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Inertial measurement units (IMUs) are key components of various applications including navigation, robotics, aerospace, and automotive systems. IMU sensor characteristics have a significant impact on the accuracy and reliability of these applications. In particular, noise characteristics and bias stability are critical for proper filter settings to perform a combined GNSS/IMU solution. This paper presents an analysis based on the Allan deviation of different IMU sensors that correspond to different grades of micro-electromechanical systems (MEMS)-type IMUs in order to evaluate their accuracy and stability over time. The study covers three IMU sensors of different grades (ascending order): Rokubun Argonaut navigator sensor (InvenSense TDK MPU9250), Samsung Galaxy Note10 phone sensor (STMicroelectronics LSM6DSR), and NovAtel PwrPak7 sensor (Epson EG320N). The noise components of the sensors are computed using overlapped Allan deviation analysis on data collected over the course of a week in a static position. The focus of the analysis is to characterize the random walk noise and bias stability, which are the most critical for combined GNSS/IMU navigation and may differ or may not be listed in manufacturers’ specifications. Noise characteristics are calculated for the studied sensors and examples of their use in loosely coupled GNSS/IMU processing are assessed. This work proposes a structured and reproducible approach for working with sensors for their use in navigation tasks in combination with GNSS, and can be used for sensors of different levels to supplement missing or incorrect sensor manufacturers’ data., This research was funded by Rokubun S.L. and Universitat Politècnica de Catalunya with industrial PhD grant number 2020 DI 108 from the Generalitat de Catalunya; This research was partially funded by the Spanish Ministry of Science and Innovation and European Union FEDER through projects CNS2022-135383 and PID2022-138485OB-I00., Peer Reviewed, Postprint (published version)

(English) Global Navigation Satellite System (GNSS) have revolutionized location and timing technologies due to their low cost and wide availability. Initially, GNSS was limited to the american Global Positioning System (GPS) and the Russian GLObal NAvigation Satellite System (GLONASS). However, in recent years, new GNSS systems such as European Global Navigation Satellite System (Galileo), the Chinese BeiDou Navigation Satellite System (BDS), the Japanese Quasi-Zenith Satellite System (QZSS), and Indian Regional Navigation Satellite System (IRNSS) have been deployed. These systems offer multiple frequencies and signals, which have rendered the current processing of dual-frequency single-constellation GNSS data obsolete. To address this issue, the Research group of Astronomy and Geomatics (gAGE) in Technical University of Catalonia (UPC) developed the GNSS-Lab Tool suite (gLAB) reference tool. Initially, gLAB was designed to support GPS only under a contract with the European Space Agency (ESA) and was later upgraded to become a reference tool for scientific studies. gLAB has demonstrated its research capabilities under ESA and European Union Agency for the Space Programme (EUSPA) contracts. The gLAB tool has had a great impact on the GNSS community across the globe, with 222,526 downloads from 147 different countries, which demonstrates the demand for a tool with these capabilities. The positioning algorithms originally coded in gLAB, Standard Point Positioning (SPP) and Precise Point Positioning (PPP), are upgraded to work with all new signals. In addition, advanced algorithms have been implemented, including uncombined PPP, Fast Precise Point Positioning (Fast-PPP), and Satellite-Based Augmentation System (SBAS) Dual Frequency Multi Constellation (DFMC). These additional capabilities required optimizing the code and implementing multi-threading to reduce processing times. The research carried out in this PhD has made several significant contributions. Firstly, an, (Català) El Sistema Global de Navegació per Satèl·lit (GNSS) ha revolucionat les tecnologies de localització gràcies al seu baix cost i àmplia disponibilitat. Inicialment, els GNSS es limitaven al Sistema de Posicionament Global (GPS) americà i al Sistema Global de Navegació per Satèl·lit (GLONASS) rus, però en els últims anys s'han desplegat nous GNSS com el Sistema Europeu de Navegació Global per Satèl·lit (Galileo), el Sistema de Navegació per Satèl·lit BeiDou (BDS) xinès, el Sistema de Satèl·lits Quasi Zenital (QZSS) japonès i el Sistema Regional Indi de Navegació per Satèl·lit (IRNSS). Aquests sistemes ofereixen múltiples freqüències i senyals que han deixat obsolet el processament actual de dades GNSS de doble freqüència i una constel·lació. Per a abordar aquest problema, el grup de Recerca en Astronomia i Geomàtica (gAGE) de la Universitat Politècnica de Catalunya (UPC) va desenvolupar l'eina GNSS-Lab Tool suite (gLAB). gLAB es va dissenyar inicialment per a suportar només GPS en el marc d'un contracte amb l'Agència Espacial Europea (ESA) i posteriorment es va actualitzar per a convertir-se en una eina de referència per a estudis científics. gLAB ha demostrat les seves capacitats de recerca en el marc de contractes de l'ESA i de l'Agència de la Unió Europea per al Programa Espacial (EUSPA). gLAB té un gran impacte en la comunitat GNSS de tot el món, amb 222.526 descàrregues en 147 països diferents, el qual demostra la demanda d'una eina amb aquestes capacitats. En quant als algorismes de posicionament codificats originalment en gLAB, Posicionament de Punt Estàndard (SPP) i Posicionament de Punt Precís (PPP), aquests han estat actualitzats per a treballar amb totes les noves senyals. A més a més, es van implementar algorismes avançats, com el PPP no combinat, el PPP Ràpid (Fast-PPP) i el Sistema de Augmentació Basat en Satèl·lits (SBAS) Multi Constel·lació de Freqüència Dual (DFMC). Aquestes capacitats addicionals han requerit l'optimització del codi i la impl, (Español) El Sistema Global de Navegación por Satélite (GNSS) ha revolucionado las tecnologías de localización gracias a su bajo coste y amplia disponibilidad. Inicialmente, los GNSS se limitaban al Sistema de Posicionamiento Global (GPS) estadounidense y al Sistema Global de Navegación por Satélite (GLONASS) ruso, pero en los últimos años se han desplegado nuevos GNSS como el Sistema Europeo de Navegación Global por Satélite (Galileo), el Sistema de Navegación por Satélite BeiDou (BDS) chino, el Sistema de Satélites Cuasi Cenitales (QZSS) japonés y el Sistema Regional Indio de Navegación por Satélite (IRNSS). Estos sistemas ofrecen múltiples frecuencias y señales que han dejado obsoleto el procesamiento actual de datos GNSS de doble frecuencia y una constelación. Para abordar este problema, el grupo de Investigación en Astronomía y Geomática (gAGE) de la Universidad Politécnica de Cataluña (UPC) desarrolló la herramienta GNSS-Lab Tool suite (gLAB). gLAB se diseñó inicialmente para soportar sólo GPS en el marco de un contrato con la Agencia Espacial Europea (ESA) y posteriormente se actualizó para convertirse en una herramienta de referencia para estudios científicos. gLAB ha demostrado sus capacidades de investigación en el marco de contratos de la ESA y de la Agencia de la Unión Europea para el Programa Espacial (EUSPA). gLAB tiene un gran impacto en la comunidad GNSS de todo el mundo, con 222.526 descargas en 147 países diferentes, lo que demuestra la demanda de una herramienta con estas capacidades. En cuanto a los algoritmos de posicionamiento codificados originalmente en gLAB, Posicionamiento de Punto Estándar (SPP) y Posicionamiento de Punto Preciso (PPP), éstos se han actualizado para trabajar con todas las nuevas señales. Además, se han implementado algoritmos avanzados, como el PPP no combinado, el PPP Rápido (Fast-PPP) y el Sistema de Aumentación Basado en Satélites (SBAS) Multi Constelación de Frecuencia Dual (DFMC). Estas capacidades adicionales han req, Postprint (published version)

