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@InProceedings{LimaFoMaSoSaPaMo:2019:EtDiLb,
               author = "Lima Filho, Vicente Carvalho and Marini, Leonardo Pereira and 
                         Soussantos, Jonas and Salles, Lucas Alves and Paula, Eurico 
                         Rodrigues de and Moraes, Alison O.",
          affiliation = "{Instituto Tecnol{\'o}gico de Aeron{\'a}utica (ITA)} and 
                         {Instituto Tecnol{\'o}gico de Aeron{\'a}utica (ITA)} and 
                         {Instituto Tecnol{\'o}gico de Aeron{\'a}utica (ITA)} and 
                         {Instituto Tecnol{\'o}gico de Aeron{\'a}utica (ITA)} and 
                         {Instituto Nacional de Pesquisas Espaciais (INPE)} and {Instituto 
                         de Aeron{\'a}utica e Espa{\c{c}}o (IAE)}",
                title = "The eta-mi distribution for L-band ionospheric amplitude 
                         scintillation modeling and the evaluation of GBAS CAT I services 
                         under low latitude regions",
                 year = "2019",
         organization = "ION International Technical Meeting",
             abstract = "The usage of the GNSS is a world trend among the new technologies 
                         for air navigation. Within this context, the FAA developed the 
                         Ground-Based Augmentation System (GBAS) to improve accuracy, 
                         integrity, and continuity of the GNSS positioning through the 
                         augmentation of the GPS observables, in order to support precision 
                         approach landings. The GBAS can be considered a safety-critical 
                         system due to the precision landing requirements defined by ICAO. 
                         The ionospheric layer generates significant interference in the 
                         satellite signals and is one of the most threatening issues for 
                         the GBAS. Ionospheric scintillation may cause severe damage in the 
                         GPS receiver tracking loop operations. In moderated events, 
                         scintillation can reduce the accuracy of GPS pseudorange and 
                         carrier measurements, but the receiver still remains in lock. The 
                         tracking loop performance is degraded by scintillation fades that 
                         eventually lead to cycle slips. However, during strong 
                         scintillation events, the receiver might not be able to handle the 
                         large amount of scintillation, loosing its channels because the 
                         signal-to-noise ratio drops below the receiver threshold, 
                         resulting in a loss of lock. The strong amplitude scintillation 
                         phenomena are usual around the equatorial and low-latitude 
                         regions, in a belt of approximately 20o of geomagnetic latitude. 
                         These pronounced scintillation events are related to the presence 
                         of depleted structures known as Equatorial Plasma Bubbles (EPBs). 
                         EPBs rise in the equatorial and low-latitude regions in the 
                         nighttime due to the electrodynamic features in the equatorial 
                         plasma bulk. In the equatorial and low-latitude region, after the 
                         dusk, the elevation uplift of the plasma implies larger vertical 
                         gradients in an opposite direction of the gravity forcing, thus 
                         setting the system into an unstable equilibrium. If an external 
                         perturbation exists, then this equilibrium may be disturbed and 
                         the Rayleigh-Taylor instability action may cause the evolution of 
                         such kilometric bubble structures. After this initial step, a 
                         cascading process originates structures progressively smaller, 
                         whose wavelength will interfere deeply in the satellite 
                         transionospheric L-band signals causing the strong amplitude 
                         scintillation. In the Brazilian territory such events are more 
                         intense during spring and summer months, under high solar flux 
                         conditions. Nowadays, scintillations due to plasma bubbles 
                         affecting satellites signals during the night are the most 
                         significant issues that forbid Brazil from providing CAT I 
                         services from a GBAS station, considering the current architecture 
                         of the system available. This work analyzes high rate (50Hz) 
                         measurements of the GPS L1 (1.575GHz) amplitude scintillation data 
                         recorded during one month between December 2001 and January 2002 
                         at S{\~a}o Jos{\'e} dos Campos, Brazil (Geographic coordinates: 
                         23.20o S, 45.86o W, -17.50o dip latitude), a place located near to 
                         the southern crest of the equatorial ionization anomaly. The goal 
                         of this study is to evaluate the use of eta-mi probability density 
                         function in the statistical characterization of the ionospheric 
                         fading events. The analysis was performed comparing the proposed 
                         model against other models widely accepted in the literature, like 
                         Nakagami-m and Rice models, and additionally, the comparison is 
                         extended against the alpha-mi model. The results of the analysis 
                         performed showed that the eta-mi distribution presents good 
                         results on fitting empirical data of scintillation. This 
                         capability may help to better characterize fading events for 
                         example for GBAS availability studies. Typical pairs of eta-mi 
                         coefficients are presented as well as a discussion about the 
                         fading profile based on such values. The comparison of eta-mi 
                         distribution to Rice, Nakagami-m and alpha-mi models showed that 
                         eta-mi is capable of describing a wide range of scenarios with a 
                         fair adjustment in the tail of the distribution. This topological 
                         adjustment is an advantage of bivariate distributions like the 
                         alpha-mi and eta-mi models in comparison with the single parameter 
                         distributions. The fit test results show that the alpha-mi 
                         distribution has a similar performance to the eta-mi model, both 
                         providing a flexibility that better adjusts to the measured data, 
                         in particular in the tail of the distribution. Additionally, in 
                         this work the estimation of the fading coefficients eta-mi is 
                         explored according to the experimental data, providing empirical 
                         values for theoretical works and discussing the benefits of this 
                         proposed model and other models adopted in the literature. 
                         Equations presenting an approximation useful for theoretical works 
                         are also proposed based on the results. Finally, a discussion 
                         about the bit error probability and mean time between cycle slips 
                         is also included showing estimated values using the eta-mi model. 
                         Based on these results, it is analyzed how this geophysical 
                         phenomenon may generate unacceptable threatening gradients that, 
                         occasionally, will restrict GBAS to operate safely during the 
                         nighttime in low latitude regions.",
  conference-location = "Reston, Virginia",
      conference-year = "28-31 jan.",
             language = "en",
        urlaccessdate = "29 nov. 2020"
}


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