• Journal of Positioning, Navigation, and Timing
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• 제1권1호
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• pp.45-49
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• 2012

The flight performance evaluation of navigation system is very significant because the reliability of navigation data directly affect the safety of aircraft. Especially, the high-level navigation system such as DGPS/INS, need more precise flight performance evaluation method. The performance analysis is evaluated by comparing between the navigation system in aircraft and reference trajectory which is more precise than navigation system in aircraft. In order to verify DGPS/INS performance of m-level, the GPS receiver, which is capable post-processed Carrier-phase Differential GPS(CDGPS) method of cm-level, have to be used as reference system. The DGPS/INS is estimated the Center of Gravity (CG) point of aircraft to offer precise performance while the reference system is output the position of GPS antenna which is mounted on the outside of aircraft. Therefore, in order to more precise performance evaluation, it needs to compensate the lever arm and coordinates transformation. This paper use quaternion and Direct Cosine Matrix(DCM) methods as coordinate transformation matrix in lever arm compensation of CDGPS reference trajectory. And it compares NED errors of DCM and quaternion transformation in lever arm of reference trajectory via DGPS/INS result.

• Journal of Astronomy and Space Sciences
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• 제33권1호
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• pp.45-54
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• 2016

This study developed an approach for improving Carrier-phase Differential Global Positioning System (CDGPS) based realtime satellite relative navigation by applying laser baseline measurement data. The robustness against the space operational environment was considered, and a Synthetic Wavelength Interferometer (SWI) algorithm based on a femtosecond laser measurement model was developed. The phase differences between two laser wavelengths were combined to measure precise distance. Generated laser data were used to improve estimation accuracy for the float ambiguity of CDGPS data. Relative navigation simulations in real-time were performed using the extended Kalman filter algorithm. The GPS and laser-combined relative navigation accuracy was compared with GPS-only relative navigation solutions to determine the impact of laser data on relative navigation. In numerical simulations, the success rate of integer ambiguity resolution increased when laser data was added to GPS data. The relative navigational errors also improved five-fold and two-fold, relative to the GPS-only error, for 250 m and 5 km initial relative distances, respectively. The methodology developed in this study is suitable for application to future satellite formation-flying missions.

• 정보과학회 컴퓨팅의 실제 논문지
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• 제21권12호
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• pp.798-803
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• 2015

DGPS는 기존 GPS의 위치측위 정밀도를 지상 기준국의 보정정보를 이용하여 향상시킬 수 있는 기술이다. 현재 전국을 대상으로 DGPS 보정정보 송출이 가능하도록 인프라가 구축되어 있으나, 고가의 DGPS 전용장비가 필요하다는 제약으로 제한된 분야에서만 활용되고 있다. 스마트폰을 이용한 DGPS 단말의 개발은 이러한 한계를 극복하고 다양한 위치기반 서비스에 DGPS를 적용할 수 있도록 함으로써, 위치기반 서비스의 새로운 서비스 모델의 구현이 가능하게 할 수 있다. 본 논문에서는 스마트폰 환경에서 DMB 방송망, 이동통신망을 통해서 수신된 DGPS 보정정보를 활용하여 고정밀 위치측위가 가능한 DGPS 단말 개발에 대해서 소개하고자 한다.

• 한국정보통신학회논문지
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• 제6권8호
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• pp.1175-1180
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• 2002

본 논문은 DARC 정보를 수신하여 실시간 정보와 사용자 정보를 표시하는 전광판을 차량용에 사용할 수 있도록 GPS모듈을 연결하여 위치 기반 정보를 표시할 수 있는 전광판을 구현하였다. GPS는 DARC모듈로부터 DGPS 정보를 수신하여 값의 정확성을 높이고 이러한 GPS 정보를 사용하여 위치 기반의 정보를 음성 및 전광판에 표시할 수 있게 했다. 본 시스템은 실험을 통해 사용자 메시지 및 DARC 정보 데이터와 정류장을 순서대로 표시하는 것을 확인하였다. 이는 대중 교통 수단에서 승객들에게 유용한 정보를 사용자 정보와 함께 제공함으로써 전광판의 효율을 높일 수 있게 된다.

• 제어로봇시스템학회논문지
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• 제8권5호
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• pp.425-433
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• 2002

After the removal of SA (Selective Availability), horizontal accuracy of 25m(2dRMS) is easily obtained using GPS (Global Positioning System). In this paper, the error characteristics without SA are analyzed and a navigation algorithm concerns this error characteristics is proposed to further improve the accuracy. The proposed method utilizes the relationship between elevation angle and errors that are remained after ionospheric and troposheric delay compensation. The relationship is derived from real measurements and used as a weighting matrix of weighted least squares estimator. Furthermore, a RAIM (Receiver Autonomous Integrity Monitoring) technique is included to remove abnormal measurements affected by multi-path or low SNR (Signal-to-Noise Ratio). It is shown that using the proposed method, more than 4 times accurate result, which is comparable with DGPS (Differential GPS), can be obtained from experiments with real data. Besides accuracy and reliability, the proposed method reduces large jumps in position and maintains better performance than a method using mask angle to completely remove satellites below this mask angle. Thus it is expected that the proposed method can be efficiently applied to land navigation where some satellites are blocked by building or forest.

