Multi-band Multi-site GNSS RFI Monitoring Results after a Year of Operation

An international network of Radio Frequency Interference (RFI) monitoring stations covering all L-band Global Navigation Satellite System (GNSS) signals has provided large amounts of data on the occurrence rates and characteristics of the detected sources. As the stations are primarily deployed by roadways the measurements include a large number of Personal Privacy Device (PPD) style jammers as well as an unexpectedly large contingent of spurious emissions and co-authorized users. Important results include the high levels of variability in month-to-month activity levels of sites indicating that site survey activities must be conducted over longer periods to obtain accurate occurrence rate information.acceptedVersio

Theoretical Analysis of the Processof Doppler and Doppler Rate Estimation in Standard and High Sensitivity GNSS Receivers

Due to the capability of the Global Positioning System (GPS) to provide accurate, stablelong-term navigation information, the use of a GPS receiver as a velocity and accelerationsensor has gained an increasing research interest. Navigation and control, airbornegravimetry and integration with inertial navigation systems (INS) are just some of thepotential applications. GPS velocity and acceleration measurements are typically determined using Doppler and Doppler rate observations provided by the receiver carrier tracking loops. Thus, the finalquality of the velocity/acceleration measurements depends on the variance of the Dopplerand Doppler rate observations and on the approach used for the velocity/accelerationcomputation. It is therefore desirable to be able to predict the quality of Doppler andDoppler rate observations, not only for quality control and for estimating the uncertainty ofthis information, but also for properly weighting the measurements in the LS and KFsolution. This thesis introduces a cohesive analysis describing the noise propagation process from theinput of the carrier tracking loops to the final Doppler and Doppler rate estimates. Two different approaches used by GNSS receivers are considered namely the sequential carriertracking, including the standard and memory discriminator based approaches, and blockprocessing techniques. For each approach, a theoretical framework for Doppler estimationrelating the variance and biases of the Doppler estimates to C/N0, the user dynamics and thealgorithm parameters is introduced. Also, based on the proposed theoretical framework a new approach to loop filter designproviding control over the noise variance of the Doppler measurements is introduced.The developed theoretical framework and the proposed approach to loop filter design havebeen verified by performing a number of static and dynamic pedestrian-based field testsand simulations with the major focus on the environments with strong signal attenuationand multipath.PhD i elektronikk og telekommunikasjonPhD in Electronics and Telecommunicatio

Estudo das colocações lexicais nos sistemas linguísticos português e russo e o seu papel no ensino - aprendizagem do PLE

