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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 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)

Significant Wave Height (SWH) is a key parameter to characterize waves, which is typically used in sea state monitoring such as wave forecast to ensure ocean navigation safety. Satellite radar altimeter is probably the primary tool to obtain SWH information. However, it cannot be used for large-scale sea state monitoring unless many of theses satellites are deployed. In this article, we aim to study the potential of Global Navigation Satellite System (GNSS)-Reflectometry (GNSS-R) in SWH measurement based on spaceborne Delay-Doppler Maps (DDMs) data. First, 3 observables (i.e., Delay-Doppler Map Average (DDMA), leading edge slope (LES) of normalized integrated delay waveform (NIDW) (LES-NIDW), and trailing edge slope (TES) of NIDW (TES-NIDW) derived from the DDMs are introduced for SWH estimation. Then, an empirical SWH retrieval model is proposed based on three observables. Subsequently, ERA5 SWH is used as reference data to verify the performance of the proposed model. The experimental results show that the Root Mean Square Error (RMSE) and Correlation Coefficient (CC) estimated by SWH of the three observables are better than 0.54 m and 0.88 m, respectively. Among them, the estimation performance based on DDMA observable is the best, with RMSE and CC of 0.49 m and 0.89 m. This study shows the potential of spaceborne GNSS-R in SWH retrieval. © 2022 IEEE., This work was supported by the Grant RYC-2016-20918 financed by MCIN/AEI /10.13039 /501100011033 and by ESF Investing in your future., Peer Reviewed, Postprint (published version)

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)

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

In conjunction to the extensive research conducted in outdoor positioning and navigation systems, indoor localization and navigation techniques have been gaining interest and attention with various technologies proposed in an attempt to achieve high positioning accuracy. Out of many proposed techniques, the received signal strength (RSS) fingerprinting-based approach remains widely adopted for indoor localization. One of the key challenges facing this approach is navigating an open space indoor location where the signal strength may vary indifferently from one position to the subsequent one. In this work, we propose a transduction neural network approach that takes as an input a sequence of past RSS fingerprints and accordingly predicts the current location, navigates the movement, and even predicts the future positions. The proposed models are based on Gated-Recurrent Unit (GRU) and Long-Short Term Memory (LSTM) recurrent neural networks (RNN). Moreover, we compare the accuracy of the proposed transduction neural networks to a non-recurrent neural network, then we evaluate the performance of all suggested models in a realistic environment with only WLAN RSS fingerprints, Cellular RSS Fingerprints, and both WLAN/Cellular RSS fingerprints. Our experimental results show that the LSTM-based architecture achieves accuracy of about one meter in an open area of 130m2 while only using Wi-Fi fingerprints.

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)

© 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., Thanks to the successful operations of the UK TDS-1 and NASA CYGNSS GNSS-R missions, a wealth of Delay-Doppler Maps (DDM) are being measured from the ocean, but also from land reflections. Using the land reflected DDM, several studies are being conducted to retrieve the land geophysical parameters, such as soil moisture, vegetation depth, and biomass. Although they have shown the dependence of the land geophysical parameters on the DDM, it is also shown that many other parameters impact the DDM. This work presents the impacts of some parameters on the DDM. For the systematical and efficient study, an E2E simulator is used. The simulator generates the synthesized DDM reflected over land varying the input parameters, which are the specular point position on the Earth, the elevation angle at the specular points, soil moisture, etc. From the simulation results, the relation between the input parameters and the DDM is individually analyzed, providing the clue to the retrieval algorithm of the geophysical parameters., Peer Reviewed, Postprint (author's final draft)

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)

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.

Ionospheric anomalies, like large ionospheric gradients, might produce a difference between the ionospheric error experienced bythe Ground Based Augmentation System (GBAS) reference station and the aircraft on approach. This ionospheric delay differencecould lead to hazardous position errors if undetected.For that reason, the GBAS Approach Service Types (GAST) C and D provide solutions against this threat, but the methodsemployed still face challenges by limiting the availability in certain cases, especially in regions with severe ionospheric conditions.This issue is caused by the use of very conservative ionospheric threat models derived based on the worst-ever-experiencedionospheric gradients in the relevant region. However, these worst-case gradients occur very rarely.Therefore, this paper proposes a methodology capable of detecting ionospheric gradients in real-time and estimating theirparameters in near real-time by using a wide area network of dual-frequency and multi-constellation GNSS monitoring stations.Hence, the GBAS stations could use this information to update the threat model currently applied in their algorithms, which wouldresult in an improvement of the GBAS availability in regions where it is degraded.The detection and estimation algorithm is initially theoretically explained. Then, the performance of this algorithm is evaluatedwith simulated gradients and with a real gradient, utilizing for both the real measurements recorded by a reference networkin Alaska. The synthetic gradients are simulated over the nominal real measurements from this network and all the gradientparameters are modified within their ranges in the already existing threat models. In this way, we assess the performance of ouralgorithm by comparing the differences between the known simulated gradient parameters and the parameters estimated by ouralgorithm. Additionally, we also evaluate our algorithm with one real ionospheric gradient measured by the same network inAlaska to study, Peer Reviewed, Postprint (author's final draft)