(English) The characterization of Clock and Ephemeris error of the Global Navigation Satellite Systems is a key element to validate the assumptions for the integrity analysis of GNSS Safety of Life (SoL) applications. Specifically, the performance metrics of SoL applications require the characterization of the nominal User Range Errors (UREs) as well as the knowledge of the probability of a satellite, Psat or a constellation fault, Pconst, i.e. when one or more satellites are not in the nominal mode. We will focus on Advanced Autonomous Integrity Monitoring (ARAIM). The present dissertation carries-out an end-to-end characterization and analysis of Galileo and GPS satellites for ARAIM. It involves two main targets. First, the characterization of Galileo and GPS broadcast ephemeris and clock errors, to determine the fault probabilities Psat and Pconst, and the determination on an upper bound of the nominal satellite ranging accuracy (sURA). Second, using these experimental results, to assess the performance of the ARAIM at user level. With regard to the first goal, the main contribution has been the extension of the algorithms already developed for GPS satellites to the Galileo constellation. This is not a straightforward task, as it requires to consider the particular features of Galileo data. This characterization involved the development and implementation of complex algorithms to consolidate broadcast navigation files from a huge set of individual receivers, and using these consolidated files, to develop automatic monitors to assess the nominal behaviour of the GNSS satellites and detect anomalous events. The methodology has been applied to more than 5 years of Galileo data (since Galileo Open Service was declared on 15 December 2016) and more than 10 years of GPS data. Thanks to this analysis the satellite orbit and clock faults have been identified, the probability of failure established and sURA determined. The Not-to-Exceed (NTE) thresholds from Galileo commi, (Català) La caracterització dels errors de Rellotge i Efemèrides dels satèl·lits GNSS és un element clau per validar els supòsits per a l'anàlisi d'integritat dels sistemes d'augmentació GNSS "Safety-of-life" (SoL). Específicament, les mètriques de rendiment de les aplicacions SoL requereixen la caracterització dels errors nominals de rang d'usuari (URE), així com el coneixement de la probabilitat de fallada dels satèl·lits, Psat, o de les constel·lacions, Pconst, és a dir quan un o més satèl·lits no es troben en estat nominal. En particular, els resultats d'aquest treball s'apliquen a les tècniques avançades per al monitoratge autònom de la integritat de receptor (Advanced RAIM o ARAIM). En aquesta Tesi s'ha realitzat una caracterització i anàlisi d'extrem a extrem dels satèl·lits Galileu i GPS per a ARAIM. Això ha comportat dos objectius principals. En primer lloc, la caracterització dels errors les efemèrides i els errors de rellotge dels satèl·lits Galileo i GPS, per determinar les probabilitats de fallada Psat i Pconst, i la determinació dun límit superior de la precisió nominal en rang dels senyals de els satèl·lits (sURA). En segon lloc, la utilització dels resultats experimentals obtinguts per avaluar el rendiment de l¿ARAIM a nivell d¿usuari. Pel que fa al primer objectiu, la contribució principal d'aquesta tesi ha estat l'extensió dels algorismes ja desenvolupats per a GPS a la constel·lació Galileu. Tenint en compte les característiques particulars dels satèl·lits Galileo, s'han desenvolupat i implementat algorismes complexos per consolidar els missatges de navegació dels satèl·lits recollits per un gran conjunt de receptors individuals. Un cop consolidats, s'han desenvolupat monitors automàtics per avaluar el comportament nominal dels satèl·lits i detectar esdeveniments anòmals. La metodologia s'ha aplicat a més de 5 anys de dades de Galileo (des que es va declarar el servei obert el 15 de desembre de 2016 --Galileo IS OS--) i a més de 10 anys de dades G, (Español) La caracterización de los errores de Reloj y Efemérides de los satélites GNSS es un elemento clave para validar los supuestos para el análisis de integridad de los sistemas de aumentación GNSS "Safety-of-life" (SoL). Específicamente, las métricas de rendimiento de las aplicaciones SoL requieren la caracterización de los errores nominales de rango de usuario (URE), así como el conocimiento de la probabilidad de fallo de los satélites, Psat o de las constelaciones, Pconst, es decir cuando uno o más satélites no se encuentran en estado nominal. En particular los resultados de este trabajo se aplican a las técnicas avanzadas para la monitorización autónoma de la integridad de receptor (Advanced RAIM o ARAIM). En esta Tesis se ha realizado una caracterización y análisis de extremo a extremo de los satélites Galileo y GPS para ARAIM. Ello ha comportado dos objetivos principales. En primer lugar, la caracterización de los errores las efemérides y los errores de reloj de los satélites Galileo y GPS, para determinar las probabilidades de fallo Psat y Pconst, y la determinación de un límite superior de la precisión nominal en rango de las señales de los satélites (sURA). En segundo lugar, la utilización de los resultados experimentales obtenidos para evaluar el rendimiento del ARAIM a nivel de usuario. Respecto al primer objetivo, la principal contribución de esta tesis ha sido la extensión de los algoritmos ya desarrollados para GPS a la constelación Galileo. Teniendo en cuenta las características particulares de los satélites Galileo, se han desarrollado e implementado algoritmos complejos para consolidar los mensajes de navegación de los satélites recogidos por un gran conjunto de receptores individuales. Una vez consolidados, se han desarrollado monitores automáticos para evaluar el comportamiento nominal de estos satélites y detectar eventos anómalos. La metodología se ha aplicado a más de 5 años de datos de Galileo (desde que se declaró el servicio abierto el, Postprint (published version)

Monitoring spatiotemporal variations of ionospheric vertical total electron content (VTEC) is crucial for space weather and satellite positioning. In the present study, an enhanced neural network (ENN) model is proposed to capture the changing characteristics of ionospheric VTEC and compared with the traditional mathematical models, i.e. the POLYnomial (POLY) model, generalized trigonometric series function and spherical harmonic function (SHF) model. The ionospheric VTEC data obtained from 31 permanent global positioning system stations in the southwest region of China on 26 August and 8 September, 2017, were used to test the performance of the mentioned models under different Solar-geomagnetic conditions. The ENN model is derived from the ensemble learning method, and the disadvantage that simple backpropagation neural network learners that are not robust enough is weakened by the ENN model. After statistical analysis and single-frequency precise point positioning (SF-PPP) experiments, it is demonstrated that the ENN model is superior to the above three mathematical models, regardless of the solar-geomagnetic conditions. In terms of mean absolute error, root mean square error, standard deviation, and mean absolute percentage error, the ENN model outperforms the SHF model, which is the best mathematical model in the analysis, by 40.7%, 30.20%, 29.88%, 38.04% under quiet solar-geomagnetic conditions, and by 37.66%, 29.93%, 30.96%, 32.01% under active solar-geomagnetic conditions. In addition, the accuracy of the SF-PPP is greatly affected by the error caused by ionosphere. In the static SF-PPP experiment of this study, the ENN model can better correct ionospheric error. Under quiet and active solar-geomagnetic conditions, the SF-PPP accuracy can be improved by 85.1% and 85.2% with the ionosphere delay correction from the ENN model., Postprint (author's final draft)

Estimating inter-system biases (ISBs) is important in multi-constellation Global Navigation Satellite System (GNSS) processing. The present study aims to evaluate and screen out an optimal estimation strategy of ISB for multi-GNSS kinematic precise point positioning (PPP). The candidate strategies considered for ISB estimation are white noise process (ISB-WN), random walk process (ISB-RW), constant (ISB-CT) and eliminated by between-satellite single-differenced observations (ISB-SD). We first present the mathematical model of ISB derived from the observation combination among different GNSSs, and we demonstrate the equivalence between ISB-WN and ISB-SD in the Kalman filter. In order to evaluate the performance of these four ISB solution strategies, we implement kinematic PPP with 1-month static data from 112 International GNSS service stations and two-hour dynamic vehicular data collected in an urban case. For comparison, precise orbit and clock products from the Center for Orbit Determination in Europe (CODE), GeoForschungsZentrum in Germany (GFZ) and Wuhan University (WHU) are employed in our experiments. The results of static tests show that the positioning accuracy is comparable among the four strategies, but ISB-CT performs slightly better in convergence time. In the kinematic test, there are more cycle slips than static test, and the ISB-CT improves the positioning accuracy by 15.7%, 38.9% and 63.2% in east, north and up components, and reduces the convergence time by 60.1% comparing with the other strategies. Moreover, both the static and kinematic tests prove the consistence among CODE, GFZ and WHU precise products and the equivalence between ISB-WN and ISB-SD strategies. Finally, more, i.e., the same amount of cycle slips as for the dynamic data, are artificially added to the static data to conduct the pseudo-kinematic test. The result shows that ISB-CT improves the positioning accuracy and convergence time by 19.2% and 24.4%, respectively., The study is funded by Laoshan Laboratory (LSKJ202205104, LSKJ202205104_01), National Key Research and Development Program of China (2020YFB0505800, 2020YFB0505804), National Natural Science Foundation of China (42004012), Natural Science Foundation of Shandong Province, China (ZR2020QD048) and by the project RTI2018-094295-B-I00 funded by the MCIN/AEI 1013039/501100011033 which is co-funded by the FEDER program., Peer Reviewed, Postprint (published version)

