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      • Thermal Control Design for GEO Communication Satellite

        통신위성우주산업연구회 통신위성우주산업연구회 2006 Joint Conference on Satellite Communications Vol.2006 No.-

        통신해양기상위성은 항공우주연구원(KARI)이 개발하고 있는 통신, 해양 및 기상 관측 목적을 갖고 있는 정지궤도 위성이다. 남쪽 패널에는 Ka 밴드 통신 탑재체가, 북쪽 패널은 해양 및 기상 탑재체 관련 전자장비들이 부착되어 있다. 통신 탑재체의 열제어를 위해, 수동형 하드웨어와 함께 히터가 사용된다. 발열량이 많은 통신 장비들은 외장형 히트 파이프 위에 장착되며, 다층박막절연재(MLI)를 사용하여 위성의 다른 부분과 열적으로 분리시킨다. 위성의 외부 표면은 열의 방출 및 차단을 위해 방열판 및 다층박막 절연재등이 사용된다. 또한 부품의 작동온도에 따라 몇개의 영역으로 나누어 열제어를 수행하는 방법을 사용한다. 임무말 하지, 동지, 임무초 춘추분에 대하여 열제어계 검증을 위한 열해석이 수행되었다. 본 논문은 통신해양기상위성의 열제어의 기본적인 개념 및 그에 대한 열해석을 다루고 있다. COMS (Communication, Ocean and Meteorogical Satellite) is a geostationary satellite and has been developing by KARI for communication and ocean and meteorogicial observations. Ka-band components are installed on South wall, while other equipment for sensors are installed on the opposite side, North wall. A conventional thermal control design is baselined, using well established techniques and space proven hardware in a passive design, supplemented by heater to compensate environmental and unit dissipation variations. High dissipating communication units are located on external (surface) heat pipe and are covered by MLI (Multi Layer Insulation) to decouple them from the rest of the spacecraft. External spacecraft walls are covered by MLI or OSR (Optical Solar Reflector) for insulation from space and for rejection internal heat to space. The Ka-band payload section of south wall is divided several areas based on unit operating temperature in order to optimize radiator area and maximize heat rejection capability. Thermal analysis is carried out for validation of thermal control design. This paper presents principles of thermal control design and results of thermal analysis for COMS.

      • Hierarchical Modulation Scheme for Capacity Enhancement in the Satellite

        통신위성우주산업연구회 통신위성우주산업연구회 2006 Joint Conference on Satellite Communications Vol.2006 No.-

        이동통신을 비롯하여 많은 무선통신 시스템에서 사용자들의 멀티미디어 정보에 대한 수요가 증가함에 따라 채널의 용량을 늘리기 위한 여러 가지 방법들이 시도되고 있다. 그러나 현실적으로 여러 가지 제약에 의하여 사용할 수 있는 채널의 숫자와 용량이 제한되어 있다. 이러한 상황을 해결하여 좀 더 크고 많은 채널을 얻기 위한 여러 가지 방법들이 소개되었고 현재에도 연구되고 있다. 이 논문에서는 위성DMB 시스템을 기반으로 하여 제시된 여러 가지 방법 중 계층변조 방식을 이용하여 채널의 용량 및 그에 따른 성능을 분석하도록 한다. 특정 환경에서 사용자 수 증가에 의한 성능분석 및 계층변조 방식과 기존의 방법을 비교 분석하도록 한다. Future communication systems are to be designed to support and serve multimedia and multiple data transmission. Nowadays, requirement of mobile subscribers for the various information such as movie, GPS(Global Positioning System) information, news - is increasing significantly. However, due to practical reasons, the capacity and number of capable channels are limited. To solve this problem, a large number of methods and schemes have been proposed and are under research. In this paper, we demonstrate how satellite DMB (Digital Multimedia Broadcasting) system works with hierarchical modulation scheme. By using hierarchical modulation, we can analyze the capacity. Meanwhile, system performance is evaluated and compared to conventional 0MB system without using hierarchical modulation.