Dissertação de mestrado em Português Língua Não Materna (PLNM) - Português Língua Estrangeira (PLE) e Língua Segunda (PL2)O primeiro objetivo deste trabalho é definir o conceito de colocação lexical e determinar o lugar das colocações entre outras combinações lexicais de nível de fixidez variado. Assim, os métodos de definição deste fenómeno lexical são os seguintes: 1) analisar abordagens diferentes ao assunto; 2) estudar o conceito de colocação com uma perspetiva de comparação, usando classificações de combinações lexicais livres e restritas. O segundo objetivo deste estudo é realizar uma análise comparativa da língua portuguesa com a língua russa, do ponto de vista do conceito de colocação lexical, revelando as diferenças na composição e no uso de colocações. O método deste estudo é uma análise de exemplos concretos de colocações. Um outro objetivo é determinar o papel das colocações lexicais no ensino-aprendizagem de PLE para falantes russos. O estudo de colocações permite: 1) compreender que o ponto de partida para aprender uma língua estrangeira não é a palavra, mas sim a combinação lexical; 2) desenvolver habilidades de combinar palavras; 3) aprender palavras novas; 4) aprender regras gramaticais. O objetivo final da dissertação é criar uma proposta do ensino de colocações lexicais portuguesas para falantes russos. Propomos como estratégias para os professores de PLE as segintes: 1) no caso de alunos universitários de faculdades de letras, associar aulas práticas de língua com aulas teóricas de linguística; 2) dividir os métodos de ensino de colocações segundo o princípio da existência de equivalentes; 3) compreender a importância de autodidática; 4) usar aulas de tradução no processo de ensino; 5) combinar o método tradicional gramática-tradução com outros métodos. Este trabalho é dedicado a professores e aprendentes russos de PLE e, neste contexto, serão estudados métodos de ensino de línguas estrangeiras e de materiais didáticos portugueses e russos para estudo de PLE.The main objective of this work is to define the concept of lexical collocation and determine the place of collocations among other lexical combinations of varied level of fixity. Thus the methods of definition of this lexical phenomenon are the following: 1) analyze different approaches to the subject; 2) study the concept of collocation with a prospective comparison, using classifications of free and restricted word combinations. The second objective of this research is to conduct a comparative analysis of the Portuguese language and the Russian language from the point of view of the collocational concept revealing the differences in the composition and usage of collocations. The method of this study is the analysis of the concrete examples of collocations. Another objective is to determine the role of lexical collocations in teaching and studying Portuguese as a foreign language (PFL) for native Russian speakers. Learning collocations permits: 1) understand that the starting-point for learning a foreign language is not a word but a lexical combination; 2) develop skills of combination of words; 3) learn new words; 4) learn grammar rules. The final objective of the thesis is to create a proposal of teaching lexical collocations in Portuguese for Russian speakers. The PFL teachers’ strategies should be the following: 1) in case of university students from the philological departments, associate the practical language lessons with the theoretical lessons in linguistics; 2) divide the methods of teaching collocations according to the principle of the existence of the equivalents; 3) understand the importance of self-education; 4) combine the traditional grammar-translation with other methods. This work is dedicated to teachers and learners of PFL and in this context the question is about the methods of teaching foreign languages and about Portuguese and Russian didactic materials for studying of PFL.Первой целью данной работы является определение понятия лексической коллокации и места коллокаций среди других словосочетаний разной степени устойчивости. Для определения данного лексического феномена используются следующие методы: 1) анализ различных подходов к предмету; 2) изучение понятия коллокации с последующим применением сравнений и использованием классификаций свободных и связанных словосочетаний. Второй целью данной работы является проведение сравнительного анализа португальского и русского языков с точки зрения понятия лексической коллокации и выявление различий в образовании и использовании коллокаций. Методом исследования в этой области является анализ конкретных примеров коллокаций. Ещё одной целью является определение роли лексических коллокаций в процессе обучения русскоговорящих студентов португальскому языку как иностранному (ПКИ). Изучение коллокаций позволяет: 1) понять, что отправной точкой в изучении иностранного языка является не слово, а словосочетание; 2) развить навыки комбинирования слов; 3) учить новые слова; 4) изучать грамматические правила. Конечная цель диссертации – предложить способ изучения лексических коллокаций для русскоговорящих. Стратегии, применяющиеся преподавателями ПКИ должны быть следующими: 1) в случае со студентами филологических факультетов университетов связывать практические языковые занятия с теоретическими занятиями по языкознанию; 2) разделять способы обучения в соответствии с принципом наличия эквивалентов; 3) понимать важность самостоятельного обучения; 4) использовать занятия по переводу в процессе обучения; 5) комбинировать традиционный грамматико- переводной метод с другими. Данная работа предназначена для русских преподавателей и студентов ПКИ, и в этом контексте речь идёт о методах обучения иностранным языкам и о португальских и русских дидактических материалах для изучения ПКИ

Loop Filters with Controllable Doppler Jitter for Standard and High Sensitivity GNSS Receivers

Standard tracking loops are usually designed by selecting the loop bandwidth that controls the variance of the phase observable. In this paper, a new approach for the loop filter design is introduced. The proposed methodology is based on the concept of Doppler bandwidth and provides control over the variance of Doppler frequency measurements. Doppler measurements reflect the relative motion between receiver and satellites and can be used to simplify the selection of the loop parameters that can be directly determined as a function of the user dynamics. Two different GNSS carrier tracking loop architectures are considered, namely standard and memory discriminator based tracking loops, and a design example is provided to show the effectiveness of the proposed approach.JRC.G.6-Security technology assessmen

