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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)

This final degree project focuses on the development of a GNSS (Global Navigation Satellite System) receiver block, based on a radiofrequency switching matrix. The main objective is to take the first step towards the operability of the satellite navigation system and the receiver for reflectometry and radio occultation experiments. This project is carried out in collaboration with UPC NanoSat Lab, a department of the Universitat Politècnica de Catalunya specialized in launching nanosatellites for earth observation. Specifically, within the framework of the 3CAT-8 mission, the phenomenon of ionospheric scintillation is being investigated, that is, how radiofrequency waves are affected when crossing the ionosphere. Additionally, it aims to monitor radio frequency interference (RFI) in the L and K frequency bands as a secondary objective. This project involves a deep theoretical study on GNSS concepts and their implications in reflectometry and radio occultation fields. Next, the different subsystems of the satellite are thoroughly explored for the generation of a comprehensive design that will integrate existing antennas with receivers, considering the scientific requirements of the mission and selecting components according to space standards. Furthermore, the necessary printed circuit boards are developed for efficient integration of the switching matrix with the rest of the satellite subsystems, always respecting the basic characteristics of GNSS signals and their fundamental properties. This project represents the first step towards the culmination of the satellite system responsible for conducting the scientific tests of the 3CAT-8 mission.

El present treball de fi de grau avalua els diferents tipus sistemes GNSS, determinant els components essencials que han d'adquirir-se per a aconseguir un sistema funcional. S'analitzaran les diferents constel·lacions determinant si és millor utilitzar un únic sistema com podria ser el GPS o el Galileu o si seria més eficient utilitzar la combinació de diferents constel·lacions de satèl·lits. El projecte es realitza sota la supervisió i suport dels membres del CDEI-UPC amb els quals es treballarà conjuntament per a definir i aconseguir els reptes proposats. Una vegada determinat quals són els components necessaris, es formalitzaran reunions amb diferents proveïdors de sistemes GNSS per a triar el sistema que compleixi amb el major nombre d'especificacions i objectius que es proposen durant el treball i es testessin els sistemes triats per a així prendre decisions basats en les dades reals comprades amb teòrics proporcionats pels fabricants. Per últim, s'analitzarà la viabilitat de la integració del sistema triat en el robot mitjançant l'ús del llenguatge ROS per a així en les següents fases del projecte dur a terme la integració física del sistema, El presente trabajo de fin de grado evalúa los diferentes tipos sistemas GNSS determinando los componentes esenciales que deben adquirirse para conseguir un sistema funcional. Se analizarán las diferentes constelaciones determinando si es mejor utilizar un único sistema como podría ser el GPS o el Galileo o si sería más eficiente utilizar la combinación de diferentes constelaciones de satélites. El proyecto se realiza bajo la supervisión y soporte de los miembros del CDEI-UPC con los cuales se trabajará conjuntamente para definir y conseguir los retos propuestos. Una vez determinado cuales son los componentes necesarios, se formalizarán reuniones con diferentes proveedores de sistemas GNSS para escoger el sistema que cumpla con el mayor número de especificaciones y objetivos que se proponen durante el trabajo y se testearan los sistemas escogidos para así tomar decisiones basados en los datos reales comprados con los teóricos proporcionados por los fabricantes. Por último, se analizará la viabilidad de la integración del sistema escogido en el robot mediante el uso del sistema operativo ROS para así en las siguientes fases del proyecto llevar a cabo la integración física del sistema, This thesis evaluates the different types of GNSS systems by determining the essential components that must be acquired to achieve a functional system. The different constellations will be analysed to determine if it is better to use a single system such as GPS or Galileo or if it would be more efficient to use a combination of different satellite constellations. The project is carried out under the supervision and support of the members of the CDEI- UPC with whom I will work together to define and achieve the proposed challenges. Once the necessary components are determined, meetings will be formalized with different GNSS system providers to choose the system that meets the highest number of specifications and objectives proposed during the work, the chosen systems will be tested in order to make decisions based on the real data purchased with the theoretical data provided by the manufacturers. Finally, the feasibility of the integration of the chosen system in the robot will be analysed through the use of the ROS language to carry out the physical integration of the system in the following phases of the project.

