이용한 수신기 동기 방식에 대해서 소개한다. ATSC 3.0 방송 신호의 프레임에 앞서서 전송되는 부트스트랩 신호는 시간영역에서 반복되는 구조를 가지므로 이를 이용하여 수신기에서 타이밍 및 주파수 동기를 획득할 수 있다. 본 논문에서는 부트스트랩 신호의 시간영역의 반복구조를 이용하여 수신기에서 타이밍 및 주파수 동기 획득 방법을 제시한다.