• Journal of Positioning, Navigation, and Timing
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• 제7권3호
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• pp.183-188
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• 2018

The Global Navigation Satellite System (GNSS) signal gets delayed as it goes through the troposphere before reaching the GNSS antenna. Various tropospheric models are being used to correct the tropospheric delay. In this study, we compared effectiveness of two popular troposphere correction models: Global Pressure and Temperature (GPT) and Satellite-Based Augmentation System (SBAS). One-year data from a particular site was chosen as the test case. Tropospheric delays were computed using the GPT and SBAS models and compared with the International GNSS Service tropospheric product. The bias of SBAS model computations was 3.4 cm, which is four times lower than that of the GPT model. The cause of higher biases observed in the GPT model is the fact that one cannot get wet delays from the model. If SBAS-based wet delays are added to the hydrostatic delays computed using the GPT model, then the accuracy is similar to that of the full SBAS model. From this study, one can conclude that it is better to use the SBAS model than to use the GPT model in the standard code-pseudorange data processing.

• Journal of Positioning, Navigation, and Timing
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• 제9권2호
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• pp.71-77
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• 2020

KRS which is subsystem of Korea Augmentation Satellite System (KASS) performs a role of collecting and monitoring GPS signals. In order to generate the accurate correction message, the site which meets the requirements should be selected and verification to meet each requirement should be accompanied. When the sites are selected, the environmental considerations are EMI, clear horizon (CH) and multipath. Of these, EMI and CH can be checked for satisfaction by instrumentation, but multipath error is difficult to predict. Therefore, multipath error analysis for the installation position of actual antenna at each KRS site should be preceded, and multipath scenario should be generated for each location to analyze the effects of the resulting system performance. In this paper, based on satellite signals collected from each KRS sites, the method for analyzing multipath error in each KRS sites is described, and the multipath error is analyzed. Also to perform an analysis of the effects on system performance due to multipath error, multipath error modeling is performed for the generation of simulation scenarios.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.1
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• pp.417-421
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• 2006

ICAO defines performance requirements of navigation system such as accuracy, integrity, continuity and availability. The integrity is most significant performance requirement in aviation where safety of life is crucial. Many researches on this topic anticipate that GPS with SBAS or Galileo can meet APV requirements and GPS with GBAS or Galileo with GBAS will meet CAT II and III requirements. These performance expectations are based on global analysis. In this paper regional integrity analysis in Korea using various combinations of modernized GPS, Galileo and SBAS is given. The simulation results show that CAT I requirement can be met using modernized GPS and Galileo alone, however, CAT II and III are not met even augmenting SBAS because of VPL. A more efficient augmentation such as GBAS which can reduce VPL dramatically is required to meet CAT II and III in Korean region.

• 한국항해항만학회지
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• 제31권10호
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• pp.859-864
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• 2007

미래 항만내 항법에서 요구하는 sub-meter 수준의 위치정확도를 만족하기 위해 DGPS와 같은 위성전파항법 보강시스템의 활용이 필요하다. 일반적으로 해양에서 사용하는 DGPS 기준국용 수신기는 RSIM Ver. 1.1에서 제시한 DGPS 기준국용 수신기 성능 요구사항을 만족해야 하고, 이에 대한 성능검증이 필요하다. 본 논문에서는 해양에서 사용하는 DGPS 기준국용 수신기의 성능검증방법을 제안하였다. 그리고 제안한 DGPS 기준국용 수신기 성능검증 방법으로 실시한 상용 DGPS 기준국용 수신기의 성능검증 실험을 통하여 제안한 성능검증 방법을 검증하였다.

• Journal of Positioning, Navigation, and Timing
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• 제11권4호
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• pp.251-261
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• 2022

The Centimeter Level Augmentation Service (CLAS) is the Precise Point Positioning (PPP) - Real Time Kinematic (RTK) correction service utilizing the Quasi-Zenith Satellite System (QZSS) L6 (1278.65 MHz) signal to broadcast the Global Navigation Satellite System (GNSS) error corrections. Compact State-Space Representation (CSSR) corrections for mitigating GNSS measurement error sources such as satellite orbit, clock, code and phase biases, tropospheric error, ionospheric error are estimated from the ground segment of QZSS CLAS using the code and carrier-phase measurements collected in the Japan's GNSS Earth Observation Network (GEONET). Since the CLAS service begun on November 1, 2018, users with dedicated receivers can perform cm-level precise positioning using CSSR corrections. In this paper, CLAS-based VRS-RTK performance evaluation was performed using Global Positioning System (GPS) observables collected from the refence station, TSK2, located in Japan. As a result of performing GPS-only RTK positioning using the open-source software CLASLIB and RTKLIB, it took about 15 minutes to resolve the carrier-phase ambiguities, and the RTK fix rate was only about 41%. Also, the Root Mean Squares (RMS) values of position errors (fixed only) are about 4cm horizontally and 7 cm vertically.