This project combines GNSS-R technology and UAVs in the context of the aerial remote sensing field, from the design of the assembly of the UAVs and GNSS-R to the execution of the different tests, as well as the data collection and analysis. As it will be seen in the document, this analysis has allowed to improve the original design of the system. The remote sensing technology based on GNSS reflected signals is simply called GNSS-R, and the greatest advantage of UAV as a mounting platform is the low cost, high system availability, and fast installation. Thus the main task of this project is to experimentally verify the possibility of CTTC's own developed GNSS-R working with UAVs. In this report, first I explain some basic principles of GNSS and GNSS-R, as they are important technical backgrounds for the whole project. Secondly, I describe the application of the RTKPOST software, which is an important processing and analyzing tool in the entire project, mainly describing the positioning methods used in the different processing modes in RTKPOST, also the parameter needed for analysis. Then, the design of the UAV-GNSS-R assembly is discussed, with different options based on the characteristics of the UAV, such as weight, payload space, and so on. The whole experimental process is also explained, and all the test data are analyzed and processed by using the Static mode or Kinematic mode in RTKPOST, and the data results are analyzed and compared in terms of satellite visibility, signal-to-noise ratio, elevation angle, Standard Deviation and Root Mean Square. The experimental process is roughly divided into three parts. The initial verification test is used to collect signal data as a basis, through which it is found that drone interferes with GNSS-R to a greater extent, and that the reflector antenna cannot receive the signal if the drone is placed too close to the ground. The second part of the experiment is a stationary test, where the UAV is placed on a tripod, and it', Objectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats Sostenibles

This paper proposes a proper compass adjustment method using only a GPS (or any other GNSS receiver) and a single visual reference to enhance the efficiency of compass adjustment. During compass adjustment, the ship proceeds on magnetic courses using a gyroscopic or satellite compass and considering magnetic declination. However, non-magnetic compasses are only compulsory for ships of 500 gross tonnage or upwards (SOLAS V/19.2.5.1). Many ships of less than 500 gross tonnage have only a magnetic compass to indicate heading. In these cases, a minimum of five leading lines or a minimum of five bearings of conspicuous and distant points or sun azimuths are necessary to adjust the compass. This makes compass adjustment more laborious and time consuming. To expedite this process, a reliable and practical method was developed to use the courses over ground given by a GNSS receiver and a single visual reference instead of the headings provided by a gyroscopic or satellite compass. The method is valid for all ships, but is primarily intended for those equipped with only a magnetic compass to indicate heading., Postprint (author's final draft)

Certified Ground Based Augmentation Systems (GBAS) as of today operate using only GPS signals in the L1 frequency band to enable precision approach guidance for landing aircraft. Ionospheric activity (i.e., scintillations and/or large abnormal ionospheric gradients) is a major limitation for the availability of current GBAS services, especially in equatorial and polar regions. To overcome these availability limitations, current developments aim at extending GBAS to the use of dual-frequency and multi-constellation (DFMC) techniques. Using signals on a second frequency, in this case L5/E5a, allows for a less conservative ionospheric monitoring, improving the availability of GBAS in regions with high ionospheric activity. In previous work, we proposed an airborne ionospheric gradient monitoring concept to detect significant ionospheric delay differences between a GBAS ground station and an airborne user. This concept was initially developed for the assumption of a single satellite affected by an ionospheric gradient. While extending it for case with multiple satellites simultaneously affected, the proposed monitoring thresholds were getting extremely sensitive with a consequent raise of the false alarm probability of the monitor. Furthermore, the concurrent impact of an ionospheric gradient on multiple satellites could deteriorate the monitoring performance, and thus the detectability. In this work, we revisit the previously proposed monitoring scheme to improve its robustness, especially in the situation when several satellites are affected simultaneously. This is achieved through a median removal step, which makes the quantities derived from the pseudorange corrections from the ground station and the ionospheric delay estimates derived from dual-frequency pseudorange measurements from the aircraft comparable without adding a bias to the unaffected satellites. In addition, we propose a method to monitor all satellites currently in use at once, avoiding the need to ma, The authors would like to thank INDRA Satnav and Telespazio for providing the simulated nominal data in the frame of the European project SESAR 2020 PJ14-03-01, Peer Reviewed, Postprint (author's final draft)

El projecte descrit en aquest document es centra en el posicionament de precisió a partir de les mesures de fase dels senyals provinents dels satel·lits GNSS (Global Navigation Satellite System). A partir d’un receptor NEO-7P es busquen tecniques que permetin fer ús d’aquest concepte i aconseguir posicionaments amb errors reduïts, per tal de ser utilitzats en la navegacio aèria, tot i les limitacions que disposa el hardware.

