• 한국위성정보통신학회논문지
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• 제3권2호
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• pp.48-53
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• 2008

In the future, satellite communication systems, such as ISDB in Japan and DVB in Europe, are required to support higher transmission date rate for providing multimedia services including HDTV, high rate data communication etc. Considering the effectiveness of OFDM technique in efficient usage of frequency bandwidth and its robustness to the multi-path fading, several OFDM based standards have been proposed for satellite communication. However, the problem of high Peak to Average Power Ratio is one of the main obstacles for the implementation of OFDM based system. Many PAPR reduction schemes have been proposed for OFDM systems. Among these, the partial transmit sequences (PTS) is attractive as they obtain better PAPR property by modifying OFDM signals without distortion. In this paper, considering the complexity issue, we present a simplified minimum maximum (minimax) criterion and Sub-Optimal PTS algorithm to optimize the phase factor. This algorithm can be dynamically made tradeoff`f between performance and complexity on demand. In addition, we integrate guided scrambling (GS) with this method. Simulation in multiple antenna based OFDM system proves that the proposed Hybrid schemes can get much more PAPR reduction and do not require transmission of side information (SI). Thus it is helpful when implementing OFDM technique in satellite communication system.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2004년도 전력전자학술대회 논문집(2)
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• pp.874-877
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• 2004

This paper presents the bus controller analysis of a power control unit of GEO satellite with 3kW power output. The sensing error of bus voltage produce control signal of the shunt switch assembly and the battery power converter, and the tolerance of error signal generated decide the stability of proposed system. The worst case analysis considered for the initial tolerance, temperature effect, tolerance of end of life is peformed to verify a designed bus controller. And also, the stability of system proposed according to moving of zero and pole values by some component failures is analyzed.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2009년도 공동학술대회
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• pp.368-371
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• 2009

전세계위성항법시스템(GNSS)의 하나로 EU에서 추진중인 GALILEO 프로젝트의 추진현황을 파악하였으며, 특히 최근에 발사되어 각종 신호를 시험하고 있는 GIOVE-A,B 실험위성의 다중경로 오차, 신호강도, 수신안테나 성능 및 L1-E5 신호지연에 대한 분석자료를 소개하였다. 그리고 EU의 GALILEO 프로젝트 진행 상황과 동향을 파악하여 국가적 대응 방향을 제안하고자 한다.

• 항공우주시스템공학회지
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• 제9권3호
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• pp.39-46
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• 2015

An integrated simulation program for an artificial satellite's operation has been developed. The program integrates and simulates orbit mechanics, attitude control, power/energy transition and mass variation. In the early stages of satellite development, this program can be used as a communication tool among design engineers of different fields. As a result, the efficiency to design a satellite is expected to increase. This program has been coded by Modelica language which supports acausal and object oriented programming methods. Libraries are developed for satellite simulation, and simulation results are presented.

• 한국군사과학기술학회지
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• 제21권6호
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• pp.826-841
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• 2018

The military satellite communication of ROK military, ANASIS is designed for analog data such as voice and streaming data. ANASIS cannot fully support ALL-IP communications due to its long propagation delay. The next generation satellite communication system is being designed to overcome the limitation. Next generation satellite communications system considers both high-speed and low-speed networks to support various operating environment. The low-speed satellite supports both broadband and narrow-band communication. This network works as the infrastructure for of wide-area internetworking over multiple AS's in the terrestrial network. It requires minimum satellite frequency and minimum power and works without PEP and router. In this paper, we propose a network operation structure to enable the inter-operation between high and low-speed satellite networks. In addition, we propose a data link protocol for low speed satellite networks.

• 한국위성정보통신학회논문지
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• 제2권2호
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• pp.69-74
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• 2007

최근 이동환경에서의 고속 위성통신 서비스에 대한 요구가 증가하고 있다. 이러한 요구를 만족시키기 위해 유럽 및 북미지역에서는 지난 수년간 Ku대역을 활용한 고속이동체 대상의 이동형 위성통신 시스템 개발이 활발히 진행되고 있다. 하지만 기존의 이동형 위성통신 시스템은 수십 Kbps 정도의 전송속도를 제공하기 때문에 고속열차와 같이 다수의 그룹 사용자들을 대상으로 한 위성 인터넷 서비스 제공에 한계가 있다. 또한, 철도 운행구간에서 발생하는 N-LOS 환경에 대처하는 기술의 부재로 서비스 가용도가 크게 저하된다. 본 논문에서는 고속열차 승객을 대상으로 위성무선연동 전송기술을 이용하여 지상무선망과 동일한 수준의 끊김없는 인터넷 서비스를 제공하기 위한 이동형 광대역 위성 인터넷 접속 시스템에 대해 기술한다. 고속열차를 대상으로 이러한 서비스 제공을 위해서는 터널이나 역사(Railway Station)와 같은 N-LOS 환경에 대한 대처기술이 필요하며, LOS 환경에서도 철로상에 설치되어 있는 Electric Power Post 나 Power Bridge 등으로 인한 주기적이고 짧은 시간 동안의 신호열화 현상이나 고속 이동에 따른 도플러 현상에 대한 극복기술이 필요하다. 이를 위해 본 시스템에서는 안테나 다이버시티 기법 및 갭필러와 지상무선망과의 연동기술이 적용되어야 하며, 상위 레이어에서의 에러 정정 기술이 적용된다. 본 논문에서는 위와 같은 기술이 적용되어 고속열차 승객들을 대상으로 한 위성인터넷 서비스 기술에 대해 기술한다.

