DESIGN AND ASSESSMENT OF A LEO GNSS MINICONSTELLATION FOR POSITIONING, NAVIGATION, AND TIMING (PNT)

Recently, there has been a resurgent demand in the United Arab Emirates for more accurate positioning, navigation, and timing signals, especially for some targeted applications such as autonomous vehicles and flying taxis. The existing Global Navigation Satellite Systems (GNSS) provide real-time positioning accuracy for up to several meters, while the targeted applications require fast convergence of centimeterlevel positioning accuracy. Recent studies have shown that transmitting GNSS signals from a Low Earth Orbit (LEO) instead of a Medium Earth Orbit (MEO) would enhance positioning accuracy. The main objective of this thesis is to design and simulate an optimum scenario of a mini-LEO constellation transmitting GNSS signals in LEO and assess its performance using a GNSS simulator tool. The second objective is to evaluate the performance of a ground-based GNSS receiver receiving GNSS signals from LEO regarding the receiver’s time to lock, locking period, continuity, Position Dilution of Precision (PDOP) and 3D positioning accuracy. The final objective is to compare the performance of the simulated mini-LEO GNSS constellation with the existing MEO GPS and Galileo. Skydel GNSS simulator tool, single frequency L1/E1 ublox receiver, Systems Tool Kit (STK), and u-center software were used to conduct this research. The best simulated LEO scenario had a design consisting of 35 satellites at 800 km altitude, distributed into 5 planes, with 7 satellites in each plane, the planes were 45° apart and the satellites were 30° in each plane. The results showed a range of PDOP values from 2.1 to 3.3, 3D positioning accuracy of 5.86 m, and the time the receiver took to lock was about 1 minute with a maximum locking period of 3 minutes and with no continuity. The results obtained from the simulated LEO constellation assessed using the ublox receiver were no better than those of the simulated MEO GPS and Galileo. The main reason behind the obtained results is that the current GNSS receivers are not designed to cope with the higher dynamics of the satellites in LEO

Position, velocity and time measurement with multiple constellation data from GPS, GALILEO, GLONASS and BEIDOU

Il presente lavoro si propone di illustrare la teoria, il metodo e le modalità del calcolo della PVT, ovvero della posizione, della velocità e del sincronismo temporale, di un utente sulla Terra o di un satellite in orbita bassa (dotato di ricevitore multiGNSS), utilizzando un software integrato che sfrutti tutti i segnali provenienti da tutte le costellazioni a copertura globale in quel momento visibili. Nel caso presente si sono utilizzati i segnali da GPS, Galileo, GLONASS e BeiDou, rilevati grazie ad un ricevitore fornito dall'Università di Padova (STONEX S580), sia per la determinazione della posizione, sia per implementare il calcolo della velocità attraverso l'effetto Doppler. Questo lavoro, in futuro, potrebbe portare a contributi nello sviluppo di tecnologie innovative in molti settori, quali: navigazione autonoma e trasporti, difesa e aerospazio, agricoltura e molti altri.This work intends to outline the theory and the methods for the computation of position, velocity and time (PVT) of a user on the surface of the Earth or of a LEO satellite (Low Earth Orbit). An integrated software written in MATLAB and PERL has been used; it processes all the signals transmitted by all the constellations visible in that precise moment and in that precise place. The software's core uses the Weighted Least Squares algorithm, which permits the efficient computation of position, speed, timing and tropospheric delay in a few iterations. In this thesis, signals from GPS, Galileo, BeiDou and GLONASS have been used, specifically for the computation of the speed, which is calculated from the Doppler Effect. These signals were detected through a receiver STONEX Cube-a S580 provided by the University of Padua. A good precision in determination of both positioning and speed has been achieved and also the PNT of a LEO satellite (Sentinel 3A) has been determined successfully, using data also to study J2 perturbations on the orbit. The principal aim of this thesis is to provide an efficient and precise software able to process pseudorange and Doppler shift multi-constellation data, to enhance, in its future evolutions, the precise positioning of a receiver on Earth's surface and in orbit, with interesting applications in many different fields such as defence, transportations and automotive, attitude determination in space and many others