Global Navigation Satellite System Reflectometry and L-band microwave radiometry have been used for soil moisture, biomass, and cryosphere studies. Combining both technologies in a low-power and cost-effective solution could largely improve current Earth observations. 3 Cat-4 mission is a 1-Unit CubeSat technology demonstrator of the Flexible Microwave Payload - 1, a reduced size payload that combines these two technologies. This work presents the objectives of the 3 Cat-4 mission and the details of the spacecraft architecture and performance. Each spacecraft subsystem is detailed at hardware and software levels. In addition, the presented results indicate that the current spacecraft design will survive the flight conditions (i.e. thermal and structural ones)., 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., The security in satellite communications is a key issue due to the large footprint of the beams. This is specially critical in IoT devices that transmit data directly to satellite. Take into account that IoT devices are characterized by transmitting packets of short length. Consequently, it means that it is not feasible to augment the security level of the IoT packets via complex cryptographic algorithms. Otherwise, their packet lengths may be increased in a non-negligible way which could augment their collision probabilities, latencies and energy consumptions. For this reason, this paper proposes to take advantage of the time-packing technique. By doing so, it is possible to use the overlapping degree among the pulse-shapes to boost the secrecy-capacity. In particular, the overlapping degree between the pulse-shapes introduces an artificial interference that degrades the eavesdropper's channel. In this regard, it is necessary to highlight that there is a residual co-channel interference in the satellite beams. So, it means that these two sources of impairments make difficult to estimate the legitimate user's transmission parameters by the eavesdropper., Peer Reviewed, Postprint (author's final draft)

Satellite Precoding is a promising technique to meet the target data rates of the future high throughput satellite systems and the costs per bit as required by 5G applications and networks, but it requires strict synchronization among the transmitted waveforms, in addition to accurate channel state information. Most of the published work about this topic consider ideal oscillators, but in practice, the output of an oscillator is not a single spectral line at the nominal frequency. This paper proposes a model for the oscillator phase noise and analyzes the resulting received signal to interference plus noise ratio (SNIR) in a satellite communication system using Precoding. Simulations of a communication satellite system with a two-beam transponder and two receivers were performed to compute the effective SNIR. This work uses a simulator which also considers practical impairments such as time misalignment, errors in the channel state information, interference, thermal noise and phase noise masks for satellite oscillators. The Precoding methods used for the analysis are Zero Forcing (ZF) and Minimum Mean Square Error (MMSE). The obtained results prove that there is a degradation in the performance due to the use of independent oscillators but this effect is compensated by the precoding matrix., Peer Reviewed, Postprint (author's final draft)

A demonstration study to examine the feasibility of retrieving dust radiative effects based on combined satellite data from MODIS (Moderate Resolution Imaging Spectroradiometer), CERES (Clouds and the Earth's Radiant Energy System) and CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) lidar vertical profiles along their orbit is presented. The GAME (Global Atmospheric Model) radiative transfer model is used to estimate the shortwave and longwave dust radiative effects below the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite) orbit assuming an aerosol parameterization based on the CALIOP vertical distribution at a horizontal resolution of 5¿km and additional AERONET (Aerosol Robotic Network) data. Two study cases are analyzed: a strong long-range transport mineral dust event (aerosol optical depth, AOD, of 0.52) that originated in the Sahara Desert and reached the United Kingdom and a weaker event (AOD¿=¿0.16) that affected eastern Europe. The radiative fluxes obtained are first validated in terms of radiative efficiency at a single point with space–time colocated lidar ground-based measurements from EARLINET (European Aerosol Research Lidar Network) stations below the orbit. The methodology is then applied to the full orbit. The strong dependence of the radiative effects on the aerosol load (and to a lesser extent on the surface albedo) highlights the need for accurate AOD measurements for radiative studies. The calculated dust radiative effects and heating rates below the orbits are in good agreement with previous studies of mineral dust, with the radiative efficiency obtained at the surface ranging between -80.3 and -63.0¿W¿m-2 for lower dust concentration event and -119.1 and -79.3¿W¿m-2 for the strong event. Thus, results demonstrate the validity of the method presented here to retrieve 2-D accurate radiative properties with large spatial and temporal coverage., Peer Reviewed, Postprint (published version)