In the present thesis a study is done regarding the viability and optimization of trajectories to get to the stability region around Lagrange points L4 and L5 from the Earth, specifically from periodic orbits around Lagrange points L1 and L2, in the frame of the circular restricted three-body problem of the Earth-Sun system. The trajectory of a spacecraft inside this stability region around L4 and L5 does not leave it for 1000 years or more and without the necessity of any maneuver, i.e. without fuel consumption. Furthermore, this region offers good positions to observe the Sun, and with that to be able to understand and predict the behaviour of possible space weather events, such as solar flares or coronal mass ejections. This is the set of reasons why this stability region is of scientific interest, so that the objective of the present thesis is to study how to get there in the most optimal way possible. Therefore, the unstable invariant manifolds that arise from the periodic orbits around L1 and L2 are the paths to consider as starting points for the transfer trajectories up to L4 and L5, as they take advantage of the dynamic nature of the circular restricted three-body problem. Once the stability region, the types of trajectories around L4 and L5 and the unstable invariant manifolds have been defined, it has been found that it is possible to reach L4 and L5 with a delta-V budget to perform the impulsive maneuvers of around 260 m/s, with times of flight between 8.5 and 9 years. However, it is possible to decrease the time of flight if the delta-V budget is increased, achieving 6-year transfers with delta-V budgets of around 400 m/s or 4-year transfers with delta-V budgets of around 550 m/s. These results show that there is a large variety of trajectories to choose to get to the equilibrium points L4 and L5, all them comparable, in flight times as well as in delta-V budget, to both current and past interplanetary missions. Therefore, it has been seen that there ar

Unmodeled errors play a critical role in improving the positioning accuracy of Global Navigation Satellite Systems. Few studies have addressed unmodeled errors in medium and long baselines using their time correlation, which is highly beneficial for achieving a precise and real-time solution. However, before tackling unmodeled errors, it is first necessary to determine reasonable basic functions to fit such unmodeled errors. Therefore, we study the selection of basic functions for time-varying unmodeled errors in two positioning modes: estimating atmospheric delays and using an IF combination. We choose three basic functions: polynomials, sinusoidal functions, and combinatorial functions. Fitting experiments and positioning experiments are conducted using the unmodeled error data provided by four baselines ranging from 30 to 220 km. The Root Mean Square Errors fitted by the second order are approximately 2 mm. The corresponding residuals generally converge to 3 mm in about 30 s. After correcting the observations using the fitted unmodeled errors of the second-order polynomial, the positioning results show improvements of about 40% to 80% in all directions. We conclude that the second-order polynomial is the optimal basic function in all two positioning modes., This study was supported by the National Natural Science Foundation of China (Project No. 41974030; 41674035). Jiafu Wang acknowledges financial support from the China Scholarship Council (Grant No. 202206090184). Adria Rovira acknowledges financial support from the Spanish Ministry of Science and Innovation projects: CNS2022-135383 and PID2022-138485OB-I00., Peer Reviewed, Postprint (published version)

The Circular-Restricted Three-Body Problem (CR3BP) describes the motion of a small celestial body in the gravitational field of two larger bodies. The present study focuses on the application of the CR3BP to the Sun-Earth system. To that end, the governing and defining equations for the CR3BP are described in-depth; and key periodic orbits around the Lagrange Points L1, L2, L4, and L5 are mapped. These last two points, located at the vertices of an equilateral triangle in the rotating frame of reference, are particularly useful for observation and exploration due to their stability. Thus, the L4 and L5 points are the final objective of the present study. The study focuses on optimizing transfer trajectories from the previously mapped orbits around L1 and L2 to orbits around L4 and L5, respectively. The procedures utilized significantly reduce the required delta-V budget to perform these transfers to approximately 3 km/s, a value lower than the minimum requirements for interplanetary transfers departing from Earth. This finding has the potential to open up new opportunities for asteroid science and solar observation based at the equilateral Lagrange Points of the Sun-Earth system; ultimately contributing to advancing the current era of scientific research in the field of astrodynamics.

Global Navigation Satellite System signals have been used for years to study high-frequency fluctuations (f>0.1Hz)intheionosphere. The customary procedure uses the geometry-free (GF) combination ofL1andL2carriers, for which it is necessaryto acquire theL2GPS signal. Initially,L2had to be acquired from a codeless signal, L2P(Y), using several techniques, someof them requiring the aid ofL1. New GPS satellites transmit the newC2civil code, which can be used to acquire directlyL2,i.e. L2C. Several publications have reported differences in the GF combination when it is computed from L2P(Y) or L2C.Using two ionospheric scintillation monitoring receivers (ISMRs), these differences were shown to be related to how theyacquireL2, i.e. if the receiver acquiresL2with theL1aid. However, ISMRs are scarce, so the extension of such a study is notstraightforward. The present work uses the geodetic detrending technique to identify whether a conventional geodetic-gradereceiver acquiresL2with the aid ofL1. The study employs six different receiver types with measurements stored in RINEXformats version 2 and 3. In both formats, we are able to identify ifL2signal is acquired withL1aid. In this way, we showthat some receiver types heavily underestimate high-frequency ionospheric fluctuations when using the GF combination.Our results show that the ionosphere-free combination of these carrier phases is not free from high-frequency ionosphericfluctuations, but in some receivers, almost 90% of the high-frequency effects inL1remain in such combination., Postprint (published version)

The first phase of the RT-WMIS activity comprises two Work Packages (WPs). WP 10 is aimed at performing a revision of the state-of-the-art RT products and requirements for the RT-WMIS activity. On the other hand, WP 20 is devoted to carry out the software design for the subsequent implementation of the RT-WMIS tool. The present technical note (TN-1) describes the activities developed in the framework of WP 10., Preprint

This research was funded by Albora Technologies and Universitat Politècnica de Catalunya with industrial PhD grant number DI 082 from the Generalitat de Catalunya; This research was partially funded by the Spanish Ministry of Science and Innovation project RTI2018-094295-B-I00. P.C. has been partially supported by the NSF under Awards CNS-1815349 and ECCS-1845833., Peer Reviewed, Postprint (author's final draft)