Large ionospheric gradients acting between a Ground Based Augmentation System (GBAS) reference station and an aircraft on approach could lead to hazardous position errors if undetected. Current GBAS stations provide solutions against this threat that rely on the use of “worst-case” conservative threat models, which could limit the availability of the system. This paper presents a methodology capable of detecting ionospheric gradients in real time and estimating the actual threat model parameters based on a network of dual-frequency and multi-constellation GNSS monitoring stations. First, we evaluate the performance of our algorithm with synthetic gradients that are simulated over the nominal measurements recorded by a reference network in Alaska. Afterwards, we also assess it with one real ionospheric gradient measured by the same network. Results with both simulated gradients and a real gradient show the potential to support GBAS by detecting and estimating these gradients instead of always using “worst-case” models., Open access funding enabled and organized by Projekt DEAL., Peer Reviewed, Postprint (published version)

This is a post-peer-review, pre-copyedit version of an article published in Journal of geodesy. The final authenticated version is available online at: http://dx.doi.org/10.1007/s00190-021-01483-y, Global ionosphere maps (GIM) computed from dual-frequency GNSS measurements have been widely used for monitoring ionosphere as well as providing ionospheric corrections in Space Geodesy since 1998. This work focuses on a comprehensive study of the influence of time resolution on GIM performance. One and a half solar cycle of the IGS GIM with higher time resolution and accuracy (the UPC-IonSAT Quarter-of-an-hour time resolution Rapid GIM, AKA uqrg) has been taken as baseline to downsample them to all possible sub-daily temporal resolutions. The performance of the resulting GIMs has been assessed by directly comparing with external vertical total electron content (VTEC) measurements from Jason altimeters over oceanic regions. In order to perform a complete assessment and analysis of involved GIMs, the influence of geographical position and solar and geomagnetic activities was also taken into account during more than one solar cycle. In addition, to have a clear view at the smaller time resolutions, a more accurate assessment, the dSTEC test based on external GNSS measurements not used in the GIM generation was also done during two solstice and two equinox days in 2015 over continental regions. The assessment shows that discrepancy among GIMs with different time resolutions becomes more apparent at low latitudes and also at high solar-geomagnetic activity. The results also suggest that the accuracy for GIMs with time resolution smaller or equal to 60 min is consistent during the period from 2002 to 2019 and is more accurate than other GIMs with lower temporal resolution. Accordingly, high time resolution (including 15, 30, 45 and 60 min) is recommended for the application of GIMs with the highest accuracy., Peer Reviewed, Postprint (author's final draft)

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)

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)

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)

Weather forecast using GNSS-R relies, to a large extent, on data acquired by airborne and spaceborne platforms due to the extended coverage that can be achieved. GEO satellites can retrieve measurements over large areas but with spatial resolutions on the order of thousands of meters per pixel. LEO satellites with polar orbits can provide measurements over the entire world, but they cannot provide good spatial or high temporal resolutions by themselves. LEO constellations of small satellites have the same coverage with improved spatial resolution and revisit times by using data fusion techniques. High-altitude pseudo-satellites offer an excellent temporal and spatial resolution but only over limited areas. In this article, the potential of using hosted GNSS-R payloads on commercial aircraft is explored as an alternative and cost-effective means to achieve a very high resolution and a very low revisit time for regional environmental applications. Finally, a case study of soil moisture monitoring over Europe is presented, including an analysis of the expected performance., This work was supported in part by the projects of Spanish Ministerio de Ciencia, Innovación y Universidades and EU ERDF project un- der Grant RTI2018-099008-B-C21/AEI/10.13039/501100011033 “SENSING WITH PIONEERING OPPORTUNISTIC TECHNIQUES,” in part by the Grant MDM-2016-0600 to “Maria de Maeztu Excellence Research Units” CommSensLab, from Spanish Ministerio de Economía y Competitividad (MINECO/FEDER), and in part by the Recruitment of Early-Stage Research Staff under Grant FI-SDUR 2020 - 00105 of the Agència de Gestió d’Ajuts Universitaris i de Recerca (AGAUR)., Peer Reviewed, Postprint (published version)

Esta tesis presenta el diseño e implementación de la Visual Configuration Tool, y una sección de testing que describe la validación y el proceso de verificación deeste módulo de extensión del DSS-Sim.