Software Simulator and Signal Analysis for Galileo E5 band Signals

Galileo is the European Global Navigation Satellite System (GNSS) that aims at providing high availability, increased accuracy, and various location services under the civilian control. Four in-orbit validation satellites have already been launched till date and the system is estimated to be fully deployed by the year 2020. The Galileo navigation signals are transmitted at four frequency bands, which are named E5a, E5b, E6, and E1 bands. The signal of interest in this thesis is Galileo E5a band and Galileo E5b band signals. Signal acquisition and signal tracking are the main functions in a GNSS receiver. Acquisition identifies all the visible satellites and estimates the coarse values of carrier frequency and code phase estimates of the satellite signal. Tracking refines the coarse carrier frequency and code phase estimates, and keeps track of the satellite. The objective of this thesis has been to design and implement Galileo E5a and E5b signals receiver which can acquire all the visible E5a and E5b signals and which gives coarse estimate of carrier frequency and code phase. Such a receiver has been successfully designed in Matlab starting from the Matlab initial files provided by the Finnish Geodetic Institute (FGI) provided tool. In this thesis, two different software implementations are analyzed: 1) The acquisition and tracking of simulated Galileo E5a signals generated in the Matlab Simulink E1-E5 model; and 2) The acquisition of real-time Galileo E5b signals received from the satellite provided by Finnish Geodetic Institute (FGI), Masala, Finland. In the Simulink implementation, the whole E5 signal is generated and propagated through different channel profiles. The received signals are tested with acquisition and tracking and the results are compared for different channel profile and Carrier-to-Noise density ratio. Similarly, the real-time Galileo signals from four satellites now available on sky from the Galileo constellation were received and performed acquisition. In both implementations, a sharp triangular peak was observed at the rough frequency and code phase estimates, proving that the Galileo E5a/b signals can be indeed acquired correctly with the implemented simulator

Universal-SBAS: A worldwide multimodal standard

This paper describes a generalisation of the aeronautical GNSS Space Based Augmentation System (SBAS) air interface, in a true worldwide multimodal standard named Universal S-BAS. Examples of usages of this multifrequency future standard are presented in the area of science and precise positioning, timing, security, robust positioning, maritime and reflectometry applications

Global and Regional Navigation Satellite Systems: Security and Defense Applications and Intentional Threats against them

Η δορυφορική πλοήγηση είναι μία διαστημική ικανότητα που παρέχει υπηρεσίες σχετικές με πληροφορίες για τη θέση, την ταχύτητα και τον χρόνο σε χρήστες εξοπλισμένους με κατάλληλους δέκτες και που σήμερα έχει μεγάλη επιρροή στην καθημερινή μας ζωή. Επί του παρόντος, τέσσερα παγκόσμια δορυφορικά συστήματα πλοήγησης με παγκόσμια κάλυψη βρίσκονται σε λειτουργίαˑ επιπλέον, υπάρχουν δύο περιφερειακά δορυφορικά συστήματα πλοήγησης που καλύπτουν μόνο συγκεκριμένες περιοχές. Σε αυτή τη διπλωματική εργασία περιγράφονται η δορυφορική πλοήγηση και οι βασικές αρχές λειτουργίας της. Παρουσιάζονται τα παγκόσμια και τα περιφερειακά δορυφορικά συστήματα πλοήγησης, καθώς και μία τεχνική σύγκριση μεταξύ αυτών των συστημάτων. Αυτή η διπλωματική εργασία κάνει επίσης μία συζήτηση για τις εφαρμογές της δορυφορικής πλοήγησης που αφορούν σε θέματα ασφάλειας και άμυνας, τα οποία είναι πολύ σημαντικά και στους δύο τομείς, τον στρατιωτικό και τον πολιτικό. Παρουσιάζονται οι σκόπιμες απειλές εναντίον των δορυφορικών συστημάτων πλοήγησης, δηλαδή οι παρεμβολές θορύβου και παραπλάνησης του σήματος αυτών των συστημάτων και συζητούνται οι πιο σημαντικές τεχνικές ανίχνευσης και μείωσης αυτών των απειλών. Τα συμπεράσματα της διπλωματικής εργασίας επικεντρώνονται στη βελτίωση της απόδοσης των δορυφορικών συστημάτων πλοήγησης και στην ελάττωση της τρωτότητας αυτών των συστημάτων απέναντι στις σκόπιμες παρεμβολές εναντίον τους.Satellite navigation is a space capability that provides positioning, velocity and time information to users equipped with the suitable receiver and today has a significant influence on everyday life. Currently, four global navigation satellite systems with global coverage are operational; furthermore, two regional navigation satellite systems cover only specific areas. In this master thesis satellite navigation and its basic principles of operation are described. The global and the regional navigation satellite systems as well as a technical comparison between these systems are presented. This thesis also discusses satellite navigation applications concerning security and defense issues, which are of great importance for both military and civil sectors. The intentional threats against the navigation satellite systems, that is, jamming and spoofing interference of the signal of these systems, are presented and some of the most important techniques for detection and mitigation of these threats are discussed. The conclusions of this thesis concentrate on improving the performance of the navigation satellite systems, and reducing the vulnerability of these systems towards the intentional interference against them