(English) Snapshot positioning is the technique to determine the position of a Global Navigation Satellite System (GNSS) receiver using only a very brief interval of the received satellite signal. In recent years, this technique has received a great amount of attention thanks to its unique advantages in power efficiency, Time To First Fix (TTFF) and economic costs for deployment. However, the state of the art algorithms regarding snapshot positioning were based on code measurements only, which unavoidably limited the positioning accuracy to meter level. The present PhD research aims at achieving high-accuracy (centimetre level) snapshot positioning by properly utilizing carrier phase measurements. Two technical challenges should be tackled before such level of accuracy can be achieved, namely, satellite transmission time inaccuracy and the so-called Data Bit Ambiguity (DBA) issue. The first challenge is essentially originated from the lack of absolute timing accuracy in the receiver, as only the coarse time information is available from an external assistance module and its error can be up to a few seconds. Applying a conventional Coarse Time Filter (CTF) can increase this timing accuracy to millisecond level. However, this is still not enough for carrier-phase based positioning since the satellite position errors introduced by such timing errors range up to one meter, which certainly impedes the carrier phase Integer Ambiguity Resolution (IAR). A method is proposed to set a global time tag and correspondingly construct the pseudoranges with full period corrections. The second challenge is caused by the fact that snapshot measurements are generated based on the results of the correlation between the received signal and the local replicas. Multiple replicas are typically produced in snapshot positioning following the Multi Hypothesis (MH) acquisition architecture. It may happen that more than one local replica (i.e. hypothesis) result in the maximum correlation energ, (Español) El posicionamiento instantáneo es la técnica para determinar la posición de un receptor del Sistema Global de Navegación por Satélite (GNSS) utilizando solo un intervalo muy breve de la señal recibida. En los últimos años, esta técnica ha recibido una gran atención gracias a sus ventajas únicas en eficiencia energética, tiempo hasta la primera posición (TTFF) y reducidos costes económicos para la implementación. Sin embargo, el estado del arte de los algoritmos relacionados con el posicionamiento de señales instantáneas utilizaron solo medidas de código, lo que inevitablemente limitó la precisión del posicionamiento a al nivel del metro. La presente Tesis Doctoral tiene como objetivo lograr un posicionamiento instantáneo de alta precisión (nivel centimétrico) mediante las medidas de fase de la portadora. Para ello, deben abordarse dos desafíos técnicos antes de que se pueda alcanzar ese nivel de precisión: resolver la inexactitud del tiempo de transmisión del satélite y el llamado problema de ambigüedad de bit de datos (DBA). El primer desafío se origina esencialmente por la falta de precisión de tiempo absoluto en el receptor, ya que solo está disponible la información del tiempo aproximado desde un módulo de asistencia externo y su error puede ser de hasta unos segundos. Así, se propone un método para establecer una etiqueta de tiempo global y construir correspondientemente los pseudorangos con correcciones de período completo. El segundo desafío se debe al hecho de que las mediciones instantáneas se generan en función de los resultados de la correlación entre la señal recibida y las réplicas locales. Las múltiples réplicas generalmente se producen en el posicionamiento de instantáneas siguiendo la arquitectura de de adquisición de el Múltiples Hipótesis (MH). Por lo tanto, se necesita identificar los códigos secundarios reales o los símbolos de bits de datos codificados en la señal recibida, para resolver el DBA. En particular, cuando la réplica local s, Postprint (published version)

The Tonga volcano eruption at 04:15 UT on 2022-01-15 released enormous amounts of energy into the atmosphere, causing very significant geophysical variations not only in the immediate proximity of the epicenter but also globally across the whole atmosphere. The released energy generates perturbations on the electronic density present on the atmosphere, known as Traveling Ionospheric Disturbances (TIDs), i.e., wave-like propagating irregularities that alter the electron density environment and play an important role spreading radio signals propagating through the ionosphere. Geomagnetic and ionospheric phenomena affect communications, GNSS, and other systems on which our technological society depends. The present final master’s thesis aims to analyse some of the most relevant TIDs characteristics (such as propagation speed, time, etc.) as a function of the distance from the eruption in Global Navigation Satellite System (GNSS) signals. First, evaluate Receiver Independent Exchange Format (RINEX) files, i.e., a data interchange format for raw satellite navigation system data, and then, compute Prefit Residuals, i.e., the input data for the navigation equations. With this data, TIDs will be analysed with a series of indices that sample in post-process the disturbance of the ionosphere, developed by Research group of Astronomy and GEomatics of the Universitat Politecnica de Catalunya (gAGE)., La erupción del volcán Tonga a las 04:15 UT del 15-01-2022 liberó enormes cantidades de energía a la atmósfera, desencadenando variaciones geofísicas muy significativas no solo en la proximidad inmediata del epicentro sino también a nivel mundial en toda la atmósfera. Estas variaciones se conocen como perturbaciones ionosféricas viajeras (TID, por sus si-glas en inglés), es decir, irregularidades de propagación en forma de onda que alteran el entorno de densidad de electrones y desempeñan un papel importante en la propagación de señales de radio que se propagan a través de la ionosfera. Los fenómenos geomagnéticos e ionosféricos afectan a las comunicaciones, GNSS y otros sistemas de los que depende nuestra sociedad tecnológica. La presente tesis final de máster tiene como objetivo analizar algunas de las características más relevantes de los TIDs (como la velocidad de propagación, el tiempo, etc.) en función de la distancia desde la erupción en las señales del Sistema Global de Navegación por Satélite (GNSS). Primero, evaluando los archivos de Receiver Independent Exchange Format (RINEX), es decir, un formato de intercambio de datos para los datos brutos del sistema de navegación por satélite, y luego, calculando los residuos de preajuste, es decir, los datos de entrada para las ecuaciones de navegación. Con estos datos, se analizarán las TIDs con una serie de índices que muestrean en postproceso la perturbación de la ionosfera, desarrollados por el grupo de investigación de Astronomía y GEomática de la Universitat Politecnica de Cata-lunya (gAGE)., Incoming

The Global Navigation Satellite System (GNSS) allows computing the Position, Velocity and Time (PVT) of users equipped with appropriate hardware (i.e. an antenna and a receiver) and software. The latter estimates the PVT from the ranging measurements and ephemeris transmitted by the GNSS satellites in frequencies of the L band. The research group of Astronomy and Geomatics (gAGE) at the Universitat Politecnica de Catalunya (UPC) has been developing the GNSS LABoratory (gLAB) tool suite since 2009, in the context of the European Space Agency (ESA) educational program on satellite navigation (EDUNAV). gLAB is a multi-purpose software capable of determining the PVT in several modes: stand-alone (e.g. as a smartphone or car navigator), differential (e.g. surveying equipment or precise farming), and augmented with integrity (e.g. civil aviation or safety of life applications). gLAB has been designed for two main sets of users and functions. The first one is to educate University students and professionals in the art and science of GNSS data processing. This includes newcomers to the GNSS field that highly appreciate the Graphical User Interface (GUI), the default templates with the necessary configuration or the messages with warnings and errors. The second group of users are those with previous experience on GNSS. Those are interested into a high computation speed, high-accuracy positioning, batch processing and access to the intermediate computation steps. In the present contribution, we present some examples in which gLAB serves as an education platform. The data sets are actual GNSS measurements collected by the publicly available International GNSS Service (IGS), together with other IGS products such as the satellite orbits and clocks broadcast in the navigation message. The proposed methodology and procedures are tailored to understand the effects of different error components in both the Signal in Space (SIS) and the position domain, by activating or deactivating

In this study, we focus on the kinematic precise point positioning (PPP) solutions at high-latitudes during the March 2015 great geomagnetic storm. We aim to discover the mechanism behind the positioning degradation from the perspective of the impacts of the storm-induced ionospheric disturbance on the global navigation satellite system (GNSS) data processing. We observed that the phase scintillation dominated the amplitude scintillation at high-latitudes and the variation pattern of the rate of total electron content index (ROTI) was consistent with that of the phase scintillation during the storm. The kinematic PPP errors at high-latitudes were almost three times larger than those at the middle- and low-latitude, which were accompanied by large ROTI variations. From the perspective of GNSS data processing, the large positioning errors were also found to be related to the large number of satellites experiencing cycle slips (CSs). Based on the lock time from the ionospheric scintillation monitoring receiver, we found that a large amount of the CSs was falsely detected under the conventional threshold of the CS detector. By increasing such threshold, the kinematic positioning accuracy at high-latitudes can be improved to obtain similar magnitude as at middle- and low-latitude. The improved positioning accuracy may suggest that the ionospheric disturbance induced by the geomagnetic storm at high-latitudes has minor effects on triggering the CSs. Therefore, precise positioning can be achieved at high-latitudes under geomagnetic storms, given that the CS problem is well addressed., The study is funded by the National Natural Science Foundation of China (No.42004012, 42004025), the Natural Science Foundation of Shandong Province, China (No.ZR2020QD048), the State Key Laboratory of GeoInformation Engineering (No.SKLGIE2019-Z-2-2), the State Key Laboratory of Geodesy and Earth's Dynamics (No. SKLGED-2021-3-4) and by the project RTI2018-094295-B-I00 funded by the MCIN/AEI 10.13039/501100011033, which is co-funded by the FEDER programme., Peer Reviewed, Postprint (published version)