The design of autonomous operational schemes for distributed, decentralized systems is expected to bring multiple qualities to systems of this kind. One of their instances are Earth-observing swarms of nano-satellites, in which their collective function targets global performance figures. The design of autonomous operations can be modelled as a collective scheduling problem subject to resource constraints. There are many system-wide qualities of interest, such as resiliency, adaptability, responsiveness, among others, that need specific frameworks to characterize the proposed solutions. This paper presents one such design-oriented tool that can evaluate these autonomous organization schemes-potentially for large-scale and highly heterogeneous scenarios with dynamic contexts and multiple time-scales-and illustrates its usage in the evaluation of an autonomous nano-satellite swarm that collectively optimizes revisit times., Peer Reviewed, Postprint (published version)

This paper discusses about GNSS-based positioning and timing in challenging propagation conditions for receivers featuring an array of antennas with an arbitrary distribution. In particular, the positioning and timing problems are treated as multiple-input multiple-output (MIMO) estimation problems in which all the GNSS signals received by the array of antennas are jointly exploited in the corresponding domain. The MIMO-GNSS processing approach is targeting the derivation of robust solutions in the presence of realistic signal impairments introduced by the propagation channel or any other external interference. The maximum likelihood estimator (MLE) in the MIMO-GNSS framework is reviewed, and simulation results in realistic challenging scenarios are presented, showing the benefits introduced by the exploitation of arrays of antennas in both positioning and timing., Peer Reviewed, Postprint (published version)

The main objective of this work is contributing into the development of one satellite missions’ simulator. Specifically, the main part to work in is the scheduler, the task manager that decides how the simulator must behave during the full mission. Other software improvements will be done too. The scheduler is the internal logic that the on-board computer/s of a satellite must follow in order to satisfy the mission objectives. It takes into account the requirements and constrains of the power, thermal and data budgets. Depending on the state of the budgets it evaluates if the different satellite subsystems must be: active, inactive or must change the way that they are operating. So it can take action using commands if is needed because it works in a fully-independent-way. This work will improve the current scheduler of a satellite simulator, making him more efficient, resistant and customizable. Different working modes will be implemented in the simulator in order to avoid the collapse of the budgets. The mode changes logic and the capabilities of each one of the working modes will be the key of improving the scheduler. Previous to the code implementation, a theoretical research will be done in order to understand the different components that play a roll into the different budgets. The other software improvements are functionalities added to the simulator to make him more realistic and useful for a huger range of space mission. A precision “submode” is implemented for example. Also some satellite parameters are studied in order to see its affectation to the three budgets. Examples could be the chassis paint affectation or the overvoltage of the subsystems. During the report, lots of plots and maps obtained from the simulator will be showed to the reader to see how the different improvements affect. Finally, a 90 days mission simulation will be done in order to comment the obtained results., L‟objectiu principal d‟aquest treball és contribuir al desenvolupament d‟un simulador de missions per satèl·lit. En concret, la part principal a treballar és el planificador, el gestor de tasques que decideix com ha de comportar-se el simulador durant la missió completa. També es faran altres millores en el programari. El planificador és la lògica interna que han de seguir els ordinadors de bord d'un satèl·lit per satisfer els objectius de la missió. Té en compte els requisits i limitacions dels pressupostos d'energia, de calor i de dades. Depenent de l'estat dels pressupostos, avalua si els diferents subsistemes de satèl·lit han de ser: actius, inactius o han de canviar la manera en què funcionen. Per tant, pot actuar fent servir ordres si cal, perquè funciona de manera totalment independent. Aquest treball millorarà el planificador actual d'un simulador de satèl·lits, fent-lo més eficient, resistent i personalitzable. S‟implementaran diferents modes de funcionament al simulador per evitar el col·lapse dels pressupostos. La lògica dels canvis de mode i les capacitats de cadascun dels modes de treball seran la clau per millorar el planificador. Prèviament a la implementació del codi, es farà una investigació teòrica per entendre els diferents components que apareixen els diferents pressupostos. Les altres millores de programari són funcionalitats afegides al simulador per fer-lo més realista i útil per a una àmplia gamma de missions espacials. Per exemple, s‟implementa un "submode" de precisió. També s‟estudien alguns paràmetres de satèl·lit per veure la seva afectació als tres pressupostos. Alguns exemples podrien ser l‟afectació de la pintura de xassís o la sobretensió dels subsistemes. Durant l‟informe, es mostraran al lector moltes gràfiques i mapes obtinguts del simulador per veure com afecten les diferents millores. Finalment, es farà una simulació de missió de 90 dies per comentar els resultats obtinguts.