Multi-GNSS Precise Point Positioning Software Architecture and Analysis of GLONASS Pseudorange Biases

With expanding satellite-based navigation systems, multi-Global Navigation Satellite System (GNSS) Precise Point Positioning (PPP) presents an advantage over a single navigation system, which improves position accuracy and enhances availability of satellites and signals. The York GNSS PPP software was developed using C++ in the Microsoft.Net platform to utilize the existing multi-GNSS satellite constellations based on the software processor used by the Natural Resources Canada (NRCan) PPP online service. The software was built as a robust, scalable, modular tool that meets the highest of scientific standards compared to existing online PPP engines.There exists a correlation between receiver stations from heterogeneous networks, such as the IGS, in GNSS PPP processing and the increase in magnitude of the pseudorange and carrier-phase biases in both GPS + GLONASS and GLONASS-only PPP solutions. The correlation is due to mixed receiver and antenna hardware as well as firmware versions. Unlike GPS, GLONASS observations are affected by the Frequency Division Multiple Access (FDMA) satellite signal structure, which introduces inter-frequency channel biases and other system biases. The GLONASS pseudorange inter-channel frequency biases show a strong correlation with different receiver types, firmware versions and antenna types. This research estimated the GLONASS pseudorange inter-frequency channel biases using 350 IGS stations, based on 32 receiver types and 4 antenna types over a period of one week. An improvement of 19% was observed after calibrating for the pseudorange ICBs, in the horizontal components respectively, considering 20 minutes convergence period

Precise Point Positioning Augmentation for Various Grades of Global Navigation Satellite System Hardware

The next generation of low-cost, dual-frequency, multi-constellation GNSS receivers, boards, chips and antennas are now quickly entering the market, offering to disrupt portions of the precise GNSS positioning industry with much lower cost hardware and promising to provide precise positioning to a wide range of consumers. The presented work provides a timely, novel and thorough investigation into the positioning performance promise. A systematic and rigorous set of experiments has been carried-out, collecting measurements from a wide array of low-cost, dual-frequency, multi-constellation GNSS boards, chips and antennas introduced in late 2018 and early 2019. These sensors range from dual-frequency, multi-constellation chips in smartphones to stand-alone chips and boards. In order to be comprehensive and realistic, these experiments were conducted in a number of static and kinematic benign, typical, suburban and urban environments. In terms of processing raw measurements from these sensors, the Precise Point Positioning (PPP) GNSS measurement processing mode was used. PPP has become the defacto GNSS positioning and navigation technique for scientific and engineering applications that require dm- to cm-level positioning in remote areas with few obstructions and provides for very efficient worldwide, wide-array augmentation corrections. To enhance solution accuracy, novel contributions were made through atmospheric constraints and the use of dual- and triple-frequency measurements to significantly reduce PPP convergence period. Applying PPP correction augmentations to smartphones and recently released low-cost equipment, novel analyses were made with significantly improved solution accuracy. Significant customization to the York-PPP GNSS measurement processing engine was necessary, especially in the quality control and residual analysis functions, in order to successfully process these datasets. Results for new smartphone sensors show positioning performance is typically at the few dm-level with a convergence period of approximately 40 minutes, which is 1 to 2 orders of magnitude better than standard point positioning. The GNSS chips and boards combined with higher-quality antennas produce positioning performance approaching geodetic quality. Under ideal conditions, carrier-phase ambiguities are resolvable. The results presented show a novel perspective and are very promising for the use of PPP (as well as RTK) in next-generation GNSS sensors for various application in smartphones, autonomous vehicles, Internet of things (IoT), etc