Recently, the Snapshot Real-Time Kinematic (SRTK) technique was demonstrated, which aims at achieving high accuracy navigation solutions with a very short signal collection. The main challenge in implementing SRTK is the generation of valid carrier-phase measurements, which relies on a data bit ambiguity (DBA) resolution process. For pilot signals, this step is equivalent to the correct selection of secondary code indexes (SCIs) from the ambiguous sets obtained from a multi-hypotheses (MH) acquisition process. Currently, SCI ambiguities are solved independently for each satellite. However, this method is ineffective when the snapshot signal is relatively short. In order to tackle this problem, this article proposes a new method that makes use of assistance data and processes information from all satellites to jointly solve the DBA issue. This new method is shown to be more effective in determining the correct SCI and enabling valid snapshot carrier-phase measurements, largely expanding the scope of high-accuracy snapshot positioning., This research was supported by the Albora Technologies and Universitat Politècnica de Catalunya with industrial PhD grant number DI 082 from the Generalitat de Catalunya and the project RTI2018-094295-B-I00 funded by the MCIN/AEI 10.13039/501100011033 which is co-funded by the FEDER programme. P.C. has been partially supported by the NSF under Awards CNS-1815349 and ECCS-1845833., Peer Reviewed, Postprint (published version)

Several X-class solar flares (SFs) with different intensities and locations on the solar disk occurred in September 2017. Among them, the X9.3 SF on 6 September 2017 was the most intensive SF in the 24th solar cycle. In this study, we investigated and compared the ionospheric response to the different X-class SFs and their impacts on the Global Positioning System (GPS) kinematic precise point positioning (PPP) solutions. We aim to study the mechanism behind the positioning degradation from the perspective of the impacts of the SF-induced ionosphere disturbance on the GPS data processing. By comparing the sudden ionospheric disturbance (SID) induced by the SFs, we observed that the SID is controlled by the intensity, the location, and the duration time of the SF. We found that the SID induced by the SF may deteriorate the cycle slip (CS) detection algorithms seriously. The threshold of the CS detection observables is sensitive to the SID, making the CS easier to be falsely detected. On the other hand, for the SF that occurred during the recovery phase of the geomagnetic storm, as the case of the X8.2 SF, the effects of the SF can reduce the precision of the GPS measurements, thus affecting the positioning accuracy. These mechanisms are essential and significant for the accuracy and stability of the kinematic PPP solution obtained with GPS during the SF events., The study is funded by National Natural Science Foundation of China (Nos. 42004012 and 42004025), Natural Science Foundation of Shandong Province, China (No. ZR2020QD048), State Key Laboratory of Geo-Information Engineering (No. SKLGIE2019-Z-2-2), State Key Laboratory of Geodesy and Earth's Dynamics (No. SKLGED-2021-3-4), and by the project RTI2018-094295-B-I00 funded by the MCIN/AEI 10.13039/501100011033, which is cofunded by the FEDER programme. We appreciate the discussion on the amplitude scintillation and IF-sigma from high-rate geodetic GNSS data with Dr. Xiaomin Luo from China University of Geosciences (Wuhan) and Prof. Juan, J. M. from Universitat Politecnica de Catalunya (UPC), Spain. The authors are also thankful to the reviewers for the instructive comments and suggestions on the manuscript., Peer Reviewed, Postprint (published version)

We focus on the impacts of the polar cap ionospheric sporadic-E (Es) layer that occurred at Resolute Bay, Canada, on September 5, 2012, on the quality of the Global Positioning System (GPS) observable and the positioning performance. Mainly, we are concerned about the relationship between the thin Es layer and the ionosphere scintillation and the reason behind the degraded positioning performance during the event of the polar cap Es. The results show that the polar cap Es can trigger weak-to-moderate amplitude scintillation and the maximum positioning errors in the up component for the Ionospheric-Free Precise Point Positioning (IF-PPP) model can reach up to 0.51 m while that for the Uncombined PPP (UC-PPP) model can reach 1.20 m. The maximum positioning errors occur simultaneously with the time of the maximum amplitude scintillation induced by the polar cap Es. The degraded positioning performance can be attributed mostly to falsely detected cycle slips (CSs), which are influenced by the polar cap Es layer-induced scintillation. To mitigate this, we propose the 3-sigma rule to determine the threshold of the CS detection observables. The preliminary results show that compared with the commonly adopted threshold values, the positioning accuracy improvement in the up component is 14.1% for the IF-PPP model while the corresponding improvement is 40.8% for the UC-PPP model, suggesting that the high accuracy positioning performance can be achieved in the high latitude region by statistic characterization of the CS thresholds., The study is funded by the National Natural Science Foundation of China (No.42004012, 42004025), Natural Science Foundation of Shandong Province, China(No.ZR2020QD048),State Key Laboratory of Geo-Information Engineering (No.SKLGIE2019-Z-2-2), State Key Laboratory of Geodesy and Earth Dynamics (No. SKLGED-2021-3-4) and by the project RTI2018-094295-B-I00 funded by the MCIN/AEI 10.13039/501100011033 which is co-founded by the FEDER program. We acknowledge the usage of the GAMP package for the positioning performances at https://www.ngs.noaa.gov/gps-toolbox/. We thank the anonymous reviewers and Editors for the comments and suggestions, which significantly improve the quality of the manuscript., Peer Reviewed, Postprint (published version)

With great potential for being applied to Internet of Things (IoT) applications, the concept of cloud-based Snapshot Real Time Kinematics (SRTK) was proposed and its feasibility under zero-baseline configuration was confirmed recently by the authors. This article first introduces the general workflow of the SRTK engine, as well as a discussion on the challenges of achieving an SRTK fix using actual snapshot data. This work also describes a novel solution to ensure a nanosecond level absolute timing accuracy in order to compute highly precise satellite coordinates, which is required for SRTK. Parameters such as signal bandwidth, integration time and baseline distances have an impact on the SRTK performance. To characterize this impact, different combinations of these settings are analyzed through experimental tests. The results show that the use of higher signal bandwidths and longer integration times result in higher SRTK fix rates, while the more significant impact on the performance comes from the baseline distance. The results also show that the SRTK fix rate can reach more than 93% by using snapshots with a data size as small as 255 kB. The positioning accuracy is at centimeter level when phase ambiguities are resolved at a baseline distance less or equal to 15 km., This research was funded by Albora Technologies and Universitat Politècnica de Catalunya with industrial PhD grant number DI 082 from the Generalitat de Catalunya; This research was partially funded by the Spanish Ministry of Science and Innovation project RTI2018-094295-B-I00. P.C. has been partially supported by the NSF under Awards CNS-1815349 and ECCS-1845833, Peer Reviewed, Postprint (published version)

Satellite navigation systems require of knowing satellite positions with a high level of accuracy. Unlike other GNSS constellations, GLONASS ephemeris can not be directly obtained from broadcast navigation messages at any desired epoch. A data post process is required to compute the user solution. The present MSc thesis focuses on implementing an algorithm to compute GLONASS coordinates and clocks at any epoch from the broadcast navigation message and allows its accuracy assessment and error characterization, with respect to precise products. Analyzing the resulting data provides values of coordinate and clock differences for short and long terms. The error characterization procedures give a comparison between different GLONASS satellites, allowing to obtain best and worst cases in relation to their coordinates and clock offsets accuracy.

Scintillation is a particular type of space weather disturbance that currently limits the accuracy and availability of the Global Navigation Satellite System. The present final master’s thesis aims to study the characteristics of satellite navigation techniques. First, evaluate the impact of scintillation on the frequencies and signals used in space-based navigation systems. For this, the TFM will make use of the Geodetic Detrending technique developed by research group Astronomy and Geomatics of the Universitat Politecnica de Catalunya (gAGE). The final objective of this TFM is to show that, once the scintillation effect has been detected, there are receptors that in combination with certain signals can influence navigation or the study of the atmosphere.