There is an international consensus about considering internet access as a need, as a right that humanity needs to ensure to achieve a homogeneous development around the world, without differences. However, even in the most developed countries, the inequality in internet access is clear: the most habited and developed places enjoy fast, stable and reliable internet connections, while the less populated and less developed areas lack it. The projects of Low Earth Orbit satellite constellations are back to be considered as an alternative to connect the world, after years being considered non-viable because of the failure of the similar projects undertaken a couple of decades before. Nowadays, technological progress allows to afford the economic costs of the implementation, even scaling its size, ranging from the 66 satellites of Iridium¿s constellation to the hundreds, thousands, or tens of thousands of satellites for just one megaconstellation. In this work, we make an analysis of two of the most popular projects of megaconstellations at their initial stage, StarLink and OneWeb, in order to assess their performance, their coverage, and the suitability of their topology design. This study is made with the StarPerf software, developed by Tsinghua¿s University scientists. Lastly, the controversies around megaconstellations projects are reviewed, assessing the practical suitability of such technology and the potential threats they can arise in the area of astrophysics., Objectius de Desenvolupament Sostenible::10 - Reducció de les Desigualtats

Vessel traffic services (VTS) operators can control the movements of ships in localcoastal areas, and also have the technological ability to track vessels internationally,since all merchant vessels are currently equipped with global tracking systems. Digitalinformation processing and satellite communications are powerful tools that the mar-itime sector is eager to take advantage of in relation to safety, environmental protectionand efficiency. This paper reviews current regulations and infrastructures within theVTS and the main European Union (EU) projects that have utilized the potential of thedigital era and satellite technology. Through assessment of future trends, it alsoproposes, for the first time, that there will be the need for a new approach to globalmaritime traffic services, in view of anticipated issues in future developments withinthis sector. This approach will consider the creation of an oceanic vessel traffic services,where all personnel would exchange information, without state borders, between shipsand onshore centres worldwide. This also raises the issues of how a new technologicalparadigm will fare against ancient barriers of legislative scope., Postprint (author's final draft)

Context: The expansion of space applications and their liberalization is an actual fact since the last decade. Small satellites are developed either by academic institutions and private companies. The concept of femtosatelites, featuring a mass lower than a hundred grams, emerges from the need of deploying extensive constellations in order to get results as accurate as possible at the same time, while keeping low budgets, affordable to small research teams. Our femtosatellite,AtmoSwarm, is aimed to measure the thermospheric density as a function of the altitude and thickness of the layer. This layer of the atmosphere is nowadays barely studied, however, it is important, for instance, regarding the Sun-Earth relation or the re-entry trajectory of celestial bodies into the Earth. Aims: Positioning is vital for the success of our mission and the validation of the data obtained. This work is aimed at finding the most suitable Global Navigation Space System (GNSS) receiver in the market, following different operational requirements and specifications. Methodology: We apply a mathematical method based on a matrix decision, which allows us to shortlist the four models which better meet our mission requirements. In doing so, we have firstly carried out an extensive legal study of export regulations and operational limitations, such as COCOM, in order to be prepared to thoroughly explore actual GNSS receiver options in the existing market. During the selection process we have contacted the companies responsible for the GNSS receivers manufacture and distribution, obtaining feedback from both engineers and sales representatives. The information obtained was applied to develop a decision matrix and to obtain the corresponding Figures of Merit. Ultimately, this work was done in order to quantify and objectify the decision process, being able to adjust this method to a wide range of situations and requirements. Results: The method used proved efficient in optimizing the decision, Contexto: La liberalizacion de la industria espacial y sus aplicaciones se ha convertido én un hecho real durante la ultima d ´ ecada. Compa ´ n˜ías e instituciones se han puesto manos a la obra con el desarrollo de constelaciones de satelites con fines acad ´ emicos y ´ comerciales. El concepto de femtosatellite, destacando su masa inferior a cien gramos, emerge de la necesidad de constituir constelaciones con un gran numero de sat ´ elites ´ –con el objetivo de mejorar la precision de la informaci ´ on obtenida por estos– al mismo ´ tiempo que se mantiene un presupuesto asequible, al alcance de equipos de investigacion´ convencionales. Nuestro femtosatelite, llamado ´ AtmoSwarm, nace con el objetivo de medir la densidad de la termosfera en funcion de la altitud y el grueso de dicha capa. ´ Objetivos: El posicionamiento de nuestros satelites es vital para el buen desarrollo de la ´ mision as ´ í como para la correcta validacion de la informaci ´ on obtenida. El objetivo de este ´ proyecto se basa en encontrar el receptor GNSS que mejor se ajuste a nuestra mision, ´ teniendo en cuenta las necesidades de la misma. Metodología: En esta tesis haremos uso de metodos matem ´ aticos basados en matrices de ´ decision, lo que nos permitir ´ a listar aquellos modelos que cumplan mejor con nuestros re- ´ querimientos. Para ello, primero hemos llevado a cabo un estudio legal sobre regulaciones de exportacion, en concreto las del tipo COCOM (Coordinating Committee for Multilate- ´ ral Export Controls, por sus siglas en ingles), con el objeto de poseer el conocimiento ´ suficiente para explorar diferentes opciones de receptores GNSS disponibles en el mercado. Durante el proceso de seleccion hemos contactado con las empresas encargadas ´ de la fabricacion y distribuci ´ on de dichos aparatos, donde hemos tenido la oportunidad de ´ mantener reuniones tanto con ingenieros como representantes de ventas. La informacionóbtenida en estos encuentros se ha volcado en las matrices, para a