Methods for Improving Performance in Consumer Grade GNSS Receivers

Viimeisten kolmen vuosikymmenen aikana satelliittinavigointi on kehittynyt ammatti ja sotilaskäyttäjien tekniikasta kaikkien saatavilla olevaksi tekniikaksi. Varsinkin viimeisen 15 vuoden aikana, kun vastaanottimet alkoivat pienentyä ja halpenivat, on lisääntynyt määrä yrityksiä, jotka toimittavat GPS-laitteita satoihin erilaisiin sovelluksiin. Kaikille moderneille tekniikoille on myös tyypillistä, että tutkimukseen ja siihen liittyvään vastaanottimien kehittämiseen on käytetty valtavasti rahaa, mikä on johtanut huomattavaan parantumiseen vastaanottimen suorituskyvyssä. GPS-vastaanottimien kehitystyön lisäksi uusien maailmanlaajuisten satelliittinavigointijärjestelmien, kuten venäläisen GLONASS, kiinalaisen BeiDou- ja eurooppalaisen Galileo-järjestelmien käyttöönotto tarjoaa entistä enemmän mahdollisuuksia suorituskyvyn parantamiseen. Sekä GPS että nämä uudet järjestelmät ovat myös ottaneet käyttöön uudentyyppisiä signaalirakenteita, jotka voivat tarjota parempilaatuisia havaintoja ja siten parantaa kaikkien vastaanottimien suorituskykyä. Lopuksi menetelmät, kuten PPP ja RTK, jotka aiemmin olivat varattu ammattikäyttäjille, ovat tulleet kuluttajamarkkinoille mahdollistaen ennennäkemättömän suorituskyvyn jokaiselle satelliittinavigointivastaanottimien käyttäjälle. Tässä opinnäytetyössä arvioidaan tämän kehityksen vaikutusta sekä suorituskykyyn että vastaanottimen arkkitehtuuriin. Työssä esitellään yksityiskohtaisesti FGI:ssä kehitetyn ohjelmistopohjaisen vastaanottimen, FGI-GSRx:n. Tämän vastaanottimen avulla on työssä arvioitu miten sekä uudet konstellaatiot että uudet nykyaikaiset signaalit ja niitten seurantamenetelmät vaikuttavat suorituskykyyn ja vastaanotin arkkitehtuuriin. Tämän lisäksi on arvioitu PPP- ja RTK-tarkkuuspaikannusmenetelmien vaikutus FinnRefCORS-verkkoa käyttäen useiden erityyppisten vastaanottimien kanssa, mukaan lukien kuluttajalaatuiset vastaanottimet. Tulokset osoittavat, että enemmän konstellaatioita ja signaaleja käytettäessä paikannusratkaisun tarkkuus paranee 3 metristä 1,4 metriin hyvissä olosuhteissa ja yli 10-kertaiseksi tiheästi rakennetuissa kaupungeissa, jossa käytettävissä olevien signaalien määrä kasvaa kertoimella 2 käytettäessä kolmea konstellaatiota. Uusia moderneja modulaatiotekniikoita, kuten BOC-modulaatiota, käytettäessä tulokset osoittavat Galileo-ratkaisun tarkkuuden paranevan lähes 25%:lla ja esitelty uusi signaalinkäsittelymenetelmä lisää tällaisen tarkkuuden saatavuutta 50%:sta lähes 100%:iin. Lopuksi tarkkuuspaikannusmenetelmien tulokset osoittavat, että 15 cm:n tarkkuus on saavutettavissa, mikä on merkittävä parannus verrattuna 1,4 metrin tarkkuuteen. Näiden parannusten saavuttamiseksi on olennaista, että itse vastaanotin on mukautettu hyödyntämään näitä uusia signaaleja ja konstellaatioita. Tämä tarkoittaa, että nykyaikaisten kuluttajamarkkinoiden vastaanottimien suunnittelu on haastavaa ja monissa tapauksissa ohjelmistopohjainen vastaanotin olisi parempi ja halvempi valinta kuin uusien mikropiirien kehittäminen.For the last three decades, satellite navigation has evolved from being a technology for professional and military users to a technology available for everyone. Especially during the last 15 years, since the receivers started getting smaller and cheaper, there has been an increasing number of companies delivering Global Positioning System (GPS) enabled devices for hundreds of different kind of applications. Typical for any modern technology, there has also been an enormous amount of money spent on research and accompanied receiver development resulting in an immense increase in receiver performance. In