© 2018 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., This work addresses the optimization of the network spectral efficiency (SE) under successive interference cancellation (SIC) at a given blocklength n. We adopt a proof-of-concept satellite scenario where network users can vary their transmission power and select their transmission rate from a set of encoders, for which decoding is characterized by a known packet error rate (PER) function. In the large-system limit, we apply variational calculus (VC) to obtain the user-energy distribution, the assigned per-user rate and the SIC decoding order maximizing the network SE under a sum-power constraint at the SIC input. We analyze two encoder sets: (i) an infinite set of encoders achieving information-theoretic finite blocklength PER results over a continuum of code rates, where the large-n second order expansion of the maximal channel coding rate is used; (ii) a feasible finite set of encoders. Simulations quantify the performance gap between the two schemes., Peer Reviewed, Postprint (author's final draft)

The 3 Cat-3/MOTS mission is a joint initiative between the Institut Cartogràfic i Geològic de Catalunya (ICGC) and the Universitat Politècnica de Catalunya-BarcelonaTech (UPC) to foster new and innovative technologies on Earth Observation (EO) based on the data fusion of Global Navigation Satellite Systems Reflectometry (GNSS-R) and optical payloads on a 6U CubeSat platform. The final objective of the mission is to provide soil moisture mapping through the GNSS-R payload and improve its resolution by data fusion with the multi-spectral optical data acquired. This technique has been successfully applied to SMOS, but never performed from a 6U CubeSat carrying both payloads. An airborne optical and GNSS-R field experiment has been carried out to test/develop the algorithm and to analyze the results both separately (GNSS-R + optical data) and as a soil moisture product, once performed the data fusion., Peer Reviewed, Postprint (published version)

Aquest treball és un estudi sobre el sistema de Posicionament dinàmic o sistema DP (Dynamic Positioning), tenint com a objectiu un anàlisi total sobre aquest sistema de navegació i posicionament. Aquest sistema consisteix en un conjunt de sensors, monitors i un sistema de propulsió que, a temps real, és capaç de corregir els efectes del vent, la corrent i l’onatge per a mantenir una embarcació en una localització concreta i de forma estàtica. En les últimes dècades, el posicionament dinàmic ha estat un tema molt innovador i ha proporcionat un gran desenvolupament en el món marítim. Així doncs, la intenció i objectiu d\'aquest treball és obtenir com a fruit un coneixement avançat sobre aquest sistema, saber com va sorgir el terme de posicionament dinàmic, conèixer els seus components i parts, conèixer tant les seves limitacions com els seus avantatges, la seva classificació actual i els seus usos i aplicacions. A més, s’entendrà i es comprendrà el funcionament tant en el seu conjunt com en les seves diferents parts, sabent diferenciar cadascun dels tipus i la raó per la qual és tan important en el sector marítim tant en el passat, l’actualitat i el futur pròxim. Es farà incís en certs conceptes i aspectes del Posicionament Dinàmic per abastir un coneixement més ampli i acurat. Al llarg del Treball s’anirà analitzant i diferenciant termes en cadascun dels apartats, evitant confusions i possibles contrarietats per tot el que fa referència al sistema de posicionament dinàmic. Per últim, es veurà l’ampli ventall de tipologies de vaixell que s’utilitzen avui en dia amb el sistema DP i s’entendran les aplicacions i operacions que són capaços de realitzar. Amb elles, es veurà el paper tant important que desenvolupa en l\'actualitat.

