• Journal of Astronomy and Space Sciences
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• 제37권2호
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• pp.105-115
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• 2020

The Korean Institute of Technology Satellite (KITSAT-1) is the first satellite developed by the Satellite Technology Research Center and the University of Surrey. KITSAT-1 is orbiting the Earth's orbit as space debris with a 1,320 km altitude after the planned mission. Due to its relatively small size and altitude, tracking the KITSAT-1 was a difficult task. In this research, we analyzed the tracking results of KITSAT-1 for one year using the Midland Space Radar (MSR) in Texas and the Poker Flat Incoherent Scatter Radar (PFISR) in Alaska operated by LeoLabs, Inc. The tracking results were analyzed on a weekly basis for MSR and PFISR. The observation was conducted by using both stations at an average frequency of 10 times per week. The overall corrected range measurements for MSR and PFISR by LeoLabs were under 50 m and 25 m, respectively. The ionospheric delay, the dominant error source, was confirmed with the International Reference of Ionosphere-16 model and Global Navigation Satellite System data. The weekly basis orbit determination results were compared with two-line element data. The comparison results were used to confirm the orbital consistency of the estimated orbits.

• 한국통신학회논문지
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• 제24권6A호
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• pp.871-880
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• 1999

본 논문은 광대역 CDMA 방식의 IMT-2000 단말기용 이동국의 PN 코드 위상 동기를 위한 추적기와 데이터를 복원하는 복조기회로 설계 및 구현에 대해서 기술한다. 먼저 동기 추적을 위한 회로는 넌코히어런트 방식을 사용하여 설계하였으며 동기 추적 과정에서 발생되는 클럭이 1/8 PN 칩의 해상도를 갖도록 설계하였다. 복조기 부분은 코히어런트 방식을 사용하여 설계하였으며 타임 트래킹 동작에 의해서 발생되는 클럭으로 생성된 PN 코드와 수신신호를 역확산하여 원래의 데이터를 복원하도록 설계하였다. 32.786 MHz의 구동 클럭과 4.096 MHz의 칩율을 사용하였으며 FPGA로 구현하였다. 또한 설계된 복조기는 32Kbps 음성 및 신호 채널에서 정상 동작함을 확인하였다. 성능 검증을 위하여 AWGN(Additive White Gaussian Noise) 7dB로 시뮬레이션하여 데이터 복원이 이루어 졌으며 무선 가입자망(WLL:wireless local loop)과 IMP-2000 변복조기 설계에 적용할 수 있음을 알 수 있었다.

• 한국통신학회논문지
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• 제34권3C호
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• pp.329-340
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• 2009

본 논문에서는 이진천이반송파 (binary offset carrier, BOC) 변조된 확산신호의 부호동기추적에 적합한 기법을 제안한다. 이진천이반송파 변조된 확산신호의 상관함수는 정확한 상관옵셋에서 나타나는 주첨두와 여러 부첨두를 갖고 있다. 다중 경로 채널환경에서 가시신호에 비해 다중경로신호는 항상 지연되어 수신되기 때문에 여러 부침두 가운데 정확한 상관옵셋보다 이른 상관옵셋 영역에 있는 상관함수는 늦은 상관옵셋영역에 있는 상관함수에 비해 덜 왜곡된다. 본 논문에서는 이 특징을 활용해 BOC(n,n) 변조된 확산신호의 부호추적에 적합한 이른영역상관(advanced region correlation, ARC) 기법을 제안한다. 그리고 모의실험을 통해 안정된 다중경로 (static multipath) 채널과 지상이동체위성시스템 (land mobile satellite system) 채널에서 기존과 제안한 기법의 부호동기 추적성능을 비교한다. 또한 BOC(pn,n) 변조된 확산신호에 적합한 이른영역상관 기법의 확장 형태인 일반화된 이른영역상관기법 (generalized-ARC, G-ARC) 제안하고, 모의실험을 통해 그 성능을 보인다.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제14권4호
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• pp.295-304
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• 2014