      • A New Switching Scheme Using Hadamard-Coded CDMA and Onboard Multiport Coupler for Multibeam Satellites

        Mahmud, Imam,Rahaman, Taifur,Wazedi, Al,Kawai, Kawai 통신위성우주산업연구회 2004 Joint Conference on Satellite Communications Vol.2004 No.-

        Satellite communications are the outcome of research in the area of communications in which the objective is to achieve ever increasing ranges and capacities with the lowest possible costs. With a conventional signal beam satellite the transmission capacity is limited due to its low antenna gain, so a multibeam satellite which can make the antenna gain much higher is prospective. In the multibeam system an onboard switching device is necessary to interconnect among beams. For example, the payload for SS-TDMA includes a programmable switch matrix having a number of inputs and outputs equal to the number of beams. This paper proposes a new alternative system for controlling the interconnection without onboard switch devices. This system uses Hadamard-coded CDMA as a multiple access scheme and a Multiport coupler onboard. Each earth station chooses the appropriate Hadamard code corresponding to the destination beam. The satellite which includes passive circuits using a multiport coupler autonomously controls the routing of the CDMA signals transmitted from earth stations. This system can be used effectively for sending signals from a source to a destination beam and reduces the controlling complexity. This paper presents a system model which can eliminate the onboard switching in the satellite and also the performance of the system.

      • 통신방송위성 시스템 개발

        이성팔,은종원,박종흥,Lee, Seong-Pal,Eun, Jong-Won,Park, Jong-Heung 통신위성우주산업연구회 2000 Joint Conference on Satellite Communications Vol.2000 No.-

        위성통신은 일반적으로 광대역폭을 사용하여 가장 경제적인 통신을 제공하는 수단으로 인식되고 있으며, 통신방송위성은 광 통신장비 설치에 많은 비용이 소요되어 통신을 제공하기 어려운 지역이나, 선박과 같은 이동체에 통신을 제공할 수 있는 가장 유용한 수단이 되고 있다. 한국전자통신연구원은 1990년 이래 정보통신부의 지원과 국가우주개발 중장기 계획에 의거하여 통신방송위성 및 관련 핵심기술에 대한 연구개발을 수행하여왔다. 본 논문은 위성 임무, 개발 방법, 범위, 전략, 일정, 그리고 탑재체 활용 전망 등 한국전자통신연구원이 주관하는 통신방송위성 시스템개발에 대하여 기술 한다. It is mainly recognized that satellite communications provide the economical communications solution because of their wide bandwidth. Moreover, communications and broadcasting satellite becomes a useful means in providing communications where it is too expensive to run a fiber or in mobile applications such as ships. ETRI has been working on research and development in communication and broadcasting satellite and its core technologies according to the national "mid and long-term space development" under the guidance of Ministry of Information and Communications since 1990. This paper focuses on ETRI's project of "communications and broadcasting satellite system development" which has been initiated, i.e., satellite mission, development methodology, scopes of development, development strategy, development schedule, and prospects of payload system utilization.

      • C and Ku Nands VSAT Antenna Designs for Intelsat Type Approval

        Lee, Don-Shin,Kim, Chang-Sik,Lee, Byung-Kap 통신위성우주산업연구회 2004 Joint Conference on Satellite Communications Vol.2004 No.-

        This paper presents a VSAT (Very Small Aperture Terminal) antenna design for Intelsat Type Approval at C and Ku bands. In general, most satellite owners want to perform their satellites without interference. Intelsat regulates some antenna parameters such as first sidelobe, cross polarization, axial ratio, envelope lines etc. for operating both up and down links. High Gain Antenna Company (HGA) has achieved to develop and to manufacture a 1.8m parabolic axi-symmetric offset reflector which is composed by SMC (Sheet Molding Compounds) with good RMS as well as a mesh screen imbedded. The C band RF feed is a wide band circular polarized system (3.625-6.425 GHz) meeting requirements. Also, the Ku-band (10.95-14.50 GHz) feed meets specifications for Type Approval. The paper describes the qualified reflector and feed system designs, RF bench test results and antenna radiation patterns with goof performance. Prior to the entrance of the world commercial market, HGA has tried to improve antenna performance for the CSAT application. In addition, mechanical support structure for pointing a satellite on axis is efficiently designed for low cost, lightweight, longer duration, etc. For convenience of installation, each component of the antenna system reduces number of pieces of parts and the antenna package includes a tooling set to mount a feed horn on the right focus point.