This is a pure signal-processing project that is focused on minimize as much as possible the effects caused by the ionosphere over the carrier phases of signals emitted by GPS satellites. These effects are highly related with the solar activity over the GNSS/Galileo receiver signals emitted by a certain number of satellites. This is a real and concrete problem with high scientific and industrial interest. It is exposed and explained the recent advances on the ionospheric models and basic GNSS and Galileo receiver architectures. Then, two different algorithms (single channel and multi-channel), whose objective is to detect step-anomalies (known as cycle slips) in the carrier phases, are structured and explained in detail. Multi-channel algorithm performs other adaptive algorithms, whose is demonstrated with computer simulations under moderated and severe perturbed ionosphere, modifying for each simulation the parameters of some implemented navigation equations which are determined by the motion of the receiver and the satellites. After several simulations and compiling different results, both single and multi-channel algorithms have been compared and it has been proved the superiority of the multi-channel algorithm., Este proyecto se enfoca principalmente en minimizar lo máximo posible los efectos causados por la ionosfera sobre las fases portadoras de las señales emitidas por distintos satélites GPS. El origen de estos efectos de la ionosfera está relacionado con la alta actividad solar sobre las señales de los receptores GNSS/Galileo. Éste es un problema real y concreto que cuenta con un alto interés científico e industrial. Se exponen y explican los avances más recientes en los modelos ionosféricos y las arquitecturas básicas de los receptores GNSS y Galileo. Luego, se explican en detalle dos algoritmos propuestos para este trabajo, el algoritmo monocanal y el multicanal, cuyo objetivo es detectar en qué satélite y cuándo se han producido discontinuidades (conocidas como cycle slips) en las fases portadoras. El algoritmo multicanal también desarrolla adaptativos, y se demuestra su funcionalidad con simulaciones computarizadas bajo perturbaciones moderadas y severas de la ionosfera, modificando para cada simulación los parámetros de las ecuaciones de navegación implementadas y determinadas por el movimiento del receptor y los satélites. Finalmente después de varias simulaciones y de recopilación de datos, los algoritmos han sido comparados, dónde se demuestra la gran superioridad del algoritmo multicanal frente al monocanal., Aquest projecte s'enfoca principalment en minimitzar el màxim possible els efectes causats per la ionosfera sobre les fases portadores dels senyals emesos per diferents satèl·lits GPS. L?origen d?aquests efectes de la ionosfera està relacionat amb l'alta activitat solar sobre els senyals dels receptors GNSS/Galileo. Aquest és un problema real i concret amb alt interès científic i industrial. S?exposen i expliquen els avenços més recents en els models ionosfèrics i les arquitectures bàsiques dels receptors GNSS i Galileo. Després, s?estructuren en detall els dos algorismes proposats per aquest treball, l?algorisme monocanal i el multicanal, l?objectiu dels quals es detectar on quan s?han produït discontinuïtats (conegudes com cycle slips) a les fases portadores. L?algorisme multicanal també implementa algorismes d?adaptació i es demostra la seva funcionalitat amb simulacions computeritzades sota pertorbacions moderades i severes de la ionosfera, modificant per a cada simulació els paràmetres de les equacions de navegació implementades i determinades pel moviment del receptor i els satèl·lits. Finalment després de diverses simulacions i de recopilació de dades, els algoritmes han estat comparats, on es demostra la gran superioritat de l?algorisme multicanal davant de l?algorisme monocanal., Aquest projecte s'enfoca principalment en minimitzar el màxim possible els efectes causats per la ionosfera sobre les fases portadores dels senyals emesos per diferents satèl·lits GPS. L'origen d'aquests efectes de la ionosfera està relacionat amb l'alta activitat solar sobre els senyals dels receptors GNSS/Galileo. Aquest és un problema real i concret amb alt interès científic i industrial. S'exposen i expliquen els avenços més recents en els models ionosfèrics i les arquitectures bàsiques dels receptors GNSS i Galileo. Després, s'estructuren en detall els dos algorismes proposats per aquest treball, l'algorisme monocanal i el multicanal, l'objectiu dels quals es detectar on quan s'han produït discontinuïtats (conegudes com cycle slips) a les fases portadores. L'algorisme multicanal també implementa algorismes d'adaptació i es demostra la seva funcionalitat amb simulacions computeritzades sota pertorbacions moderades i severes de la ionosfera, modificant per a cada simulació els paràmetres de les equacions de navegació implementades i determinades pel moviment del receptor i els satèl·lits. Finalment després de diverses simulacions i de recopilació de dades, els algoritmes han estat comparats, on es demostra la gran superioritat de l'algorisme multicanal davant de l?algorisme monocanal.

Global Navigation Satellite Systems – Reflectometry (GNSS-R) is a relatively new remote sensing technique that benefits from GNSS signals as signals of opportunity as a bistatic radar. These signals can be processed as a scatterometer by measuring the relative scattered power, as an altimeter by measuring the relative delay between the direct and the scattered signals, and as an unfocused Synthetic Aperture Radar (SAR) with very short coherent integration times (typically a few millisecons). Wider bandwidth signals provide an opportunity to increase the performance of some GNSS reflectometry applications (i.e. altimetry). The Microwave Interferometric Reflectometer (MIR) is an instrument developed at UPC to compare different GNSS-R techniques, notably the conventional and interferometric ones, and assess the capabilities of these new signals and bands of the GPS and Galileo systems (L1/E1 and L5/E5). This paper describes the MIR beamforming system., Peer Reviewed, Postprint (published version)

The 3 Cat-4 mission aims to demonstrate the capabilities of nano-satellites plus the versatility of a Software Defined Radio for passive Earth Observation. Three different microwave payloads are integrated into a single unit CubeSat platform: a multi-constellation (GPS and Galileo) and a dual-band (L1 and L2) Global Navigation Satellite System - Reflectometer receiver, a total power radiometer including a novel Radio Frequency Interference (RFI) detection and mitigation technique, and an Automatic Identification System receiver for vessels tracking. Being able to validate these technologies in a CubeSat enables their fast adoption as hosted payloads or in more performing dedicated platforms in the future. This paper shows a novel approach for embedding multiple passive microwave payloads in a single platform., Peer Reviewed, Postprint (published version)

