Contribution of Unesp on broadcast ephemeris and PDOP monitoring for GNSS in the IGMA - Trial Project
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2020-03-04
Autores
Siqueira, Loram
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Universidade Estadual Paulista (Unesp)
Resumo
A modernização do GNSS (Global Navigation Satellite System) com a inclusão de novas constelações e melhorias nos sistemas já disponíveis foi avaliada com grande interesse na última década. A combinação de diferentes constelações de satélite expande as aplicações possíveis; portanto, o termo multi-GNSS apareceu para designar o uso desses múltiplos sistemas. O IGS (International GNSS Service), observando a necessidade dos usuários que começaram a usar o multi-GNSS, lançou em 2011 a proposta de projeto experimental IGMA (International GNSS Monitoring Assessment). O projeto visa criar um sistema internacional de análise GNSS com resultados que apresentem confiabilidade para usuários em todo o mundo. Na chamada para a participação como centro de análise a FCT-Unesp foi aceita como parte do projeto para avaliar dois dos quatro parâmetros propostos: Diluição da Precisão da Posição (PDOP) e a acurácia das efemérides transmitidas. Dos sistemas disponíveis, quatro foram escolhidos: GPS, Galileo. GLONASS e BeiDou nessa pesquisa. Foi realizado um estudo sobre o estado da arte para as aplicações de PDOP e WPDOP (Diluição da precisão ponderada na posição). Nas análises de acurácia, foi utilizado a correção entre o centro de fase e o centro de massa do satélite para comparar corretamente as efemérides finais e as transmitidas durante 600 dias (os 120 primeiros dias de cada ano entre 2015 e 2019). O GPS apresentou um RMSE 3D de 1,94 m, Galileo 1,19 m, GLONASS 7,21 m e BeiDou 3,19 m. As análises do PDOP e WPDOP foram realizadas para avaliar a correlação desses elementos com a qualidade do posicionamento por ponto simples. Para o WPDOP foi utilizado um modelo de ponderação que considerou o ângulo de elevação do satélite já proposto na literatura. Uma estação da RBMC (BRAZ) foi escolhida para realização do experimento. Doze dias foram escolhidos, os quais representam variações nos elementos que influenciarão a transmissão do sinal na atmosfera: troposfera e ionosfera. O coeficiente de correlação entre o PDOP e o erro 3D foi classificada como não correlacionada em 25% dos dias, fracamente relacionada para o restante. O WPDOP teve uma correlação moderada com o erro 3D em 84% dos dias e fracamente correlacionada no restante. O projeto de teste da IGMA é uma boa oportunidade para a comunidade GNSS abordar tópicos importantes sobre a modernização dos sistemas de navegação. Sobre a precisão das efemérides transmitidas, esta pesquisa mostrou que cada sistema tem uma acurácia que precisa ser considerada ao combiná-los para o posicionamento. Para o PDOP, observa-se que o aumento no número de satélites e, portanto, o valor de PDOP diminuir não reflete em uma melhor qualidade do posicionamento. O WPDOP mostrou que a inclusão de informações com significado físico pode fornecer uma correlação mais alta entre esse valor e o erro 3D de um posicionamento de ponto simples.
The modernization of GNSS (Global Navigation Satellite System) with the inclusion of new constellations and improvements in the already available systems has been assessed with great interest over the last decade. The combination of different satellite constellations expands the possible applications, so the term multi-GNSS appeared to designate the use of these multiple navigation systems. The IGS (International GNSS Service), observing the need of the users who started using multi-GNSS, launched in 2011 the proposal for the IGMA (International GNSS Monitoring Assessment) trial Project. It aims to create an international GNSS analysis system with results that present reliability for users around the world. In the call for participation as a center of analysis, FCT-Unesp was accepted as part of the trial project to evaluate the following parameters: Position Dilution of Precision (PDOP) and the accuracy of the broadcast ephemeris. Of the available systems, four were chosen: GPS, Galileo, GLONASS e BeiDou. A state-of-the-art study of PDOP and WPDOP (Weighted Position Dilution of Precision) applications was performed. On the accuracy analysis, it was used the phase center vector to correctly compare the final and broadcast ephemeris for 600 days (the first 120 days for each year between 2015 and 2019). The results show that GPS had an overall RMSE of 1.94 m, Galileo 1.94 m, GLONASS 7.21 m and BeiDou 3.19 m. The PDOP and WPDOP analyzes were carried out to evaluate the correlation of these elements with the quality of a standard point positioning. For WPDOP it was used a weighting model that considered the satellite elevation angle. A known station from the RBMC (BRAZ) was used for the analysis. Twelve days were chosen to represent variations on the elements that would influence the signal transmission in the atmosphere: Troposphere and Ionosphere. The correlation between the PDOP and the 3D error presented as no correlated for 25% of the days and weekly correlated remaining ones. The WPDOP had a moderate correlation with the 3D error on 84% of the days and strongly correlated to the other days. The IGMA trial project is a good opportunity for the GNSS community to address important topics on the modernization of navigation systems. On the broadcast accuracy this research showed that each GNSS has an accuracy that needs to be considered when combining them for positioning. For the PDOP it shows that increasing the number of satellites and therefore decreasing the PDOP value does not reflect in a higher reliability of the positioning. WPDOP showed that including information that have physical meaning can give a higher correlation between this value and the 3D error of a standard point positioning.
The modernization of GNSS (Global Navigation Satellite System) with the inclusion of new constellations and improvements in the already available systems has been assessed with great interest over the last decade. The combination of different satellite constellations expands the possible applications, so the term multi-GNSS appeared to designate the use of these multiple navigation systems. The IGS (International GNSS Service), observing the need of the users who started using multi-GNSS, launched in 2011 the proposal for the IGMA (International GNSS Monitoring Assessment) trial Project. It aims to create an international GNSS analysis system with results that present reliability for users around the world. In the call for participation as a center of analysis, FCT-Unesp was accepted as part of the trial project to evaluate the following parameters: Position Dilution of Precision (PDOP) and the accuracy of the broadcast ephemeris. Of the available systems, four were chosen: GPS, Galileo, GLONASS e BeiDou. A state-of-the-art study of PDOP and WPDOP (Weighted Position Dilution of Precision) applications was performed. On the accuracy analysis, it was used the phase center vector to correctly compare the final and broadcast ephemeris for 600 days (the first 120 days for each year between 2015 and 2019). The results show that GPS had an overall RMSE of 1.94 m, Galileo 1.94 m, GLONASS 7.21 m and BeiDou 3.19 m. The PDOP and WPDOP analyzes were carried out to evaluate the correlation of these elements with the quality of a standard point positioning. For WPDOP it was used a weighting model that considered the satellite elevation angle. A known station from the RBMC (BRAZ) was used for the analysis. Twelve days were chosen to represent variations on the elements that would influence the signal transmission in the atmosphere: Troposphere and Ionosphere. The correlation between the PDOP and the 3D error presented as no correlated for 25% of the days and weekly correlated remaining ones. The WPDOP had a moderate correlation with the 3D error on 84% of the days and strongly correlated to the other days. The IGMA trial project is a good opportunity for the GNSS community to address important topics on the modernization of navigation systems. On the broadcast accuracy this research showed that each GNSS has an accuracy that needs to be considered when combining them for positioning. For the PDOP it shows that increasing the number of satellites and therefore decreasing the PDOP value does not reflect in a higher reliability of the positioning. WPDOP showed that including information that have physical meaning can give a higher correlation between this value and the 3D error of a standard point positioning.
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Palavras-chave
Efemérides transmitidas, Acurácia, WPDOP, Broadcast ephemeris, Accuracy