      • 입력추정필터 알고리즘을 적용한 정지궤도 위성의 실시간 궤도결정 기술

        김방엽,박봉규,이상철,Kim, Bang-Yeop,Park, Bong-Gyu,Lee, Sang-Cheol 통신위성우주산업연구회 2004 Joint Conference on Satellite Communications Vol.2004 No.-

        정지궤도 위성의 실시간 궤도 결정에 입력 추정 필터 알고리즘을 적용하는 방안을 연구하였다. 일반적으로 위성 운용에서는 실시간 궤도 결정을 위해 확정 칼만 필터를 주로 사용한다. 확장 칼만 필터는 일반적인 비선형 문제에 적당하고 구도 조정이 없는 상태의 정지궤도 위성의 궤도 결정에서는 좋은 성능을 발휘한다. 그러나 위성에 궤도 조정이 있게 되면 추정 오차가 커지는 단점이 있다. 입력 추정 필터 알고리즘은 주로 기동하는 목표물을 추정하는 미사일에 많이 사용되어왔다. 이 알고리즘은 목표물이 언제든지 불규칙한 기동을 할 수 있다고 가정하고 필터 뱅크를 구성한다. 이 필터 뱅크는 여러 개의 가능한 추정 값을 만들어 내고 그 결과들을 확장 칼만 필터 결과와 비교하여 최적의 상태 값으로 갱신되도록 한다. 본 논문에서는 확장 칼만 필터만을 사용한 경우와, 입력 추정 필터를 같이 사용한 경우를 시뮬레이션 하여 그 결과를 비교해보도록 한다. 이러한 과정을 통해, 특히 남북 위치추정 기동 시에 입력 추정필터가 추정 정밀도 향상에 기여할 것으로 기대한다. We examined the applying of Input Estimation Filter (IEF) algorithm to the real-time orbit determination for a geostationary satellite. Generally, the Extended Kalman Filter (EKF) algorithm has been used to the real-time orbit determination in satellite operation. The EKF algorithm is good for the general non-linear estimation problem and robust to the geostationary orbit determination during the non-maneuvering period. But when the orbital maneuvers were occurred, the ordinary EKF shows some large errors. The IEF algorithm has been used to the missile for the tracking of maneuvering target. This algorithm assumes that the target can shows irregular maneuvering motion any time and configures a bank of filters. The filters in the bank generate many possible estimated statuses and compare to the EKF solution, and the best estimated status were adapted and updated finally. In this power, we are going to show the simulation results of the real-time orbit estimation output using EKF only and with IEF algorithm. Through the comparing the results we could expect that IEF algorithm can increase the estimation accuracy especially when the north-south stationkeeping maneuver.

      • A New Stabilization Technique for Microwave Waveguide Power Amplifier Modules

        Park, H.J.,Kim, M.,Chang, Y.K. 통신위성우주산업연구회 2004 Joint Conference on Satellite Communications Vol.2004 No.-

        Many attempts have been made to replace vacuum tube transmitters with solid state power amplifiers to produce watt-level output power required in millimeter-wave satellite communication system. In one case, the use of standard rectangular waveguide to combine powers from many medium size microstrip solid state amplifiers was investigated. Each microstrip amplifier used in the PA module was attached to the input and output tapered-slot antennas to couple powers from and into the waveguide. The completed module contained several microstrip amplifiers inserted in parallel inside the waveguide, and one such component built using an X-band waveguide demonstrated more than 40 Watts of output power [1]. These waveguide power amplifier modules, however, could suffer from oscillations because of the strong coupling between individual microstrip amplifiers. In other to increase amplifier stability and the isolation among amplifier elements, we propose a technique similar to the one used in Wilkinson power divider. Our X-band simulated model used two amplifier elements with their tapered-slot antennas tied together using a 130${\textohm}$ resistor. With a proper antenna design and a careful selection of the location for the stabilizing resistor, HFSS simulations showed reduced coupling between two amplifier elements from-6 to below-15dB across the full waveguide bandwidth. The proposed stabilizing circuitry had almost no effect on the amplifier gain and power and made the PA module more resistant to the failures of individual elements.

