A novel approach to improve GNSS Precise Point Positioning during strong ionospheric scintillation: theory and demonstration

At equatorial latitudes, ionospheric scintillation is the major limitation in achieving high-accuracy GNSS positioning. This is because scintillation affects the tracking ability of GNSS receivers causing losses of lock and degradation on code pseudorange and carrier phase measurements, thus degrading accuracy. During strong ionospheric scintillation, such effects are more severe and GNSS users cannot rely on the integrity, reliability, and availability required for safety-critical applications. In this paper, we propose a novel approach able to greatly reduce these effects of scintillation on precise point positioning (PPP). Our new approach consists of three steps: 1) a new functional model that corrects the effects of range errors in the observables; 2) a new stochastic model that uses these corrections to generate more accurate positioning; and 3) a new strategy to attenuate the effects of losses of lock and consequent ambiguities re-initializations that are caused by the need to re-initialize the tracking. We demonstrate the effectiveness of our method in an experiment using a 30-day static dataset affected by different levels of scintillation in the Brazilian southeastern region. Even with limitations imposed by data gaps, our results demonstrate improvements of up to 80% in the positioning accuracy. We show that, in the best cases, our method can completely negate the effects of ionospheric scintillation and can recover the original PPP accuracy that would have existed without any scintillation. The significance of this paper lies in the improvement it offers in the integrity, reliability, and availability of GNSS services and applications.</p

GPS Availability and Positioning Issues When the Signal Paths are Aligned with Ionospheric Plasma Bubbles

Made available in DSpace on 2018-12-11T17:24:17Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-10-01Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)The propagation paths of signals through equatorial ionospheric irregularities are analyzed by evaluating their effects on Global Navigation Satellite System (GNSS) positioning and availability. Based on observations during 32 days by a scintillation monitor at São José dos Campos, Brazil, it was noted that there is a dominance of enhanced scintillation events for Global Positioning System (GPS) ray paths aligned with the azimuth angle of 345° (geographic northwest). This azimuth corresponds to the magnetic meridian that has a large westward declination angle in the region (21.4ºW). Such results suggest that the enhanced scintillation events were associated with GPS signals that propagated through plasma bubbles aligned along the direction of the magnetic field. It will be shown that, under this alignment condition, the longer propagation path length through plasma bubbles can result in more severe scintillation cases and more losses of signal lock, as supported by proposed statistics of bit error probability and mean time between cycle slips. Additionally, large precise positioning errors are also related to these events, as demonstrated by precise point positioning experiments.Instituto de Aeronáutica e Espaço IAE/Instituto Tecnológico de Aeronáutica ITAInstituto Federal de Educação Ciência e Tecnologia de São Paulo Campus Presidente Epitácio (IFSP-PEP)Centro de Estudos em Telecomunicações Pontifícia Universidade Católica do Rio de Janeiro (CETUC/PUC-Rio), Rua Marquês de São Vicente 225Instituto Tecnológico de Aeronáutica ITA/Instituto Nacional de Pesquisas Espaciais INPEInstituto Nacional de Pesquisas Espaciais INPEInstituto Tecnológico de Aeronáutica ITAUniversidade Estadual Paulista Júlio de Mesquita Filho UNESPUniversity of BathUniversidade Estadual Paulista Júlio de Mesquita Filho UNESPCNPq: 309013/2016-0CNPq: 310802/2015-6CNPq: 465648/2014-2CAPES: 88881.134266/2016-0

Cálculo dos vetores de posição e velocidade dos satélites GLONASS a partir das efemérides transmitidas e aspectos relacionados à sua integração com o GPS

This paper presents details on the estimation of position and velocity vectors for GLONASS satellites from their broadcasted ephemeris using forth-order Runge-Kutta integration method and deals with the compatibility between GLONASS ephemeris and GPS time system. Besides, we analyze the compatibility between GLONASS and GPS time systems. In order to assess the quality of the integration method the coordinates calculated were compared to the broadcasted ones. The mean discrepancy was 1.33 m with a standard deviation of ±0.83 m. Next, we showed how to make GPS and GLONASS (time) systems compatible by calculating GLONASS coordinates from broadcasted ephemeris in GPS time. The results were compared to the IGS coordinates. The mean discrepancy was 6.53 m which agrees with the GLONASS broadcasted ephemeris precision.Este trabalho apresenta detalhes sobre o cálculo dos vetores de posição e velocidade dos satélites GLONASS a partir de suas efemérides transmitidas, utilizando o método de integração de Runge-Kutta de quarta ordem e a compatibilização das efemérides GLONASS (GLobal Orbiting NAvigation Sattelite System) com o sistema de tempo GPS (Global Positioning System). Também é feita uma análise da compatibilização entre os sistemas de tempo GLONASS e GPS. Para análise da qualidade do método de integração, as coordenadas extrapoladas foram comparadas às coordenadas transmitidas. A média das discrepâncias foi de 1,33 m, com desvio padrão de ±0,83 m. Para demonstrar a compatibilização entre os sistemas (de tempo) GPS e GLONASS, as coordenadas GLONASS calculadas a partir das efemérides transmitidas foram comparadas com as coordenadas precisas geradas pelo IGS no tempo GPS. A discrepância média foi de 6,53 m, menor que a precisão (divulgada) das efemérides transmitidas para o GLONASS. Em seguida, foi feita a compatibilização entre os sistemas (de tempo) GPS e GLONASS ao se calcular as coordenadas GLONASS a partir das efemérides transmitidas, no tempo GPS