Communication infrastructure supports wide variety of mobile services such as photo and file sharing, location tracking, social network services and instant messaging. However, instances like power-loss and natural disasters disrupt these communication infrastructures unable to render support to these mobile services. Delay-tolerant networks (DTNs) offer a solution to these problems at hand. By utilizing mobility and opportunistic contacts among mobile devices, a plausible communication network can be establish and enable support to mobile applications. This paper presents an energy-efficient, reliable message delivery routing scheme with message prioritization rules for DTN. It uses the context information of nodes (mobile devices) such as the contact history (location and time of contact), speed/velocity, moving direction to determine the best forwarders among nodes in the network. The remaining energy of the nodes is also used to determine the message types a node can deliver successfully. The simulation results show that proposed approach outperforms Epidemic and Prophet routing schemes in terms of delivery ratio, overhead ratio, delivered messages per types and remaining energy.

• International Journal of Railway
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• 제4권4호
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• pp.93-96
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• 2011

The basic element of the EMS suspension is the electromagnet system, which suspends the vehicle without contact by attracting forces to the rails at the guideway. The suspension of a vehicle by attractive magnetic forces is inherently unstable and consequently it is continuously adjusted by the strength of the suspending electromagnet from rail irregularity and bending of the guideway. In order to improve reliable tracking, it needs to get feedback signals without measurement delay time. In this paper the concept of feedback control system with Kalman Filter in EMS is proposed. The input signals in the feedback control system are an air-gap and an acceleration signal. The air-gap signal with noise from the gap sensor is transformed to the filtered air-gap signal y without measurement delay time by using Kalman Filter. The filtered air-gap signal is transformed to a relative velocity and a relative acceleration signal. Then it multiplies these values by gain matrix in order to get the actuator's reference voltage value. The simulation results show that the dynamic responses of the suspension system can be improved by reducing the influence of measurement delay time of air-gap signals.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1998년도 학술발표대회 논문집 제17권 1호
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• pp.499-502
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• 1998

본 논문에서는 한 쌍의 수동소나를 이용하여 미지의 잠항물체의 존재 유무를 확인하고 각 센서에 도달하는 시간지연의 차를 평가하는 Detection과 Tracking 알고리즘을 연구한다. 이 과정에서 이동하는 표적의 속력에 의한 도플러효과를 보상하는 2차원 확률분포 함수를 적용함으로 보다 정확한 결과를 도출한다. 관측신호의 Cross-Correlation과 Bayesian Method를 이용하여 계산한 시간지연과 도플러효과 비의 이차원 Likelihood 함수로부터 사후확률 (Posterior Probability)을 구하여 발견 평가와 추적을 수행한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1993년도 정기총회 및 추계학술대회 논문집 학회본부
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• pp.293-295
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• 1993

In this paper, Neural-Network Identifier that has time-delay element, error limit and small weighting factor is proposed. A proposed identifier has good performance to identify non-linear system with noise. To test the effectiveness of the algorithm presented above, the simulation for output tracking of non-linear system is implemented.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1995년도 Proceedings of the Korea Automation Control Conference, 10th (KACC); Seoul, Korea; 23-25 Oct. 1995
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• pp.496-499
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• 1995

In this paper, a new detection scheme, the detectable maneuver set (DMS) scheme, is proposed by incorporating the trade-off property between target maneuver magnitude and detection time delay. With this new detection scheme, small maneuvers can be effectively detected without enlarging window size. Simulation results show that the proposed DMS scheme gives better tracking performance.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1987년도 한국자동제어학술회의논문집; 한국과학기술대학, 충남; 16-17 Oct. 1987
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• pp.135-138
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• 1987

A method for designing a robust tracking controller for linear discrete systems is investigated. Only the observable variables are to be used in the controller synthesis. To insure the robustness, the system is augmented by a compensator at the output side. Then a feedback controller is designed using delayed values of the observable variables for the augmented system. The delay times are chosen to minimize the effect of measurement accuracy and/or noise.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.998-998
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• 2008

It is difficult to find for analysis solution of the synchronous generator exciter system. Recently, it had good performance UPS converter system using CRA method. The single converter of synchronous generator excitor system under considerations : (i) the overall system shall keep very low AC-voltage tracking error as well as no phase delay over different load condition, and (ii) the digital controller shall be employed at a fixed sampling. It is shown that the synchronous exciter system can be achieved by the proposed controller using Characteristic Ratio Assignment.