International Competition for Satellite-Based Navigation System Services

The goal of this work is to review the current state of Global Navigation Satellite System (GNSS) development and its potential impact on the social, economic, and political dynamics of the various states fielding the systems. The most recognizable GNSS is the US GPS. It is the only operational system functioning at the time of this writing and has become part of the global commons. GPS, by virtue of its uniqueness, is considered the \u27gold standard\u27 of satellite based positioning, navigation, and timing systems. This uniqueness has also enabled the US to fully capitalize on the sizable economic dividends gained by the US technology sector from the development and sales of GPS user equipment and services. This work argues that the emergence of three global peer competitors to GPS is going to usher in a changed international relations environment for those new players. The economic implications go beyond a simple return on investment and could represent the continued space science and technical competitiveness of these states or not. The international political ramifications of the success or failure of the particular GNSSs could have a greater impact on the current international order than has been previously considered. The European Union, Russia, and China have become inexorably locked in a contest of domestic political will to field the next generation of GNSS in order to free themselves from US GPS domination and at the same time gain economic advantage over the other in space system technologies. Concurrently, the US is endeavoring to field the next generation of GPS and maintain its dominance in the associated technologies linked to GPS

A Portuguese Case Study

There is a high national dependency on Position, Navigation and Timing (PNT) Systems for several individuals, services and organisations that depend on this information on a daily basis. Those who rely on precise, accurate and continuous information need to have resilient systems in order to be highly efficient and reliable. A resilient structure and constantly available systems makes it easier to predict a threat or rapidly recover in a hazardous environment. One of these organisations is the Portuguese Navy, whose main purposes are to combat and maintain maritime safety. In combat, resilient PNT systems are needed for providing robustness in case of any threat or even a simple occasional system failure. In order to guarantee maritime safety, for example in Search and Rescue Missions, the need of PNT information is constant and indispensable for positioning control. The large diversity of PNT-dependent equipment, developed over the last two decades, is a valid showcase for the high GPS dependency that is seen nowadays – which is vulnerable to various factors like interference, jamming, spoofing and ionospheric conditions. The recent interest over integrated PNT system resolutions is related to the search for redundancy, accuracy, precision, availability, low cost, coverage, reliability and continuity. This study aimed to build a current PNT Portuguese picture based on Stakeholder Analysis and Interviews; assess the vulnerability of those who depend mainly on GPS for PNT information and, find out what the next steps should be in order to create a National PNT Strategy.Existe uma elevada dependência nacional em sistemas de Posição, Navegação e Tempo (PNT) por parte de diversos indivíduos, serviços e organizações que dependem desta informação no seu dia-a-dia. Todos os que dependem de informação precisa, exata e contínua, necessitam de ter sistemas resilientes para que sejam altamente eficientes e fiáveis. Uma estrutura resiliente e sistemas continuamente disponíveis facilitam a previsão de possíveis ameaças ou a expedita recuperação da funcionalidade, em ambientes hostis. Uma destas organizações é a Marinha Portuguesa cujas funções principais são o combate, a salvaguarda da vida humana no mar e a segurança marítima e da navegação. Para o combate, são necessários sistemas PNT, resilientes, que ofereçam robustez em caso de uma simples ameaça ou falha temporária dos sistemas. Por forma a ser possível cumprir a missão, a necessidade de ter informação PNT, fidedigna e atualizada, é constante e indispensável para o controlo preciso e exato da posição. Uma unidade naval, por forma a permanecer continuamente no mar, manter a sua prontidão, treinar a sua guarnição ou ser empenhada num cenário de guerra, necessita de saber, com confiança e sem erros, a sua posição e referência de tempo. A grande diversidade de sistemas dependentes de informação PNT, desenvolveu-se em larga escala nas últimas duas décadas e sustenta cada vez mais a alta dependência do GPS, que é vulnerável a diversas fontes de erro, tais como interferência, empastelamento, mistificação e condições ionosféricas. Atualmente, o elevado interesse na criação de sistemas PNT integrados está associado à procura da redundância, exatidão, precisão, disponibilidade, baixo custo, cobertura, fiabilidade e continuidade. Este estudo teve como objetivos construir o panorama atual, em Portugal, ao nível dos Sistemas PNT, baseando-se numa análise de Stakeholders e entrevistas; avaliar a vulnerabilidade de organizações e serviços que dependam exclusivamente do GPS como fonte de informação PNT; e propor um possível caminho para que seja possível criar uma Estratégia PNT Naciona