The space segment of the Global Navigation Satellite System (GNSS) is equipped with highly stable atomic clocks. In order to use these clocks as references, their time offsets must be estimated from ground measurements as accurately as possible. This work presents a multi-frequency and multi-constellation method for estimating satellite and receiver clock corrections, starting from unambiguous, uncombined, and undifferenced carrier-phase measurements. A byproduct of the estimation process is phase biases (i.e., the hardware delays of the carrier-phase measurements occurring at receivers and satellites). The stability and predictability of our clock estimates for receivers and satellites (GPS and Galileo) are compared with those obtained by the International GNSS Service (IGS), whereas the phase biases are assessed against two independent determinations involving combinations of carrier-phase measurements. We conclude that the method reduces day boundary discontinuities in the clock corrections, and that the estimated phase biases reproduce variabilities already observed by other authors., The present work was supported in part by the Euro-pean Space Agency contract (REL-GAL) N.4000122402/17/NL/IB, by the project RTI2018-094295-B-I00 funded bytheMCIN/AEI10.13039/501100011033whichisco-foundedby the FEDER programme, and by the Horizon 2020 MarieSkłodowska-Curie Individual Global Fellowship 797461NAVSCIN. The authors acknowledge the use of data andproducts provided by the International GNSS Service, Peer Reviewed, Postprint (published version)

The GNSS LABoratory tool (gLAB) is an interactive educational suite of applications for processing data from the Global Navigation Satellite System (GNSS). gLAB is composed of several data analysis modules that compute the solution of the problem of determining a position by means of GNSS measurements. The present work aimed to improve the pre-fit outlier detection function of gLAB since outliers, if undetected, deteriorate the obtained position coordinates. The methodology exploits robust statistical tools for regression provided by the Flexible Statistics and Data Analysis (FSDA) toolbox, an extension of MATLAB for the analysis of complex datasets. Our results show how the robust analysis FSDA technique improves the capability of detecting actual outliers in GNSS measurements, with respect to the present gLAB pre-fit outlier detection function. This study concludes that robust statistical analysis techniques, when applied to the pre-fit layer of gLAB, improve the overall reliability and accuracy of the positioning solution., This work was supported in part by the Spanish Ministry of Science, Innovation and Universities project RTI2018-094295-B-I00 and in part by the Horizon 2020 Marie Skłodowska-Curie Individual Global Fellowship 797461 NAVSCIN., Peer Reviewed, Postprint (published version)

Global navigation satellite system (GNSS) satellites are equipped with very stable atomic clocks that can be used for assess-ing the models and strategies involved in the estimation processes, where the clock estimates should present high stability. For instance, GNSS products (including satellite and receiver clocks) are computed on daily basis, i.e., with the data of each day being processed independently from other days. This choice produces the well-known day-boundary discontinuities (DBDs) on clock estimates that stem from the estimation process, rather than to the nature of the atomic clock itself. The aim of the present contribution is to propose a strategy to estimate the satellite and receiver clock offsets that is capable to reduce the DBDs observed in the products of different analysis centers (ACs) within the International GNSS Service (IGS), ultimately improving the accuracy of clock estimates. Our approach relies on the use of unambiguous, undifferenced and uncombined carrier phase measurements collected by a network of permanent receivers on ground. The strategy consid-ers the carrier phase hardware delays and assumes their possible variations along time. Our daily data processing aims to maintaining the natural continuity over days of the carrier phase measurements after integer ambiguity resolution (IAR), even if IAR is performed on daily batches. We compare our clock estimations with those computed by different IGS ACs, evaluating the linear behavior of the satellite atomic clocks on the day change. The results show the removal of DBD on clock estimates computed with the continuous and unambiguous carrier phase measurements. This DBD improvement may benefit the statistical characterization of long-term phenomena correlated with the on-board clocks., The present work was supported in part by the European Space Agency contract (REL-GAL) N.4000122402/17/NL/IB, by the Spanish Ministry of Science, Innovation and Universities project RTI2018-094295-B-I00 and by the Horizon 2020 Marie Skłodowska-Curie Individual Global Fellowship 797461 NAVSCIN. The authors acknowledge the use of data and products provided by the International GNSS Service, Peer Reviewed, Postprint (published version)

Users of the global navigation satellite system (GNSS) operating with a single-frequencyreceiver must use an ionospheric correction algorithm (ICA) to account for the delay introduced onradio waves by the upper atmosphere. Galileo, the European GNSS, uses an ICA named NeQuick-G. In an effort to foster the adoption of NeQuick-G by final users, two implementations in Clanguage have been recently made available to the public by the European Space Agency (ESA)and the Joint Research Centre (JRC) of the European Commission (EC), respectively. The aim ofthe present contribution is to compare the slant total electron content (STEC) predictions of thetwo aforementioned implementations of NeQuick-G. For this purpose, we have used actual multi-constellation and multi-frequency data for several hundreds of stations distributed worldwidebelonging to the Multi GNSS Experiment (MGEX) network of the International GNSS Service (IGS).For each first day of the month during year 2019, the STECs of the two NeQuick-G versions werecompared in terms of accuracy, consistency, availability, and execution time. Our study concludesthat both implementations of NeQuick-G perform equivalently. Indeed, in over 99.998% of the 2125million STECs computed, the output is exactly coincident. In contrast, 0.002% of the whole set ofSTECs for those rays are tangent to the Earth, the behavior of both implementations differs. Weconfirmed the discrepancy by processing radio-occultation actual measurements from a COSMIC-2 low Earth orbit satellite. We selected the JRC version of the Galileo ICA to be integrated intothe GNSS LABoratory (gLAB) tool suite, because its open license and its processing speed (it is13.88% faster than the ESA version). NeQuick-G outperforms the GPS ICA in STEC residuals up to12.15 TECUs (percentile 96.23th) and in the 3D position errors, up to 5.76 m (percentile 99.18th) forcode-pseudorange positioning., This work was supported in part by the Spanish Ministry of Science, Innovation andUniversities project RTI2018-094295-B-I00 and in part by the Horizon 2020 Marie Skłodowska-Curie Individual Global Fellowship 797461 NAVSCIN., Peer Reviewed, Postprint (published version)

The Galileo High Accuracy Service (HAS) is a new capability of the European Global Navigation Satellite System that is currently under development. The Galileo HAS will start providing satellite orbit and clock corrections (i.e. non-dispersive effects) and soon it will also correct dispersive effects such as inter-frequency biases and, in its full capability, ionospheric delay. We analyse here an ionospheric correction system based on the fast precise point positioning (Fast-PPP) and its potential application to the Galileo HAS. The aim of this contribution is to present some recent upgrades to the Fast-PPP model, with the emphasis on the model geometry and the data used. The results show the benefits of integer ambiguity resolution to obtain unambiguous carrier phase measurements as input to compute the Fast-PPP model. Seven permanent stations are used to assess the errors of the Fast-PPP ionospheric corrections, with baseline distances ranging from 100 to 1000 km from the reference receivers used to compute the Fast-PPP corrections. The 99% of the GPS and Galileo errors in well-sounded areas and in mid-latitude stations are below one total electron content unit. In addition, large errors are bounded by the error prediction of the Fast-PPP model, in the form of the variance of the estimation of the ionospheric corrections. Therefore, we conclude that Fast-PPP is able to provide ionospheric corrections with the required ionospheric accuracy, and realistic confidence bounds, for the Galileo HAS., Open Access funding provided thanks to the CRUECSIC agreement with Springer Nature. The present work was supported in part by the European Space Agency contract IONO4HAS 4000128823/19/NL/AS, by the project RTI2018-094295-B-I00 funded by the MCIN/AEI 10.13039/501100011033 which is co-founded by the FEDER programme and by the Horizon 2020 Marie Skłodowska-Curie Individual Global Fellowship 797461 NAVSCIN., Peer Reviewed, Postprint (published version)

Scintillation is a particular type of space weather perturbation occurred when the signals from the Global Navigation Satellite System (GNSS) traverse irregularities in the ionosphere; the upper layer of the Earth atmosphere. This produces rapid variations on the refraction index and, when the size of the irregularities is close to the Fresnel length of the frequencies used in GNSS frequencies, can also produce diffractive effects affecting the signal amplitude and the tracking of the carrier-phase measurements. Under these conditions, techniques delivering a High Accuracy Service (HAS) are severely degraded in terms of positioning accuracy and availability. The research group of Astronomy and Geomatics has recently introduced the Geodetic Detrending to perform scintillation studies. The GD method removes slowly-varying effects (i.e., trends) in the GNSS signals, such as the satellite movement, the on-board atomic clock offset, and the tropospheric delay (the atmosphere layer from sea level up to 50 km in height). Once the trends are removed, the GD technique allows studying effects of shorter time-scale –rapid fluctuations–of the GNSS signals, with the focus on the identification and correction of discontinuities, the so-called “cycle-slips”, on the geodetically de-trended GNSS carrier-phase measurements. Ultimately, once the cycle-slips problem is mitigated, the HAS can be re-stored under scintillation conditions., The authors acknowledge the use of data and products provided by the International GNSS Service., Postprint (published version)