Impact and synergies of GIM error estimates on the VTEC interpolation and single-frequency PPP at low latitude region

The vertical total electron content (VTEC) is one of the key quantities to describe variations of the ionosphere and can be provided to users to correct the ionospheric disturbances for GNSS (Global Navigation Satellite System) positioning. The VTEC values and the corresponding standard deviations are routinely provided in the so-called Global Ionosphere Maps (GIM), with a typical time resolution of 2 h (and up to 15 min) on regular grids with 2.5º resolution in latitude and 5º resolution in longitude. To determine the ionospheric corrections from the GIMs for positioning applications, an interpolation has to be applied to the VTEC grid values, which generally degenerates the final VTEC accuracy. In this context, the typically applied bi-linear interpolation of the VTEC values is calculated by introducing a new weighting scheme by means of the standard deviation maps in the ionospheric domain. In the sequel, the impact of the use of the VTEC uncertainties for the interpolation procedure is applied to the GIMs of different centers and assessed in the ionospheric and in the positioning domain. For the assessment of the GIM in the ionospheric domain, the VTEC values calculated are compared with VTEC directly obtained from the given GIM, i.e., without interpolation. In the positioning domain, the impact of the VTEC uncertainties is analyzed by means of single-frequency precise point positioning (PPP), considering four Brazilian stations in challenging regions. The use of the standard deviation values in positioning provides a significant improvement in periods of high solar flux, especially for stations in the region under more intense ionospheric effect (mean rates of improvements up to 47%).We acknowledge the IGS IAACs, in particular, CODE, for providing the ionospheric data, IBGE for providing the GNSS data and the National Institute of Science and Technology for GNSS in Support of Air Navigation (INCT GNSS-NavAer), funded by CNPq (465648/2014-2), FAPESP (2017/50115-0) and CAPES (88887.137186/2017-00).This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001 and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP: 2021/05285-0) with the support as well of the UPC

Two‐way assessment of ionospheric maps performance over the Brazilian region : Global versus regional products

Vertical total electron content (VTEC) has great importance in describing the ionosphere. VTEC values are commonly distributed in regular grids by means of so-called global ionospheric maps (GIMs) and regional ionospheric maps (RIMs). Although considerable research has been conducted to develop regional and global models, there is no clear understanding of the benefits of using RIMs over GIMs. Aiming to contribute to this discussion, our investigation presents a comparison between seven global and regional ionospheric maps considering two approaches: (a) ionosonde data-based assessment and (b) global navigation satellite systems (GNSS) positioning assessment. A challenging low latitude ionosphere scenario, the Brazilian region, was selected during a week with an active geomagnetic storm. The assessment results with ionosonde data have shown better performance of the RIM products named OTHR and OTRG. Among the global products, CODG and UQRG have shown the best performances. The worst results were obtained with the RIM named Instituto Nacional de Pesquisas Espaciais. The assessment with GNSS positioning led to larger and noisier errors close to the equatorial anomaly. Two of the analyzed RIMs presented expected large errors in stations at the edges of the coverage area. To overcome this issue, a hybrid product was proposed to extend the RIM covered region. The proposed hybrid product (OTRG) presented the best results in the GNSS positioning domai

GPS Availability and Positioning Issues When the Signal Paths are Aligned with Ionospheric Plasma Bubbles

The propagation paths of signals through equatorial ionospheric irregularities are analyzed by evaluating their effects on Global Navigation Satellite System (GNSS) positioning and availability. Based on observations during 32 days by a scintillation monitor at São José dos Campos, Brazil, it was noted that there is a dominance of enhanced scintillation events for Global Positioning System (GPS) ray paths aligned with the azimuth angle of 345° (geographic northwest). This azimuth corresponds to the magnetic meridian that has a large westward declination angle in the region (21.4ºW). Such results suggest that the enhanced scintillation events were associated with GPS signals that propagated through plasma bubbles aligned along the direction of the magnetic field. It will be shown that, under this alignment condition, the longer propagation path length through plasma bubbles can result in more severe scintillation cases and more losses of signal lock, as supported by proposed statistics of bit error probability and mean time between cycle slips. Additionally, large precise positioning errors are also related to these events, as demonstrated by precise point positioning experiments