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

GNSS Signal Quality Evaluation in Finland. Preliminary Study

This is the Final Report describing the GNSS-Signal Quality Evaluation in Finland (GLAS) –Preliminary Study project implementation. The project duration was from 1st October, 2016 – 28th February, 2017 and included identification of end-users, user requirements, initial service definition, and proof-of-concept demonstrator. This report also briefly describes the project structure and the future project plan. Section 1, 2, and 3 are an introduction to this document and the GLAS project. It describes the project scope and schedule for the first phase of activity, including a brief discussion about future phases of the project. Section 4 presents an executive summary of the report covering the most significant conclusions from this study. Section 5 lists the end-user groups and example end-users identified in the stakeholder analysis. This list was essential for inviting respondents to the project web-survey. Section 6 describes the results and conclusions of this web-survey – indicating the expectations and requirements of end-users. The complete web-survey results are provided in Appendix 3. Section 7 describes the conclusions from the detailed in-person interviews conducted with 4 (expert) end-users to know better their expectations and opinions. The detailed transcripts of the interviews are presented in Appendix 1. Section 8 presents conclusions from the comparative study of state-of-the-art services similar to GLAS-service available globally. The comparative table is provided in Appendix 2. Section 9 describes the FinnRef reference GNSS network and its capabilities, because that is envisaged as one of the data sources for the proposed service. Section 10 compiles all the information from previous Sections to offer an initial service definition for the GLAS-service based on which the first roll-out version of the service will be implemented. Finally, Section 11 describes briefly the proof-of-concept demonstrator service implemented as a prototype of the proposed GLAS-servic

PERFORMANCE EVALUATION OF LOW-COST PRECISION POSITIONING METHODS FOR FUTURE PORT APPLICATIONS

In recent times, a lot of research has been conducted to improve the accuracy of various positioning systems. The motivation behind this trend is to ensure high quality GNSS services for various applications. In particular, emphasis has been placed on improving the level of accuracy of consumer grade GNSS receivers. Significant improvements in the quality of signal reception of these receivers would enable low-cost solutions for asset management in for example, harbor areas. Research in Receiver Autonomous Integrity Monitoring - Fault Detection and Exclusion (RAIM-FDE) algorithms give users the ability to exclude satellites with degraded signals, hereby improving the performance of the GNSS solution. This research investigates and evaluates the performance of various customer grade GNSS positioning systems intended for port applications. Various high precision techniques such as Precise Point Positioning and Real-Time Kinematic were conducted and accuracy levels were noted on Multi-band receivers, Single frequency receivers, and GNSS-enabled smartphone. Our final conclusion suggests optimal low-cost GNSS solutions for asset monitoring and management

Alternatives for Navigating Small Unmanned Air Vehicles without GPS

Considering the increased reliance on GPS navigation for the Army’s Unmanned Aircraft Systems, adversaries have invested in capabilities to deny our systems access to genuine GPS signals. Although significant effort has been put forth in the areas of anti-jamming and anti-spoofing in GPS receivers, a need for alternative navigation methods in a GPS denied environment has grown in importance. This report outlines the recommendation and analysis completed for Mr. Lars Ericsson of the Army Project Manager Unmanned Aircraft Systems (PM-UAS).  The report includes background research in the domain space, comprehensive stakeholder analysis, derived system requirements and functional requirements, ending with alternative generation, value scoring, costing, and provided findings for a recommended alternative for future consideration. 