Global Navigation Satellite System (GNSS) data can be used in a myriad of ways. The current number of applications exceed by far those originally GNSS was designed for. As an example, the present Special Issue on GNSS Data Processing and Navigation compiles 14 international contributions covering several aspects of GNSS research. This Editorial summarizes the whole special issue grouping the contributions under four different, but related topics, Adria Rovira Garcia is a Serra Hunter Lecturer and presently holds a Marie Sklodowska Curie IndividualFellowship titled “High Accuracy Navigation under Scintillation Conditions (NAVSCIN)”, Postprint (published version)

The present contribution evaluates how the European Geostationary Navigation Overlay System (EGNOS) meets the International Maritime Organization (IMO) requirements established in its Resolution A.1046 for navigation in harbor entrances, harbor approaches, and coastal waters: 99.8% of signal availability, 99.8% of service availability, 99.97% of service continuity and 10 m of horizontal accuracy. The data campaign comprises two years of data, from 1 May 2016 to 30 April 2018 (i.e., 730 days), involving 108 permanent stations located within 20 km of the coast or in islands across the EGNOS coverage area, EGNOS corrections, and cleansed GPS broadcast navigation data files. We used the GNSS Laboratory Tool Suite (gLAB) to compute the reference coordinates of the stations, the EGNOS solution, as well as the EGNOS service maps. Our results show a signal availability of 99.999%, a horizontal accuracy of 0.91 m at the 95th percentile, and the regions where the IMO requirements on service availability and service continuity are met. In light of the results presented in the paper, the authors suggest the revision of the assumptions made in the EGNOS Maritime Service against those made in EGNOS for civil aviation; in particular, the use of the EGNOS Message Type 10., This research was funded by the European GNSS Agency within the framework Integration of the Fundamental Elements, Contract GSA/OP/12/16/Lot1/SC1, and the APC was funded by the Spanish Ministry of Science, Innovation and Universities Project RTI2018-094295-B-I00., Peer Reviewed, Postprint (published version)

Single-frequency users of the global navigation satellite system (GNSS) must correct for the ionospheric delay. These corrections are available from global ionospheric models (GIMs). Therefore, the accuracy of the GIM is important because the unmodeled or incorrectly part of ionospheric delay contributes to the positioning error of GNSS-based positioning. However, the positioning error of receivers located at known coordinates can be used to infer the accuracy of GIMs in a simple manner. This is why assessment of GIMs by means of the position domain is often used as an alternative to assessments in the ionospheric delay domain. The latter method requires accurate reference ionospheric values obtained from a network solution and complex geodetic modeling. However, evaluations using the positioning error method present several difficulties, as evidenced in recent works, that can lead to inconsistent results compared to the tests using the ionospheric delay domain. We analyze the reasons why such inconsistencies occur, applying both methodologies. We have computed the position of 34 permanent stations for the entire year of 2014 within the last Solar Maximum. The positioning tests have been done using code pseudoranges and carrier-phase leveled (CCL) measurements. We identify the error sources that make it difficult to distinguish the part of the positioning error that is attributable to the ionospheric correction: the measurement noise, pseudorange multipath, evaluation metric, and outliers. Once these error sources are considered, we obtain equivalent results to those found in the ionospheric delay domain assessments. Accurate GIMs can provide single-frequency navigation positioning at the decimeter level using CCL measurements and better positions than those obtained using the dual-frequency ionospheric-free combination of pseudoranges. Finally, some recommendations are provided for further studies of ionospheric models using the position domain method., Peer Reviewed, Postprint (published version)

A preliminary analysis of Galileo F/NAV broadcast Clock and Ephemeris is performed in this paper with 43 months of data. Using consolidated Galileo Receiver Independent Exchange (RINEX) navigation files, automated navigation data monitoring is applied from 1 January 2017 to 31 July 2020 to detect and verify potential faults in the satellite broadcast navigation data. Based on these observation results, the Galileo Signal-in-Space is assessed, and the probability of satellite failure is estimated. The Galileo nominal ranging accuracy is also characterized. Results for GPS satellites are included in the paper to compare Galileo performances with a consolidated constellation. Although this study is limited by the short observation period available, the analysis over the last three-year window shows promising results with Psat= 3.2 × 10-6/sat, which is below the value of 1 × 10-5 stated by the Galileo commitment, This research was funded by the ESA contract 4000118045/16/NL/WE and by the Spanish Ministry of Science and Innovation project RTI2018-094295-B-I00., Postprint (published version)

As the world becomes more complex rapidly having a smart infrastructure is a necessity to be able to manage them remotely by high accuracy. In order to cope with this issue we need to have precise navigation globally which could be challenging in high- and low latitudes then the focus here is on six GNSS (Global Navigation Satellite System) receivers in the arctic region (high latitude) with GLONASS and GPS constellations. The impact of ionospheric scintillation has been characterized based on Sigma Phi, AATR and ROTI, using a database of one year of data in 2014. The thresholds from cumulative distribution function (CDF) of those scintillation parameters at 99% and 99.9% for each station per constellation have been extracted and high scintillation events were detected. The 1-CDF plots of December and July were compared and the seasonal Sigma Phi evolution has been analyzed for different stations per constellation. Moreover the linear correlation between ROTI and Sigma Phi was observed. These correlation indexes highly depend on type of the receiver, location of the receiver and the type of constellation used which will help us to differentiate between the level or impact of scintillation measured for different receivers per constellation. The scintillation events are observed to depend generally on the location of the receiver, period of the day, performance of the receiver, satellite constellation, and ionosphere behaviour. In addition, the impact of data loss in the database analysed has been shown to be relevant and different from station to station. Finally, single frequency PPP could have a higher convergence time in comparison with double frequency PPP according to a preliminary study. Hence, a detailed future work to investigate this issue is proposed.

Time synchronization is one of the main applications of Global Navigation Satellite System (GNSS). Indeed, GNSS satellites are equipped with highly stable atomic clocks, which can be used as clock references. In particular, Galileo constellation satellites are equipped with Rubidium and Hydrogen-maser frequency standards that have a long-term (1-day) stability at the level of 10-14 for intervals of 104 s. However, in order to use these clocks as references, their time offsets must be estimated from measurements collected on ground. In this sense, the effectiveness of these references depends on the accuracy and stability of such estimates. For that reason, the International GNSS Service (IGS) is providing satellite solutions with a nominal accuracy of 75 ps (i.e. better than 3 cm). The clock accuracy is assessed by evaluating the discontinuities over consecutive days, computed independently. These discontinuities appear because of the correlations between the different parameters, which are estimated jointly with the satellite clocks (e.g. receiver clocks or carrier phase ambiguities). Therefore, satellite clocks depend on the robustness of the different models used in the estimation process. For the Galileo satellites, the inter-day discontinuities are at the level of 0.5 ns. These large jumps are due to the minor number of Galileo satellites available than in GPS, which results in a reduced number of fixed carrier phase ambiguities (other solutions from other IGS analysis centers present similar features). In this work we present a refinement of the method for estimating satellite and receiver clocks, which is able to reduce these discontinuities and, consequently, to improve the accuracy of the satellite clock estimations (according to the above-mentioned IGS metric applied). Some of the main characteristics of this new approach are 1) the use of unambiguous carrier phases, 2) processing several constellations and several frequencies and 3) considering the temper, Postprint (published version)