Satellite architectures where networked, heterogeneous observation nodes capture data in a distributed manner are seen as feasible solutions to address the needs of next-generation Earth observation services (i.e. higher spatial, spectral and temporal resolutions at viable costs). Nevertheless, the problems that designers face when approaching these systems-of-systems are still eclipsed by the heterogeneity, dimensionality and multi-level complexity of those. In spite of the many underlying technological challenges, how to optimally architect distributed satellite systems, remains an open source of debate. In this context, this paper presents a design-oriented methodology that is aimed at providing high-level design solutions for this type of architectures in generic EO use-cases. In order to find optimal solutions, the methodology detailed in this paper is grounded on an aggregated architectural figure-of-merit that compresses: (a) system-level performance metrics; (b) use-case requirements; (c) development and launch costs; and (d) a set of architectural quality attributes. The latter contributing term models, assesses and weights several of the so-called 'ilities' of an architecture and allows to select designs that exhibit some desired qualities. With a dimensionality of more than five thousand architectural alternatives, the study has been illustrated with a marine weather forecast use-case. Both the exploration of design alternatives and the analysis of the results have shown the benefits of medium and small satellite platforms and have stressed their potential in the design of distributed satellite systems. Finally, this paper concludes by suggesting that this very optimization framework and methodology could also be used for a quantitative gap analysis aiming at deriving the technological road map for future engineering teams., Peer Reviewed, Postprint (published version)

Global change is increasing the risk of forest decline worldwide, impacting carbon and water cycles. Hence, there is an urgent need for predicting forest decline occurrence. To that purpose, this study links forest decline events in Catalonia, detected by the DEBOSCAT forest monitoring program, with information from the Soil Moisture and Ocean Salinity (SMOS) satellite. Firstly, this study reviews the role of the SMOS soil moisture in a previous forest decline episode occurred in 2012, where the authors concluded that dry soils increased the probability of observing decline in broadleaved forests. Secondly, the present study detects that forest decline in 2012 and 2016 was linked to very dry soil conditions (generally with SM<;0.06 m 3 ·m -3 ). A similar analysis is proposed using SMOS Vegetation Optical Depth (VOD) data, which is a proxy of vegetation hydric status. Results and preliminary models will be presented at IGARSS 2018., Peer Reviewed, Postprint (published version)

The characterization of the ionosphere and its impact on the propagation of radio-wave signals has received an increasing interest for satellite communications, Global Navigation Satellite Systems (GNSS) applications (i.e. navigation and timing), and Earth Observation (EO) missions, especially low frequency SAR missions and GNSS-Reflectometry (GNSS-R). Although the main climatological models for the mean stable part of the electron density in the ionospheric layers (e.g. IRI or NeQuick) or for the magnetic field (e.g. WMM) have been significantly improved in the past years, the inhomogeneous part, responsible for scintillation effects, can still be significantly improved, since models are based on relatively old data (e.g. WBMOD), or the climatological inputs are limited to properly characterize all latitudes and solar conditions (e.g. GISM or WAM). ESA's CLIM IONO study aims to use the experimental observations of the ionosphere collected in the past years to assess the performance of climatological ionosphere models, with the focus on scintillation models, in order to evaluate their ability to properly support future needs, to identify weak areas if any, to propose recommendations for improvements and to implement these improvements whenever possible in existing models. This work focuses on the capabilities of GNSS-R techniques to characterize ionospheric scintillation, notably at low and high latitudes., Peer Reviewed, Postprint (published version)

Radio-Frequency Interference (RFI) and jamming are increasing problems for timing applications based on Global Navigation Satellite Systems (GNSS). FENIX-lite is a real-time pre-correlation anti-jamming system designed to provide increased resilience against RFI/jamming in critical GNSS-enabled applications. This work aims to evaluate the combined performance of FENIX-lite and a timing setup composed by two GNSS disciplined oscillators named DOWR. The results show that FENIX provides an anti-jamming resilience of 10-30 dB, at the expense of introducing a small bias and an additional jitter of 2-4 ns., Peer Reviewed, Postprint (published version)