addition to the development efforts on GPS receivers the introduction of new global navigation satellite systems such as the Russian Globalnaja Navigatsionnaja Sputnikovaja Sistema (GLONASS), the Chinese BeiDou, and the European Galileo systems offers even more opportunities for improved performance. Both GPS and these new systems have also introduced new types of signal structures that can provide better quality observations and even further improve the performance of all receivers. Finally, methods like Precise Point Positioning (PPP) and Real Time Kinematic (RTK) that earlier were reserved for professional users have entered into the consumer market enabling never before seen performance for every user of satellite navigation receivers. This thesis will assess the impact of this development on both performance as well as on receiver architecture. The design of the software defined receiver developed at FGI, the FGI-GSRx, is presented in detail in this thesis. This receiver has then been used to assess the impact of using multiple constellations as well as new novel signal processing methods for modern signals. To evaluate the impact of PPP and RTK methods the FinnRef Continuously Operating Reference Station (CORS) network has been used together with several different types of receivers including consumer grade off the shelf receivers. The results show that when using more constellations and signals the accuracy of the positioning solution improves from3 meters to 1.4 meters in open sky conditions and by more than a factor 10 in severe urban canyons. For severe urban canyons the available also increases by a factor 2 when using three constellations. When using new modern modulation techniques like high order BOC results show an accuracy improvement for a Galileo solution of almost 25 % and the presented new signal processing method increase the availability of such an accuracy from 50 % to almost 100 %. Finally, results from precise point positioning methods show that an accuracy of 15 cm is achievable, which is a significant improvement compared to an accuracy of 1.4 m for a standalone multi constellation solution. To achieve these improvements, it is essential that the receiver itself is adapted to make use of these new signals and constellations. This means that the design of modern consumer market receivers is challenging and in many cases a software define receiver would be a better and cheaper choice than developing new Application Specific Integrated Circuit (ASIC)’s

The regime complex of global space governance : the international space politics of the 21st century

Post-Cold War trends in national space-capability building and the liberalization of the global space economy have expanded the concerns of states in international astropolitics from security as such to other issue areas, including safety, economic growth and social development, and sustainability. Since the beginning of the 21st Century, the constellation of international space regimes has continued to expand, while the global governing architecture has fragmented. Within a ‘regime complex’ analytical framework, this work presents two interpretive narratives of the strategic, functional and organizational aspects that explain the design and evolution of ‘the regime complex of global space security governance’ and ‘the GNSSs regime complex’. The case studies chart the dynamics of international space politics and analyze the growing structural fragmentation of the complex global scheme of space governance. An additional enabling factor such as innovation was identified as vital to reinforce the growth of regime complex in global space governance