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)

In February 2019 a Project Authorization Request was approved by the Institute of Electrical and Electronics Engineers (IEEE) Standards Association with the title “Standard for Global Navigation Satellite System Reflectometry (GNSS-R) Data and Metadata Content”. A Working Group has been assembled to draft this standard with the purpose of unifying and documenting GNSS-R measurements, calibration procedures, and product level definitions. The Working Group (http://www.grss-ieee.org/community/technical-committees/standards-or-earth-observations/) includes members, collaborators, and contributors from academia, international space agencies, and private industry. In a recent face-to-face meeting held during the ARSI+KEO 2019 Conference, the need was recognized to develop a standard with a wide range of operations, providing procedure guidelines independently of constraints imposed by current limitations on geophysical parameters retrieval algorithms. As such, this effort aims to establish the fundamentals of a potential virtual network of satellites providing inter-comparable data to the scientific community., Peer Reviewed, Postprint (author's final draft)

Los sistemas de radionavegación por satélite (GNSSs) se han convertido en una herramienta indispensable de la vida diaria, ya que nos ofrecen la posibilidad de conocer de manera precisa nuestra ubicación en tiempo real y en entornos al aire libre. Desde la aparición de estos sistemas, han surgido una gran cantidad de exitosas aplicaciones de GNSS. Algunos ejemplos de estas aplicaciones son los siguientes: navegación para automóviles, rastreo de vuelos, seguimiento de actividad deportiva y juegos de realidad aumentada. Debido al éxito alcanzado por los sistemas de GNSS, un gran interés está surgiendo para extender sus servicios a entornos más complicados tales como cañones urbanos e interiores. No obstante, en estos entornos los receptores de GNSS tienen grandes dificultades para poder detectar las señales recibidas desde los satélites, las cuales son muy débiles ya que sufren una severa atenuación a causa de la presencia de obstáculos en el camino de propagación entre los satélites y el receptor. Esta tesis aborda varios problemas del procesamiento de señales de GNSS débiles como la detección en la etapa de adquisición, la determinación de la calidad de la señal y las estimaciones de la frecuencia Doppler y el tiempo de retraso. Para ello, se emplean las herramientas de detección y estimación de la señal, que se basan en teoría de probabilidad y estadística. Para poder emplear estas herramientas es necesario tener un conocimiento sobre la arquitectura y las señales que transmiten los sistemas de GNSS. Por este motivo, la primera parte de la tesis se centra en describir las principales características de dos de los sistemas de GNSS más conocidos el americano GPS y el europeo Galileo. Además, tratamos los fundamentos de los receptores y analizamos las señales que están implementadas actualmente en estos sistemas. Después, se explican los fundamentos de teoría de detección requeridos, que son el Neyman-pearson criterion, el Generalized likelihood Ratio Test y el Bayesi, Global Navigation Satellite Systems (GNSSs) have become an indispensable tool of daily life, since they offer us the possibility of accurately knowing our location in real time and in open-sky environments. Since the advent of these systems, a large number of successful GNSS applications have emerged. Some examples of these applications are: car navigation, flight tracking, sport activity tracking and augmented reality games. Due to the success achieved by GNSS, a great interest is emerging to extend its services to harsher environments such as urban canyons and indoor scenarios. However, in these environments GNSS receivers face great difficulties to detect the signals received from the satellites, which are very weak since they suffer from severe attenuation due to the presence of obstacles in the propagation path between satellites and the receiver. This thesis addresses several problems of processing weak GNSS signals, such as the detection at the acquisition stage, the determination of their signal quality and the time delay and Doppler frequency estimations. To do so, detection and estimation tools are used, which are based on the probability theory and statistics. In order to use these tools, it is necessary to understand the architecture and the signals that GNSSs transmit. For this reason, the first part of the thesis focuses on describing the main features of two of the best-known GNSSs, the American GPS and the European Galileo. In addition, we describe the fundamentals of the receivers and analyze the signals that are implemented in these systems. After that, we explain the required fundamentals of detection theory, namely the Neyman-pearson criterion, the Generalized Likelihood Ratio Test and the Bayesian approach. Then, a review of the state of the art in the detection of GNSS signals is carried out. The main contribution of this thesis is provided in the second part, which tackles the problem of deriving optimal detectors to acquire weak GNSS signals.