Variance Reduction of Sequential Monte Carlo Approach for GNSS Phase Bias Estimation

Global navigation satellite systems (GNSS) are an important tool for positioning, navigation, and timing (PNT) services. The fast and high-precision GNSS data processing relies on reliable integer ambiguity fixing, whose performance depends on phase bias estimation. However, the mathematic model of GNSS phase bias estimation encounters the rank-deficiency problem, making bias estimation a difficult task. Combining the Monte-Carlo-based methods and GNSS data processing procedure can overcome the problem and provide fast-converging bias estimates. The variance reduction of the estimation algorithm has the potential to improve the accuracy of the estimates and is meaningful for precise and efficient PNT services. In this paper, firstly, we present the difficulty in phase bias estimation and introduce the sequential quasi-Monte Carlo (SQMC) method, then develop the SQMC-based GNSS phase bias estimation algorithm, and investigate the effects of the low-discrepancy sequence on variance reduction. Experiments with practical data show that the low-discrepancy sequence in the algorithm can significantly reduce the standard deviation of the estimates and shorten the convergence time of the filtering

Helmert Variance Component Estimation for Multi-GNSS Relative Positioning

The Multi-constellation Global Navigation Satellite System (Multi-GNSS) has become the standard implementation of high accuracy positioning and navigation applications. It is well known that the noise of code and phase measurements depend on GNSS constellation. Then, Helmert variance component estimation (HVCE) is usually used to adjust the contributions of di¿erent GNSS constellations by determining their individual variances of unit weight. However, HVCE requires a heavy computation load. In this study, the HVCE posterior weighting was employed to carry out a kinematic relative Multi-GNSS positioning experiment with six short-baselines from day of year (DoY) 171 to 200 in 2019. As a result, the HVCE posterior weighting strategy improved Multi-GNSS positioning accuracy by 20.5%, 15.7% and 13.2% ineast-north-up(ENU) components, compared to an elevation-dependent (ED) priori weighting strategy. We observed that the weight proportion of both code and phase observations for each GNSS constellation were consistent during the entire 30 days, which indicates that the weight proportions of both code and phase observations are stable over a long period of time. It was also found that the quality of a phase observation is almost equivalent in each baseline and GNSS constellation, whereas that of a code observation is different. In order to reduce the time consumption off the HVCE method without sacrificing positioning accuracy, the stable variances of unit weights of both phase and code observations obtained over 30 days were averaged and then frozen as a priori information in the positioning experiment. The result demonstrated similar ENU improvements of 20.0%, 14.1% and 11.1% with respect to the ED method but saving 88% of the computation time of the HCVE strategy. Our study concludes with the observations that the frozen variances of unit weight (FVUW) could be applied to the positioning experiment for the next 30 days, that is, from DoY 201 to 230 in 2019, improving the positioning ENU accuracy of the ED method by 18.1%, 13.2% and 10.6%, indicating the effectiveness of the FVUW.Peer ReviewedPostprint (published version

Evaluation of earth rotation parameters from modernized GNSS navigation messages

Modernized navigation messages of global navigation satellite systems like GPS CNAV include earth rotation parameters (ERPs), namely the pole coordinates and UT1-UTC (∆UT1) as well as their rates. Broadcast ERPs are primarily needed for space-borne GNSS applications that require transformations between earth-fixed and inertial reference frames like navigation in earth orbit as well as to the moon. Based on a global tracking network of 23 stations, broadcast ERP values are obtained for the global systems GPS and BeiDou as well as the regional QZSS and IRNSS. Subsequent data sets at daily intervals show polar motion discontinuities of 0.4 to 0.7 mas for GPS, QZSS, and IRNSS, whereas BDS is worse by a factor of about two. Discontinuities in ∆UT1 range from 0.17 to 0.45 ms. External comparison with the C04 series of the International Earth Rotation and Reference Systems Service results in polar motion RMS differences of 0.3 to 1.0 mas and ∆UT1 differences of about 0.13 ms for GPS, QZSS, and IRNSS. Due to less frequent update intervals, BDS performs worse by a factor of 2 – 4. In view of the current GNSS-based positioning errors at geostationary or even lunar distances, the accuracy of GPS, QZSS, and IRNSS broadcast ERPs is sufficient to support autonomous spacecraft navigation without the need for external data