• 한국항공우주학회지
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• 제38권10호
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• pp.979-984
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• 2010

GPS/Galileo 통합 수신기를 사용하는 사용자는 특정 측위 시스템에 대한 의존도를 줄이고, 개선된 성능의 PNT 서비스를 제공받을 수 있을 것으로 예상된다. 그러나 사용자들은 GPS와 Galileo, 두 시스템 간의 서로 다른 시각 척도를 사용함으로써 발생하는 문제(즉, GGTO)를 해결해야만 한다. GGTO는 측위 서비스를 요구하는 항법용 수신기뿐만 아니라 정밀한 시각 서비스를 요구하는 타이밍용 수신기에서도 분석되어야 한다. 본 논문에서는 GPS/Galileo 통합 타이밍용 수신기를 사용할 때에 고려해야 하는 상호운용성 문제를 분석하고, 모의실험을 통해 다양한 가정 하에 시각 측면에서의 성능을 예측하였다. Ashtech 사(社)의 상용 타이밍용 수신기를 사용하여 GPS 실측 데이터를 확보하고, Galileo 데이터를 모사한 후에, 타이밍용 환경에 적합한 실험 시나리오를 구성하여, 시나리오 별시각 측면에서의 성능을 평가하였다.

• Journal of Astronomy and Space Sciences
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• 제26권4호
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• pp.547-554
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• 2009

AIRS는 미국 NASA의 지구관측위성인 Aqua에 탑재되어 있으며, 적외선 채널을 이용하여 지구 대기의 수증기량을 관측한다. 이 논문에서는 AIRS 적외선 관측데이터를 이용하여 인천에 소재한 GPS 상시관측소 상공에 분포하는 가강수량을 추출하고, 이를 GPS 추정치와 비교하였다. 그 결과 AIRS에서 관측된 가강수량과 GPS 가강수량은 거의 비슷한 경향을 보였으며, GPS 가강수량을 기준으로 편향 0.3cm, RMSE 0.7cm의 정확도를 달성하였다. GPS 가강수량과 AIRS 가강수량의 상관관계 분석 결과 0.89의 높은 상관계수를 보여 AIRS 가강수량이 지역적 특성을 비교적 잘 반영함을 알 수 있었다.

• Journal of Positioning, Navigation, and Timing
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• 제7권3호
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• pp.155-163
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• 2018

This study examined methods to enhance navigation performance and reduce the divergence of navigation solutions that may occur in the event of global positioning system (GPS) failure by integrating the GPS/inertial navigation system (INS) with the three-dimensional (3D) magnetic vector measurements of a magnetometer. A magnetic heading aiding method that employs a magnetometer has been widely used to enhance the heading performance in low-cost GPS/INS navigation systems with insufficient observability. However, in the case of GPS failure, wrong heading information may further accelerate the divergence of the navigation solution. In this study, a method of integrating the 3D magnetic vector measurements of a magnetometer is proposed as a countermeasure for the case where the GPS fails. As the proposed method does not require attitude information for integration unlike the existing magnetic heading aiding method, it is applicable even in case of GPS failure. In addition, the existing magnetic heading aiding method utilizes only one-dimensional information in the heading direction, whereas the proposed method uses the two-dimensional attitude information of the magnetic vector, thus improving the observability of the system. To confirm the effect of the proposed method, simulation was performed for the normal operation and failure situation of GPS. The result confirmed that the proposed method improved the accuracy of the navigation solution and reduced the divergence speed of the navigation solution in the case of GPS failure, as compared with that of the existing method.

• Journal of Positioning, Navigation, and Timing
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• 제9권4호
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• pp.357-366
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• 2020

This paper addressed a relative navigation method for autonomous rendezvous and docking of cube-satellites using single frequency Differential GPS (DGPS) under the intermittent communication between satellites. Since the ionospheric error of GPS measurement is variable depending on the visible satellites, a few meters error of relative navigation is occurred in the Low-Earth Orbit (LEO) environment. Therefore, it is essential to remove the ionospheric error to perform relative navigation. Besides, an intermittent communication period for receiving GPS measurements of the target satellite is limited for getting information every sampling time. To solve this problem, a method combining range domain DGPS and orbit propagation is proposed in this paper. The proposed method improves the performance of DGPS by using Hatch filter and solves an intermittent communication problem by estimating the relative position and velocity using Hill-Clohessy-Wiltshire Equation. Through the simulation, it is verified that the suggested algorithm provides the relative position error within RMS 0.5 m and the relative velocity error within RMS 3 cm/s. Furthermore, it has the advantage that it is suitable for real-time implementation using single-frequency GPS measurements and is computationally efficient.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.1
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• pp.141-144
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• 2006