Signals from a Global Navigation Satellite System (GNSS) can be disturbed along the propagation ray path from the satellites to the receivers. The presence of irregularities in the electron density in the near-Earth space environment can cause refraction and/or diffraction in the electromagnetic signals used by GNSS. This causes fast fluctuations of the GNSS signals known as scintillation. Currently, specialized Ionospheric Scintillation Monitoring Receivers (ISMRs) are used to characterize the intensity (or amplitude) and the phase scintillation. ISMRS are capable of sampling GNSS carrier-phase measurements at high-rate (e.g. 50 to 100 Hz) and must be equipped with a highly stable clock. In contrast, the present contribution studies the climatology of scintillation at high- and low- latitudes for both hemispheres and for a long temporal series, with measurements gathered by conventional geodetic receivers with a sampling frequency of 1 Hz that belong to the International GNSS Service (IGS) network. The derivation of S4 (amplitude scintillation) and ?? (phase scintillation) parameters uses a novel technique based in a precise Geodetic Detrending (GD) of the carrier-phase measurements, as in Precise Point Positioning (PPP). Amplitude and phase scintillation have been statistically characterized by means of the cumulative distribution functions (CDF) of S4 and ?? parameters. The thresholds for moderate and intense scintillation periods are established from the 99% and 99.9% percentiles of the CDFs as 0.25 and 0.45 for ?? values and 0.3 and 0.5 for S4 values, respectively. The large temporal series analyzed allows relating high-activity periods to severe space weather events such as geomagnetic storms at high-latitudes, to local times from 19h to midnight at low-latitudes and studying the seasonal dependencies. We conclude that the GD method is a powerful tool to perform scintillation studies and that it can be applied to individual (i.e. uncombined) signal frequencies, The authors acknowledge the use of data and products provided by the International GNSS Service. Data from the Ionospheric Monitoring Experimentation Plan and Instrument Development (MONITOR) from the European Space Agency (ESA) has been used. The research reported in this paper was financially supported in part by the ESA under contract 4000120868/17/NL/AF and in part by the Spanish Ministry of Science, Innovation and Universities project RTI2018-094295-B-I00 belonging to the RETOS 2018 call., Peer Reviewed, Postprint (published version)

Users of the Global Navigation Satellite System (GNSS) using a single-frequency receiver need to use an Ionospheric Correction Algorithm (ICA) to compensate the delay introduced by the Ionosphere on radio waves. The European GNSS, Galileo, uses an ICA named NeQuick-G since it is an adaptation to real time use of the 3D climatological model NeQuick, whereas the American Global Positioning Service (GPS) uses the Klobuchar ICA, which was also adopted initially by the Chinese GNSS, Beidou. In an effort to foster the adoption of NeQuick-G by final users, two implementations in C language were made publicly available by the European Space Agency (ESA) and the Joint Research Centre (JRC) of the European Commission (EC) respectively. The latter, was chosen to be integrated in the GNSS laboratory tool suite (gLAB), developed by the research group of Astronomy and Geomatics (gAGE) of the Universitat Politecnica de Catalunya (UPC) because its open license and its processing speed. The aim of the present contribution is to compare the Slant Total Electron Content (STEC) predictions of the two aforementioned ICAs and assess their differences in the navigation domain using the gLAB tool. For this purpose, we have used multi-frequency data for several hundreds of stations distributed worldwide belonging to the International GNSS Service (IGS) network. For each first day of the month during year 2019, the outcomes STECs of the two ICAs have been compared in terms of accuracy, availability and execution time. For completeness and inter-comparisons, STEC from post-processed Global Ionospheric Maps from IGS have been also been accounted for. Then, for each station involved in the experiment, positioning errors have been analyzed while using the different ionospheric corrections., The authors acknowledge the use of data and products provided by the International GNSS Service. The research reported in this paper has been partially supported by the Horizon 2020 Marie Skłodowska-Curie Individual Global Fellowship 797461 NAVSCIN and by the Spanish Ministry of Science, Innovation and Universities project RTI2018-094295-B-I00 a., Peer Reviewed, Postprint (published version)

With snapshot positioning becoming popular for various applications, the present contribution focuses on the feasibility of achieving Real Time Kinematics (RTK) positioning using snapshot data, i.e. a very brief interval of the received satellite signal. This method is termed as Snapshot RTK (SRTK). We first introduce the general workflow of snapshot positioning and the SRTK engine functioning blocks. Their differences from traditional receivers and challenges brought by the short duration of data are explained. Since a major difference of this positioning method is the generation of code and carrier-phase GNSS observables, we go through this procedure in details. In order to explore the feasibility of achieving RTK under different scenarios, the rate of Integer Ambiguity Resolution (IAR) is assessed by using snapshot measurements generated with different integration times and signal bandwidths under zero-baseline configuration. Under these assumptions, the key factor that influences the RTK fix rate is the code measurement noise. Double Difference (DD) code measurement errors are evaluated and plotted together with the resulting IAR fix rates in order to find the relationship between them. The performance of using multi-constellation and multi-frequency signals is tested as well. The fix rate can reach 100% when multiple constellations are used. The achieved positioning accuracy is shown to be less than 5 mm in horizontal domain when IAR is achieved successfully. Finally, some conclusions and thoughts about future research steps on SRTK are given., The author would like to acknowledge Albora Technologies for the technical support during the whole course of this research, including collection of raw data and developments of related software and libraries. The authors would like to thank Everis Aeroespacial y Defensa, S.L.U. for lending the Septentrio base station receiver for this research. The research reported in this paper has been partially supported by the Doctorat Industrial Grant 2018 DI 082 from the Generalitat de Catalunya, and the Spanish Ministry of Science, Innovation and Universities project RTI2018- 094295-B-I00. P. Closas was partially supported by the National Science Foundation under Awards CNS-1815349 and ECCS-1845833., Peer Reviewed, Postprint (published version)

Medium-scale traveling ionospheric disturbances (MSTIDs) are fluctuations in the plasma density that propagate through the upper layer of the atmosphere at velocities of approximately 100 m/s and periods reaching some tens of minutes. Due to their wavelengths, MSTIDs can degrade the performance of differential positioning techniques, such as real-time kinematics (RTK) or network-RTK (NRTK). This paper defines a novel methodology as a tool for relating the errors in NRTK positioning based on an MSTIDs indicator using the second difference in time of the slant total electron content (STEC). The pro-posed methodology performs integer ambiguity resolution (IAR) on the undifferenced measurements instead of using double-differenced carrier-phase measurements, as it is usual in RTK and NRTK. Statistical tests are applied to evaluate the degradation in the position errors caused by the impacts of MSTIDs on RTK and NRTK positioning over a data set spanning one year gathered from the CATNET network; a dual-frequency network of fixed permanent GNSS receivers located at the mid-latitudes of northeastern Spain. With the development of the proposed methodology for measuring the position degradation, another results of the present research are the establishment of thresholds for the proposed MSTIDs index, which can be used to monitor the positioning solution and to warn users when the measurements are affected by MSTIDs events, relating the position error to MSTIDs that affect not only the user receivers but also of the reference receivers within the network., Peer Reviewed, Postprint (published version)

The Multi-constellation Global Navigation Satellite System (Multi-GNSS) has become the standard implementation of high accuracy positioning and navigation applications. It is well known that the noise of code and phase measurements depend on GNSS constellation. Then, Helmert variance component estimation (HVCE) is usually used to adjust the contributions of di¿erent GNSS constellations by determining their individual variances of unit weight. However, HVCE requires a heavy computation load. In this study, the HVCE posterior weighting was employed to carry out a kinematic relative Multi-GNSS positioning experiment with six short-baselines from day of year (DoY) 171 to 200 in 2019. As a result, the HVCE posterior weighting strategy improved Multi-GNSS positioning accuracy by 20.5%, 15.7% and 13.2% ineast-north-up(ENU) components, compared to an elevation-dependent (ED) priori weighting strategy. We observed that the weight proportion of both code and phase observations for each GNSS constellation were consistent during the entire 30 days, which indicates that the weight proportions of both code and phase observations are stable over a long period of time. It was also found that the quality of a phase observation is almost equivalent in each baseline and GNSS constellation, whereas that of a code observation is different. In order to reduce the time consumption off the HVCE method without sacrificing positioning accuracy, the stable variances of unit weights of both phase and code observations obtained over 30 days were averaged and then frozen as a priori information in the positioning experiment. The result demonstrated similar ENU improvements of 20.0%, 14.1% and 11.1% with respect to the ED method but saving 88% of the computation time of the HCVE strategy. Our study concludes with the observations that the frozen variances of unit weight (FVUW) could be applied to the positioning experiment for the next 30 days, that is, from DoY 201 to 230 in 2019, improving the, Peer Reviewed, Postprint (published version)