• Journal of Positioning, Navigation, and Timing
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• 제10권2호
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• pp.75-82
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• 2021

Fields of high-precision positioning applications are growing fast across the mass market worldwide. Accordingly, the industry is focusing on developing methods of applying State-Space Representation (SSR) corrections on low-cost GNSS receivers. Among SSR correction types, this paper analyzes Safe Position Augmentation for Real Time Navigation (SPARTN) messages being offered by the SAfe and Precise CORrection DAta (SAPCORDA) company and validates positioning algorithms based on them. The first part of this paper introduces the SPARTN format in detail. Then, procedures on how to apply Basic-Precision Atmosphere Correction (BPAC) and High-Precision Atmosphere Correction (HPAC) messages are described. BPAC and HPAC messages are used for correcting satellite clock errors, satellite orbit errors, satellite signal biases and also ionospheric and tropospheric delays. Accuracies of positioning algorithms utilizing SPARTN messages were validated with two types of positioning strategies: Code-PPP using GPS pseudorange measurements and PPP-RTK including carrier phase measurements. In these performance checkups, only single-frequency measurements have been used and integer ambiguities were estimated as float numbers instead of fixed integers. The result shows that, with BPAC and HPAC corrections, the horizontal accuracy is 46% and 63% higher, respectively, compared to that obtained without application of SPARTN corrections. Also, the average horizontal and vertical RMSE values with HPAC are 17 cm and 27 cm, respectively.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2008년도 춘계종합학술대회 A
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• pp.197-200
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• 2008

위성항법보강시스템은 위성항법시스템 (GNSS : Global Navigation Satellite System)의 측정값에 오차 성분을 제거하여 정밀한 항법 정보를 제공한다. 하지만 기준국과 이동국 사이의 공통오차는 제거할 수 있지만 전리층, 대류층, 신호잡음 등에 의해 발생하는 노이즈 성분의 비 공통오차는 제거할 수 없다. 본 논문에서는 다중 기준국을 사용하여 유동적인 전리층 및 대류층 습윤 증기량에 따라 비공통오차의 증가를 위치 오차 분산 변화를 통해 확인하였다.

• 한국항공우주학회지
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• 제35권12호
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• pp.1101-1107
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• 2007

본 논문에서는 GPS, GPS 현대화, Galileo, SBAS 및 GBAS등의 항법 시스템을 모두 고려하여 한국 지역에서의 GNSS 무결성 감시의 가용성을 분석하였다. 현대화된 GPS, Galileo 및 SBAS를 사용하면 Cat. I에 근접한 성능을 얻을 수 있음을 시뮬레이션을 통해 확인 하였다. 그러나 여전히 수직오차의 영향으로 Cat. II 및 III를 만족시키지 못하므로 GBAS와 같은 보다 개선효과가 큰 보강 항법 시스템이 필요함을 확인하였다. 본 논문의 연구 결과는 보강시스템의 구축뿐 아니라 지역 위성항법시스템 구축을 위한 기초 자료로 활용될 수 있다.

• 한국위성정보통신학회논문지
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• 제8권1호
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• pp.40-44
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• 2013

본 논문에서는 지상용 GPS(Global Positioning System)와 유사한 GBAS(Ground Based Augmentation Systems)의 위치측정오차에 대해서 연구하였다. GBAS의 위치측정오차에 영향을 주는 요소는 많이 있으며 측위오차(DOP: Dilution Of Precision)도 그 중의 하나이다. 측위오차는 송신기와 수신기의 수와 기하학적 배치위치에 따라서 결정된다. 본 연구에서는 한반도 지형에 2-열로 송신기를 배치하고 수신기의 위치에 따른 고도별 DOP를 예측할 수 있는 알고리즘을 개발하였다. 본 논문은 송신기와 수신기가 배치된 3차원 공간의 DOP를 정확하게 예측할 수 있어서 항법시스템에 매우 유용하게 사용될 수 있을 것으로 판단된다.

• 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.