Ships and ice monitoring is of key importance in numerous applications, such as maritime traffic control, prevention of illegal activities, climate change studies, and maritime security. In this work, the feasibility of near real-time ocean target detection from a constellation of spaceborne Global Navigation Satellite System-Reflectometry (GNSS-R) images is demonstrated by addressing the two following points: 1) simulation of the revisit time allowed by constellations of GNSS-R instruments; 2) derivation and implementation of an ocean target detector aimed at identifying inhomogeneous features inside the delay-Doppler map. The revisit time is computed by simulating a realistic mission as a function of the constellation size and the number of receiving channels of the GNSS-R instrument. The proposed ocean target detection algorithm consists of four steps - pre-processing, pre-screening, selection, and geolocation - and is validated using actual U. K. TechDemoSat-1 data., Peer Reviewed, Postprint (published version)

Satellite networks are expected to become an integral part of upcoming 5G systems. In this regard, the adoption of 5G mainstream softwarisation technologies such as Software Defined Networking (SDN) and Network Function Virtualization (NFV) arises as a necessary step in the evolution of satellite ground segment systems (e.g. satellite gateways and terminals). This softwarisation would allow satellite communications services to be delivered in a more flexible, agile and cost-effective manner than done today. The applicability of NFV and SDN technologies in the satellite ground segment has been researched by H2020 VITAL project in the context of combined terrestrial-satellite networks. This extended abstract outlines the scope of two case studies from VITAL project outcomes that will be presented at WWRF39., Peer Reviewed, Postprint (published version)

This paper investigates a novel application of Global Navigation Satellite System-Reflectometry (GNSS-R) in the fields of maritime surveillance and safety, and climate change analysis, namely sea target detection in near real-time. Potentialities of the recent GNSS-R technology in the detection of targets over the sea (large ships, sea ice sheets) in near real-time are explored by: 1) computing the revisit time achieved with constellations of GNSS-R satellites; 2) deriving, implementing and testing a sea target detection algorithm. The global average revisit time is evaluated by mission simulation in two realistic scenarios and is shown as a function of the number of parallel receiver channels and the number of GNSS-R satellites in orbit. The sea target detection algorithm consists of four steps - pre-processing, pre-screening, selection, and geolocation - and is tested using actual UK TechDemoSat-1 data., Peer Reviewed, Postprint (published version)

This work reviews and analyses potentially relevant technologies to ensure that the gaps and stakeholder needs for sea ice products are covered. Each variable related to sea ice that presenting gaps using the European EO infrastructure on the horizon (2020-2030) is revised according the stakeholder requirements, together with the feasibility of deploying available technologies on small satellites. A survey of instruments oriented towards sea ice observations in the past and current is presented. Based on this survey technological capabilities in terms of the spatial resolution, swath, mass, power, and data rate are obtained. In order to identify the technologies, numerical scores are assigned based on instrument capabilities. This works concludes with a set of the technologies compatible with small platforms, with the objective to complement the sea ice data products of Copernicus Services., Peer Reviewed, Postprint (published version)

Classical GNSS positioning in urban environments presents a variety of problems such as satellite signal blockage, reflection and fading, mainly caused by buildings. These issues reduce the number of available satellites, introduce distance biases into the signal path and lower their SNR, compromising the accuracy of the position solution obtained. The use of 3D city models alongside GNSS data enables the constructive usage of these problems. Signal reflections can be predicted in order to compensate the distance bias. Furthermore, a score can be assigned to candidate positions by comparing the expected signal characteristics to those of the actual received signals. Image similarity methods are also made possible, based on comparing user images to the 3D models to infer their real position. This thesis presents three main contributions: Firstly, an algorithm to obtain sky visibility data (Building Boundaries, or BB) from 3D models. Secondly, an implementation of an already established positioning method, Shadow Matching. Finally, the design and implementation of a new method, Artificial Photo Matching, which uses user images and BB data to obtain a position solution. The theory and implementation behind these techniques is presented, and their results discussed., El posicionamiento por GNSS clásico en entornos urbanos presenta diversos problemas, como bloqueo, reflexión y desvanecimiento de las señales de satélite. Estos impedimentos reducen el número de satélites disponibles, introducen un sesgo en la distancia recorrida por las señales, y disminuyen su SNR, comprometiendo la precisión de la posición estimada. El uso de modelos en 3D de ciudades, en combinación con datos de GNSS, permite un uso constructivo de estos problemas. Además, se pueden asignar puntuaciones a posiciones candidatas según el grado de similitud entre las señales que se espera recibir y la que realmente llega al receptor. Métodos basados en la comparación de imágenes también son posibles, basados en el parecido de las imágenes del usuario respecto al modelo 3D con tal de inferir su posición. Esta tesis presenta tres contribuciones principales: Primero, un algoritmo para obtener datos de visibilidad del cielo (Building Boundaries o BB) a partir de modelos 3D. Después, una implementación de un método ya establecido, Shadow Matching. Finalmente, el diseño e implementación de un nuevo método, Artificial Photo Matching, que usa imágenes y BBs con tal de estimar la posición. La teoría y implementación detrás de estas técnicas es presentado, y sus resultados comentados., El posicionament per GNSS clàssic, en entorns urbans, presenta diversos problemes, com bloqueig, reflexió i esvaniment dels senyals dels satèl·lits. Aquests impediments limiten el nombre de satèl·lits disponibles, incrementen la distància recorreguda pel senyal i en baixen la SNR, degradant la precisió de la posició estimada. L’ús de models en 3D de les ciutats, en combinació amb dades de GNSS, permet fer un ús constructiu d’aquests problemes. Les reflexions dels senyals poden ser predites per tal de compensar l’esbiaix introduït. A més a més, es poden assignar puntuacions a posicions candidates segons el grau de similitud entre la senyal que s’espera rebre i la que realment arriba al receptor. Mètodes basats en la comparació d’imatges també són possibles, basades en la ressemblança de les imatges de l’usuari respecte al model 3D per tal d’inferir la seva posició. Aquesta tesi presenta tres contribucions principals: Primer, un algorisme per obtenir dades de visibilitat del cel (Building Boundaries o BB) a partir de models 3D. Després, una implementació d’un mètode ja establert, Shadow Matching. Finalment, el disseny i implementació d’un nou mètode, Artificial Photo Matching, que fa servir imatges de l’usuari i BBs per tal d’estimar la posició. La teoria i implementació al darrere d’aquestes tècniques és presentada, i els resultats obtinguts comentats.