The deviations in the injection orbital parameters, resulting from launcher dispersions, need to be estimated and used for autonomous satellite operations. For the proposed small satellite mission of the university there will be two GPS receivers onboard the satellite to provide the instantaneous orbital state to the onboard data handling system. In order to meet the power requirements, the satellite will be sun-tracking whenever there is no imaging operation. For imaging activities, the satellite will be maneuvered to nadir-pointing mode. Due to such different modes of orientation the geometry for the GPS receivers will not be favorable at all times and there will be instances of poor geometry resulting in no output from the GPS receivers. Onboard the satellite, the orbital information should be continuously available for autonomous switching on/off of various subsystems. The paper presents the strategies to make use of small arcs of data from GPS receivers to compute the mean orbital parameters and use the updated orbital parameters to calculate the position and velocity whenever the same is not available from GPS receiver. Thus the navigation message from the GPS receiver, namely the position vector in Earth-Centered-Earth-Fixed (ECEF) frame, is used as measurements. As for estimation, two techniques - (1) batch least squares method, and (2) Kalman Filter method are used for orbit estimation (in real time). The performance of the onboard orbit estimation has been assessed based on hardware based multi-channel GPS Signal simulator. The results indicate good converge even with short arcs of data as the GPS navigation data are generally very accurate and the data rate is also fast (typically 1Hz).

• Journal of Positioning, Navigation, and Timing
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• 제2권1호
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• pp.59-65
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• 2013

The signal broadcast from a GPS satellite experiences code delay and carrier phase advance while passing through the ionosphere, which causes a signal error. Many ionosphere models have been studied to correct this ionospheric delay error. In this paper, the ionosphere modeling for the Korean Peninsula was carried out using a spherical harmonics based model. In contrast to the previous studies, we considered a real-time ionospheric delay correction model using fewer number of basis functions. The modeling performance was evaluated by comparing with a grid model. Total number of basis functions was set to be identical to the number of grid points in the grid model. The performance test was conducted using the GPS measurements collected from 5 reference stations during 24 hours. In the test result, the modeling residual error was smaller than that of the existing grid model. However, when the number of measurements was small and the measurements were not evenly distributed, the overall trend was found to be problematic. For improving this problem, we implemented the modeling with additional virtual measurements.

• 제어로봇시스템학회논문지
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• 제7권11호
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• pp.944-952
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• 2001

Inertial navigation system(INS) errors increase with time due to inertial sensor errors, and therefore it is desired to combine INS with external aids such as GPS. However GPS informations have a randomly abrupt jump due to a sudden corruption of the received satellite signals and environment, and moreover GPS can\`t provide navigation solutions. In this paper, smoothing and prediction schemes are proposed for GPS`s jump or unavailable GPS. The smoothing algorithm which is designed as a scalar adaptive filter, smooths abrupt jump. The prediction algorithm which is proved by Schuler error model of INS, estimates INS error in appropriate time. The outputs of proposed algorithm apply stable measurements to GPS aided INS Kalman filter. Simulations show that the proposed algorithm can effectively remove measurement jump and predict INS error.

• 대한전자공학회논문지
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• 제27권2호
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• pp.158-165
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• 1990

정밀 시각비교를 위한 L1 대역(1575.42MHz), C/A 코드 GPS 수신기를 개발하여 성능평가를 하였다. 이 수신기를 이용하여 KSRI의 주 시계와 GPS 위성의 세슘 시계와의 GPS 측정을 100ns 이내의 정확도로 수행하였다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1997년도 한국자동제어학술회의논문집; 한국전력공사 서울연수원; 17-18 Oct. 1997
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• pp.1675-1678
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• 1997

In this paper, an attitude determination system(ADS) for KOMPSAT using GPS LI carrier phase measurements is considered. The baseline vector is estimated by the Exetnded Kalman Filter (EKF) which used the double differenced carrier phased measuremenmts made by three GPS receivers mounted on the spaceraft. The attitude angles of three axes of spacecrat are computed by the estimated baseline vectors, directly. The proposed ADS is verified by the simulation results.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.2325-2330
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• 2003

GPS based orbit determination system for the KOMPSAT-2 has been developed. Two types of orbit determination software such as operational orbit determination and precise orbit determination are designed and implemented. GPS navigation solutions from on-board the satellite are used for the operational orbit determination and raw measurements data such as C/A code pseudo-range and L1 carrier phase for the precise orbit determination. Operational concept, architectural design, software implementation, and performance test are described.