Global Navigation Satellite Systems (GNSSs) have improved the efficiency and accuracy of transportation means. In terms of safety, the European Geostationary Navigation Overlay System (EGNOS) is providing vertical and lateral guidance to civil aviation since 2011. Furthermore, EGNOS can support applications in other sectors such as maritime, railways and road.The present contribution aims to assess the use of EGNOS for maritime navigation compliant with the International Maritime Organization (IMO) requirements established in its Resolution A.1046 (27) for harbour entrances, harbour 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 authors would like to thank the Armed Institute of the Spanish Civil Guard for their assistance with the installation of equipment on-board their vessels that allowed collection of GNSS data, as well as for the navigation days across the Canary waters. The authors acknowledge the use of products provided by the International GNSS Service. EGNOS messages have been downloaded from SERENAD Data Server that belong to National Centre for Space Studies (CNES). The research reported in this paper was financially supported by the European GNSS Agency under contract GSA/OP/12/16/Lot1/SC1, Postprint (published version)

This TFM is involved in the ³Cat-4 project from the Nano-Satellite and Payload Laboratory. This project is also involved in the Fly Your Satellite! II program of the ESA Academy and will be directed with the colaboration of Joan Adrià Ruiz de Azua Ortega.

Currently, the forecast for the European market for IoT is a yearly 19.8% increase up to reach $241 billion in 2025. Thisstrong growing will be concentrated in verticals from manufacturing, utilities, retail and transportation [1], [2]. However, in orderto monetize the potential services over IoT it is necessary to guarantee the security of the communications [3]. In this regardphysical-layer security methods may complement higher-layer encryption techniques by exploiting the characteristics of wirelesschannels. For this purpose, it is resorted to the secrecy-capacity metric to measure the security level. More specifically, it was shownin [4] that reliable information-theoretic security could be achieved, whenever the eavesdropper’s channel be a degraded versionof the legitimate user’s channel. In this case, if the secrecy rate is chosen below the secrecy-capacity, then reliable transmissionscan be achieved in perfect secrecy. However, the time-varying fading effect of wireless channels degrades the secrecy-capacity. Inthis situation, it is used the ergodic capacity to measure the secrecy-capacity [5]. In order to make the overhearing process of theeavesdroppers difficult, it is used the time-packing/faster than Nyquist strategy [6]- [7].Thus, the time-duration of the transmittedframes are reduced which: i) improves the interception probability of the packets, ii) augments the spectral efficiency of theM2M communications without increasing the transmission bandwidth, iii) diminishes the effect of Doppler spread in Non-GEOcommunications, and iv) permits to use the overlapping degree among the pulse shapes to boost the secrecy-capacity. On thecontrary, this overlapping degree introduces a multi-path channel that may difficult the synchronization process. However, thecoefficients of the multipath channel are known by the legitimate user but ignored by the eavesdropper. This strategy of securityis similar to that the Artificial Noise (AN) one pursues [5], [8]- [9], but, Peer Reviewed, Postprint (published version)