      • A Novel Spread Spectrum Communication System for LEO Satellite

        Ko, Sung-Hwan,Kang, Suk-Jin,Chang, Young-Keun 통신위성우주산업연구회 2004 Joint Conference on Satellite Communications Vol.2004 No.-

        위성통신의 발달은 지상의 통신 기술의 발달과 함께 이루어져 왔다. 향상된 지상의 통신기술을 위성에 적용하여 향상된 위성통신을 구현하는 것이 본 논문의 목표이다. 또한 저궤도 소형위성은 소비 전력에 상당히 민감하므로 효과적인 전력 제어를 통한 소비전력의 감소도 중요한 문제이다. 따라서 새로운 전력제어 기법을 통하여 위성통신의 신뢰성을 향상시킬 수 있는 방법과 이미 잘 알려져 있는 이동통신 기술인 주파수 확산 방식을 위성통신에 적용하여 소형위성의 통신 시스템의 신뢰성을 높이는 방안을 제안하고자 한다. 주파수 확산기술을 이용하여 물체를 구별하는 방법으로 확산 코드(PN code)인 Walsh 코드를 사용한다. 본 논문에서는 확산코드의 발생 방법과 변복조 방법에 대해 알아보고, 응답형 통신의 운용을 통해 저궤도 소형위성의 소비전력을 감소하면서 신뢰성 있는 통신을 가능케 하는 방법에 대해 알아보기로 한다. Communication technology of satellite has been developing with the advancement of terrestrial communication technology. The purpose of this paper is to apply an advanced terrestrial technology to satellite communication. Because LEO small satellite are very sensitive to power budget, reducing power consumption of satellites through effective power control is important. Therefore this paper will introduce methods for improving communication reliability through a novel power control technique and through a well-known spread spectrum used by mobile communication industry. An object distinction method described in this paper uses frequency spread spectrum technique with a Walsh code as its spread code(PN code). This paper will examine generation a method of spread code, a method of modulation and demodulation, and a possible method to a reliable communication while reducing power consumption of LEO small satellites.

      • A Class of Multiuser Interference Free Modulations Produced by General Orthogonal Modulations

        Yasunaga, Takashi,Oka, Ikuo,Ata, Shingo,Fujiwara, Chikato 통신위성우주산업연구회 2004 Joint Conference on Satellite Communications Vol.2004 No.-

        Suppression of multiuser interference effects in a frequency-selective fading channel is big issue in mobile communication system. In this paper, a parameter of modulations is discussed to develop new modulations which do not yield multiuser interference in CDMA. The modulations are shown to be in a certain class of general orthogonal modulations. The general orthogonal modulations are based on orthogonal vectors, which are obtained by multidimensional rotations and have parameters of rotation planes and rotation angles. We find the parameters of general orthogonal modulations that preserves orthogonality among users in the frequency-selective channel. The derived parameters express the new modulations, whose transfer matrices are expressed by a Kronecker product of two rotation matrices. We obtain the parameters that maximize constellation distance by computer simulations. Numerical results of distance are demonstrated to compare the performance of widely used CDMA and the new modulations proposed in this paper.

      • BBISS(Broad Band Internet Service via Satellite)Ka-band Broadband Satellite Plan

        Tatsukawa, Kenichi,Akinaga, Wakoto,Yamada, Kenichi,Hashimoto, Katsumasa,Okui, Tamio,Koishi, Yoichi,Horiuch, Yasuo 통신위성우주산업연구회 2004 Joint Conference on Satellite Communications Vol.2004 No.-

        Broadband internet, by ADSL, fiber optic, and CATV circuit has become very popular. However this service can not be shared in the depopulated area, where Broadband service business is difficult to materialize. BBISS satellite has been planned to provide the Broadband service to these un-equipped areas. In order to do so, a wide Ka frequency band is utilized and moreover, multi-beam antenna is adopted to realize the improvement of the efficient frequency reuse and to succeed in earth station antenna miniaturization. As for the problematic matter in use of the Ka-band due to great rainfall attenuation will be solved by use of adaptive code modulation method and realize high availability, and high=speed information speed will be provided in case of fine weather by maintaining the necessary minimum margin. This paper introduces best effort service by BBISS with such features.

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