• 한국항공우주학회지
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• 제36권4호
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• pp.384-392
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• 2008

위성의 전력계, 질량, 비용 등과 같은 형상 요소들의 개략적인 제원 도출은 본격적인 위성개발 전 반드시 수행되어야 할 중요한 과정이다. 본 논문에서는 최근 개발된 국내외 위성 개념설계 도구들의 주요한 특징들을 조사하고, 이를 바탕으로 초기 개념설계 절차를 정리하였다. 위성 개념설계는 탑재체와 임무에 근거하여 필요한 전력을 추정하고 위성운용에 필요한 태양전지판과 배터리와 같은 전력계를 추정한다. 다음으로 기존 위성들의 데이터베이스를 기반으로 탑재체질량에 따른 전체 위성 및 주요 서브시스템의 질량을 결정한다. 비용 역시 복잡한 계산 없이 기존 위성들의 데이터베이스를 바탕으로 대략적인 추정이 가능하다.

• 한국전산유체공학회지
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• 제10권2호
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• pp.48-53
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• 2005

This work discusses the numerical analysis, the design and experimental test of the SMA actuator along with its capabilities and limitations. Convective heating and cooling using water actuate the SMA(Shape memory alloy) element of the actuator. The fuel such as propane, having a high energy density, is used as the energy source for the SMA actuator in order to increase power and energy density of the system, and thus in order to obviate the need for electrical power supplies such as batteries. The system is composed of a pump, valves, bellows, a heater(burner), control unit and a displacement amplification device. The experimental test of the SMA actuator system results in 150 MPa stress(force : 1560 N) with $3\%$ strain and 0.5 Hz. actuation frequency. The actuation frequency is compared with the prediction obtained from numerical analysis. For the designed SMA actuator system, the results of numerical analysis were utilized in determining design parameters and operating conditions.

• Journal of Positioning, Navigation, and Timing
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• 제7권4호
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• pp.267-275
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• 2018

The reference stations in a satellite-based augmentation system (SBAS) collect raw data from global navigation satellite system (GNSS) to generate correction and integrity information. The multipath signals degrade GNSS raw data quality and have adverse effects on the SBAS performance. The currently operating SBASs (WAAS and EGNOS, etc.) survey existing commercial equipment to perform multipath assessment around the antennas. For the multi-path assessment, signal power of GNSS and multipath at the MEDLL receiver of NovAtel were estimated and the results were replicated by a ratio of signal power estimated at NovAtel Multipath Assessment Tool (MAT). However, the same experiment environment used in existing systems cannot be configured in reference stations in Korean augmentation satellite system (KASS) due to the discontinued model of MAT and MEDLL receivers used in the existing systems. This paper proposes a test environment for multipath assessment around the antennas in KASS Multipath Assessment Tool (K-MAT) for multipath assessment. K-MAT estimates a multipath error contained in the code pseudorange using linear combination between the measurements and replicates the results through polar plot and histogram for multipath assessment using the estimated values.

• 전기학회논문지
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• 제57권3호
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• pp.403-408
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• 2008

The gyroscope is the sensor for detecting the rotation in inertial reference frame and constitute the navigation system together an accelerometer. As the inertial reference equipment for attitude determination and control in the satellite, the mechanical gyroscope has been used but it bring the disturbance for mass unbalance so the disturbance give a bad influence to the observation satellite mission because the mechanical gyroscope has the rotation parts. During the launch. The mechanical gyroscope is weak in vibration, shock and has the defect of narrow operating temperature range so it need the special design in integration. Recently the low orbit observation satellite for seeking the high pointing accuracy of image camera payload accept the FOG(Fiber Optic Gyro) or RLG(Ring Laser Gyro) for the attitude determination and control. The Ring Laser Gyro makes use of the Sanac effect within a resonant ring cavity of a He-Ne laser and has more accuracy than the other gyros. It need the 1000V DC to create the He-Ne plasma in discharge tube. In this paper, the design process of the High Voltage Power Supply for RLG(Ring Laser Gyroscope) is described. The specification for High Voltage Power Supply (HVPS) is proposed. Also, The analysis of flyback converter topology is explained. The Design for the HVPS is composed of the inverter circuit, feedback control circuit, high frequency switching transformer design and voltage doubler circuit.