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works, In a multi-beam satellite communication system, traffic requests are typically asymmetric across beams and highly heterogeneous among terminals. In practical operations, it is important to achieve a good match between the offered and requested traffic, i.e., to improve the performance of Offered Capacity to requested Traffic Ratio (OCTR). Due to satellites' payload constraints and limited flexibilities, it is a challenging task for resource optimization. In this paper, we tackle this issue by formulating a max-min resource allocation problem, taking fairness into account such that the lowest OCTR can be maximized. To exploit the potential synergies, we introduce Non-Orthogonal Multiple Access (NOMA) to enable aggressive frequency reuse and mitigate intra-beam interference. Although NOMA has proven its capabilities in improving throughput and fairness in 5G terrestrial networks, for multi-beam satellite systems it is unclear if NOMA can help to enhance the OCTR performance, and hence is worth quantifying how much gain it can bring. To solve the problem, we design a suboptimal algorithm to firstly decompose the original problem into multiple convex subproblems by fixing power allocation for each beam, and secondly adjust beam power to improve the minimum OCTR in iterations. Numerical results show the convergence of the proposed algorithm and the superiority of the proposed NOMA scheme in max-min OCTR., Peer Reviewed, Postprint (author's final draft)

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., Non-orthogonal transmission is a promising technology enabler to meet the requirements of 5G communication systems. Seminal papers demonstrated that non-orthogonal multiplexing techniques outperform orthogonal schemes in terms of capacity, latency, and user fairness. Since it is envisioned that satellites will be an integral component of the 5G infrastructure, it is worth studying how satellite communication systems can benefit from the application of non-orthogonal transmission schemes as well. Contrary to common perception, current communications through a satellite present a different architecture and face different impairments than those in the wireless terrestrial links. In particular, this work aims to describe different non-orthogonal schemes that are suitable for the forward link (i.e., satellite to user). In contrast with the return link of the satellite (i.e., user to satellite), where the use of non-orthogonal transmission schemes has been widely studied, less effort has been devoted to the forward link. In light of this, this article provides an overview and a novel taxonomy that is based on the forward link of different non-orthogonal multibeam transmission schemes. Finally, guidelines that open new avenues for research in this topic are provided., Peer Reviewed, Postprint (author's final draft)

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., The field of satellite communications (SatCom) is enjoying renewed attention in the global telecommunications market, and high-throughput satellites, with their multiple spot beams, are critical components for delivering the rates that will be demanded in the future. In this article, we present the state of the art and the open research challenges in the area of high-throughput satellites, with a focus on signal processing approaches for efficient interference mitigation., Peer Reviewed, Postprint (author's final draft)

During these years, novel Distributed Satellite Systems (DSS) have addressed the new Earth Observation (EO) requirements (e.g. near-real time access to data, or multi-point observations). One of the DSS proposals is the concept of Federated Satellite System (FSS) which has explored the benefits of sharing available and unused resources between satellite to maximize the system utility. The possibility to use additional downlink opportunities thanks to federations is a resource that could improve current EO missions, and thus achieving the required performance. For that reason, the FSS Experiment payload has been implemented as a FSS proof-of-concept between 6-Unit CubeSats in the FSSCAT mission. This article presents the design, and the test results of this payload demonstrating its feasibility for future EO missions., Peer Reviewed, Postprint (published version)

This is the peer reviewed version of the following article: Mendoza, F, Ferrus, R, Sallent, O. Experimental proof of concept of an SDN‐based traffic engineering solution for hybrid satellite‐terrestrial mobile backhauling. Int J Satell Commun Network. 2019; 37: 630– 645, which has been published in final form at https://doi.org/10.1002/sat.1303. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving, Satellite networks are expected to be an integral part of 5G service deployment. One compelling use case is mobile backhauling, where the exploitation of a satellite component can improve the reach, robustness, and economics of 5G rollout. The envisaged availability of new satellite capacity, together with the development of better integration approaches for the provisioning and operation of the satellite component in a more flexible, agile, and cost-effective manner than done today, are expected to revamp such use case within the 5G ecosystem. In this context, sustained in the architectural designs proposed within H2020 VITAL research project, this paper presents an experimental proof of concept (PoC) of a satellite-terrestrial integration solution that builds upon software-defined networking (SDN) technologies for the realization of end-to-end traffic engineering (E2E TE) in mobile backhauling networks with a satellite component. A laboratory test bed has been developed and validated, consisting of a small-scale private mobile network with a backhaul setting that combines Ethernet-wired links, a satellite link emulator (OpenSAND), OpenFlow switches, and an OpenFlow controller running the network application for E2E TE. Provided results show the operation of a E2E TE application able to enforce different traffic routing and path failure restoration policies as well as the performance impact that it has on the mobile network connectivity services., Peer Reviewed, Postprint (author's final draft)