• 한국정밀공학회지
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• 제25권12호
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• pp.132-138
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• 2008

Recently, mastering processes for high density optical disc such as Blu-ray disc rely on electron beams, which are operable in only vacuum. In the mastering process, one of the most important tasks is to design precision stages for providing precise positioning of the works with respect to the source in a high vacuum environment. In this paper, we have developed a precision rotation table usable in the electron beam mastering. The rotation table adopted air bearings for a high positioning repeatability and velocity stability. The air leakage from the air bearings has been minimized by employing the differential exhaust scheme using three steps of air drain. The design parameters such as diameters of exhaust lines, seal lengths, and pumping speeds were decided according to the optimization method using genetic algorithm. The performance on the vacuum level of the rotation table was evaluated experimentally and theoretically. The results indicate that a vacuum level of $10^{-4}$ Pa is achieved with operation of air bearings in a vacuum chamber, which is sufficient for the electron beam mastering.

• 대한공간정보학회지
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• 제19권3호
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• pp.75-82
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• 2011

본 연구에서는 기존 위성항법시스템의 경우 고가의 장비보유, 통신장애에 따른 이용의 제한 등의 단점을 보완할 수 있는 광역보정위성항법시스템인 위성기반보정시스템(SBAS: Satellite Based Augmentation System)의 하나인 OmniSTAR의 개요, 고정해에의 수렴시간(convergence time)을 분석한 결과, 동적모드(Dynamic mode)에서 약 39분, 정적모드(Static mode)에서 약 28분 소요되는 것으로 나타났다. 본 연구의 성과는 높은 정확도를 요구하지 않는 위치기반서비스(LBS: Location Based Service) 분야, 모바일 측위분야, 공간정보산업분야에 활용될 수 있을 것으로 사료된다.

• 한국환경과학회지
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• 제11권2호
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• pp.103-110
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• 2002

The position fixing usually is determined by triangulation, traverse surveying and astronomy surveying. However, when the station is moving, it is impossible to determine its position continuously by the former method. By a satellite positioning method(GPS), this problem can be solved. In our study, we used two methods to determine the length and coordinate of a point position. One is a kinematic GPS method and the other is a static one. Each is based on carrier phase measurement and employs a relative position technique. We implemented observation experiments such as Geodimeter and DGPS(Differential GPS) successfully. To estimate the accuracy between the kinematic and static methods, we compared the results of Geodimeter, the kinematic, and the static. The results showed that the static is relatively a little more accurate than the kinematic. However, in the kinematic mode, when we received the GPS data for a long time, we found that the kinematic also had a high accuracy value for the length survey Finally, we applied the GPS to Jeju Harbor Breakwater to examine the applicability of GPS for coastal ocean structure based on the kinematics and the statics, respectively.

• 제어로봇시스템학회논문지
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• 제16권2호
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• pp.126-133
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• 2010

Due to the deployment of various wireless networks originating from CDMA, GSM, and WLAN, it became very convenient to exchange information from one place to another. As compared with the traditional environments for one-way information distribution based on fixed radio frequency bands, the convenient wireless network environments will bring about many changes in positioning technologies based on global navigation satellites. Among the many changes to come, the reconfigurable receiver network is one of the most attractive concepts since it can be tailored to a specific application area among networked robots, formation flying, bridge monitoring, and traffic monitoring. As an initial study to develop a reconfigurable receiver network, this paper deals with the design and implementation of the key elements of the reconfigurable receiver netowork; server, broadcaster, and client. In the designed receiver network, a sever receives and decodes measurements from a reference receiver installed at a known location, a broadcaster processes and transfers the messages from servers to clients and manages connections with servers and clients, a client receives the messages from the broadcaster and performs differential positioning. A real-time experiment result is demonstrated to validate the functionalities of each network element.

• Journal of Positioning, Navigation, and Timing
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• 제10권4호
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• pp.263-269
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• 2021

The carrier-based differential global navigation satellite system (CD-GNSS) has been garnering significant attention as a promising technology for unmanned vehicles for its high accuracy. The CD-GNSS systems to be used for safety-critical applications should provide a certain level of integrity. The integrity of these systems must be analyzed under various conditions, including fault-free and satellite fault conditions. The systems should be able to detect the faults that can cause large biases on the user position errors and quantify the integrity risk by computing the protection level (PL) to protect the user against the faults that are left undetected. Prior work has derived and investigated the PL for the fault-free condition. In this study, the integrity of the CD-GNSS system under the fault condition is analyzed. The position errors caused by the satellite's fault are compared with the fault-free PL (PL_H0) to verify whether the integrity requirement can be met without computing the PLs for the fault conditions. The simulations are conducted by assuming the ephemeris fault, and the position errors are evaluated by changing the size of the ephemeris faults that missed detection. It was confirmed that the existing fault monitors do not guarantee that the position error under the fault condition does not exceed the PL_H0. Further, the impact of the faults on the position errors is discussed.