This paper discusses the unambiguous estimation of high-order BOC signals in the cloud based on signal snapshots gathered by low-end SDR receivers. In particular, the sensitivity and distortion problems are introduced, assessing the probability of false lock when using a conventional ML-based estimator (based on the search of the absolute maximum of the cross-correlation function) and a post-correlation ML-based estimator exploiting the a priori known distortion of the cross-correlation function introduced by the filtering stage of the SDR receiver. The simulation results show that, while distortion issues can be handled, sensitivity remains a problem at low C/No conditions and when limited snapshot lengths are considered., Peer Reviewed, Postprint (published version)

gLAB is a free open-source software to process GNSS data. The first release of this software package allows full processing capability of GPS data, and partial han- dling of Galileo and GLONASS data., gLAB is a free open-source software to process GNSS data. The first release of this software package allows full processing capability of GPS data, and partial handling of Galileo and GLONASS data. EGNOS is the european satellite augmentation system which provides integrity and accuracy to GNSS positioning. This upgrade will make gLAB one of the few free and open source applications able to process EGNOS data., gLAB es un software gratuito de código abierto para procesar datos GNSS. La primera versión de este paquete de software permite la capacidad de procesamiento completo de datos GPS y la manipulación parcial de datos de Galileo y GLONASS. EGNOS es el sistema europea de aumentación por satélite que proporciona integridad y exactitud en posicionamiento GNSS. Esta actualización hará que gLAB una de las pocas aplicaciones de código libre y abierto capaces de procesar datos de EGNOS., gLAB és un programari gratuït de codi obert per processar dades GNSS. La primera versió d'aquest programa permet la capacitat de processament complet de dades GPS i la manipulació parcial de dades de Galileo i GLONASS. EGNOS és el sistema europeu d'augmentació per satèl·lit que proporciona integritat i exactitut en posicionament GNSS. Aquesta actualització farà que gLAB sigui una de les poques aplicacions de codi lliure i obert capaços de processar dades de EGNOS.

Introduction: Satellite navigation systems are widely used for today's high accuracy applications demanding the most accurate ranging information obtainable, which is the carrier phase observable. Before the carrier phase observable can be utilized as a range information its inherent integer cycle ambiguity must be resolved. Unfortunately, high dynamics, shadowing and multipath may cause cycle-slips, i.e. jumps of the carrier phase observable by an integer multiple of wavelengths. Any cycle-slip if remained undetected would deteriorate the high ranging and positioning accuracy. Proposal: The objective of this Master Thesis is to design novel algorithms for cycle-slip detector, which must be implemented in a real-time algorithm to detect the cycle-slips for multi-frequency GNSS signals. Moreover, the detector must work either with GPS and Galileo satellite constellations. An efficient validation must be done, also including simulations to ensure the reliability of the entire algorithm.

In this project a GPS receiver will be implemented using a software defined radio. It will then be tested in static and low dynamic conditions using real GPS signals. Then, after a literature review, the tracking loop filters will be properly modified so as to be able to track the signals in high dynamic scenarios. Finally, using a signal generator that can mimic orbital conditions (LEO), synthetic signals will be generated and the performance of the software defined radio navigation receiver will be tested.