Interference Management is a vast topic present in many disciplines. The majority of wireless standards suffer the drawback of interference intrusion and the network efficiency drop due to that. Traditionally, interference management has been addressed by proposing signal processing techniques that minimize their effects locally. However, the fast evolution of future communications makes difficult to adapt to new era. In this paper we propose the use of Deep Learning techniques to present a compact system for interference management. In particular, we describe two subsystems capable to detect the presence of interference, even in high Signal to Interference Ratio (SIR), and interference classification in several radio standards. Finally, we present results based on real signals captured from terrestrial and satellite networks and the conclusions unveil the courageous future of AI and wireless communications., Peer Reviewed, Postprint (published version)

The Unmanned Aircraft Vehicles (UAV) industry has grown at such an amazing rate, that it is almost impossible to count or describe all the applications that have become normal practice, not to mention the number of companies involved in either making drone platforms or supplying drone integrators with sensors: GNSS receivers, inertial sensors, LiDAR, photographic, thermal and infrared cameras, video and more. In particular, positioning systems have become crucial for almost all industrial drone’s applications, such as photogrammetry, 3D mapping, search and rescue operations, surveillance… Beyond the use of computed positions of the drone for professional matters, the need to “getting the right position to fly safely” is of the utmost importance. Yet, most of the GNSS receivers on-board of drones provide low-quality data, with no expected changes in the long-term, principally because of their cost and weight. Then, new questions are arising: Is the low-quality position data good enough for current or new applications? Are there other technologies, systems or methods able to improve performance without changing the drone’s GNSS receivers? The answer is positive: SBAS augmentation system is a complement to GPS built initially for civil aviation, but available to GNSS receivers, even those from drones. It is a method reduce more than a half the position error (accuracy) and also gives additional information in order to quantify how bad the measurements are (integrity). This document will explain how a software able to calculate GPS-based positioning augmented with SBAS has been developed and then, the results of it are assessed in order to analyse if the system would be useful in drone applications or operations

Las fulguraciones estelares son incrementos repentinos de radiaciones electromagnéticas en la superficie de una estrella que contienen gran cantidad de energía. Son detectadas por telescopios tales como Swift o Fermi realizando observaciones desde satélites artificiales en órbita baja terrestre. Esta radiación también afecta al contenido total de electrones de la ionosfera terrestre. Esto permite una alternativa para detectar las fulguraciones: detectar el incremento repentino y según un cierto patrón espacial característico del mencionado contenido de electrones, que puede ser procesado usando las medidas transionosféricas en doble frecuencia de los Sistemas de Navegación Global por Satélite (Global Navigation Satellite Systems, GNSS), como por ejemplo GPS. Se propone el algoritmo Blind GNSS Search of Extraterrestrial EUV Sources (BGSEES) para detectar fulguraciones solares sin conocimiento previo de la posición de la fuente, es decir, la posición del Sol relativa a la de la Tierra en la caracterización del algoritmo ante fulguraciones solares conocidas, así como un estudio sobre la viabilidad de la detección de fulguraciones que tienen lugar en estrellas lejanas. El objetivo final es el de confirmar la validez de un nuevo método de detección alternativo al de los telescopios que use datos de libre acceso y sea omnidireccional., Stellar flares are sudden electromagnetic emissions on a star's surface that release large amounts of energy. These flares are detected by telescopes such as Swift or Fermi by performing radiation observations from low Earth orbit. However, the radiation also has an effect on Earth's ionosphere electron content. Another approach for detecting these events is possible: the aforementioned electron content variation can be processed using data from Global Navigation Satellite Systems (GNSS) such as GPS to study the flares. The Blind GNSS Search of Extraterrestrial EUV Sources (BGSEES) algorithm for detecting solar flares without knowing the location of the source, that is, the position of the Sun relative to Earth, is presented, as well as a study on the feasibility of the detection of such events for the challenging scenario of far-away stars, aiming to find an alternative detection method to that of the telescopes and using free, open access data.