Characterization of the GNSS RFI Threat to DFMC GBAS Signal Bands

This article presents analysis results from a long-term multi-site Global Navigation Satellite System (GNSS) Radio Frequency Interference (RFI) monitoring campaign in the context of Ground Based Augmentation System (GBAS) Dual Frequency Multi Constellation (DFMC) concept operation. GBAS resilience against unintentional RFI is an important area for investigation as the ground station receivers often must operate adjacent to high-traffic roads where chances of being affected by RFI are high. To be able to develop algorithms and reaction strategies necessary to ensure continuity and availability of service, knowledge of interference signal characteristics and frequency band/bands affected, as well as relative occurrence rates between the considered frequencies and frequency combinations, is necessary. The analysis presented in the article covers the prevalence and properties of the RFI events observed on the GPS L1 and L5 and the Galileo E1 and E5a frequency bands that are considered by the on-going DFMC GBAS concept development initiatives. Due to being spectrally adjacent, the observed event analysis is also carried out for the Galileo E5b and GLONASS G1 frequency bands. The article also addresses the issue of spectral occupancy distribution of the observed events and presents new interesting RFI event types captured during the considered monitoring period.publishedVersio

Automatic GNSS RFI Classification Challenges

This article describes the real-world challenges that are encountered when trying to automatically categorize and classify the radio frequency interference (RFI) events captured in the GNSS signal bands by an international network of monitoring stations covering all L-band navigation signals. While signals frequently fall into the often-discussed categories such as 'chirp', 'continuous wave', or 'wideband noise', there is a large and growing number of modulations encountered in reality, both intentional and unintentional. These bear varying degrees of resemblance to the aforementioned traditional categories. Work presented herein focuses on some of the main complications encountered when categorizing multiple years of GNSS RFI event data, and the algorithmic approaches used to proceed with classification in these conditions.publishedVersio

Implementation and Test of a Low Cost GBAS Subset Airborne Receiver Experimental Platform for UAVs

A Ground Based Augmentation System (GBAS) provides differential corrections to Global Navigation Satellite Systems (GNSS) using VHF Data Broadcast (VDB) Equipment. This paper discusses development and test of an experimental low cost single frequency (GPS L1) GBAS airborne subset receiver. The objective of the design is to serve as a research platform for implementation and testing of different measurement processing architectures and integrity monitoring algorithms suitable for new potential user types such as small Unmanned Aerial Vehicles (UAVs). Following a brief discussion of platform architecture and component selection, preliminary results from a field test carried out near to the Zurich airport with its operational GBAS Approach Service Type (GAST) C GBAS station are presented. We describe an experimental low cost prototype receiver to implement GBAS with adaptive carrier smoothing for a single frequency Global Positioning System (GPS) and VDB receiver. Our results demonstrate how low cost GNSS receiver sensitivity can be increased to make it more robust, and viable via additional signal analyses focused on the receiver RF block’s messages.publishedVersio

Differential ZTD estimation based on high spatial resolution NWP data for the Nordic countries

This paper contains results from a study where Numerical Weather Product (NWP) data provided by MET Norway are used to estimate the differential zenith tropospheric delay (dZTD) for an area covering Scandinavia, Finland and the Baltic countries. The NWP data have a high spatial resolution of 2.5 × 2.5 km, and the estimated dZTD for the grid positions allow for calculation of the tropospheric gradient on short baselines. The results give an indication of how large dZTD values that can be observed for baselines up to 20 km, and where the largest events are located within the coverage area. The motivation for this investigation is to better understand the characteristics of this phenomena and how it might impact high precision and/or high integrity GNSS-based navigation systems in these regions.acceptedVersio

Navigation Algorithm-Agnostic Integrity Monitoring based on Solution Separation with Constrained Computation Time and Sensor Noise Overbounding

Integrity monitoring (IM) in autonomous navigation has been extensively researched, but currently available solutions are mainly applicable to specific algorithms and sensors, or limited by linearity or 'Gaussianity' assumptions. This study investigates a Solution Separation (SS) based framework for universal IM, scalable to multi-sensor fusion as each hypothesis assumes a whole sensor measurement set as faulty. Architecturally we consider that: 1) multi sensor systems must account for various sensor noise models which lead to inconsistent estimates of uncertainties, 2) a module must be able to detect sensor failure or sensor noise mismodeling and suggest better bounds for the error, without being constantly conservative, 3) some algorithms are computationally heavy to monitor in the SS setting or the provided covariances cannot be interpreted in IM. A hybrid SS architecture can be practical, where some solutions are evaluated with a navigation algorithm with known characteristics, although the all-sensor-in solution is evaluated with the monitored algorithm. Experiments are run on filter and smoothing-based navigation algorithms. In addition, we experiment with hybrid SS monitoring and time-correlated noise to evaluate the appropriability of our framework in the context of the above-mentioned requirements. This is a novel framework in the IM domain, directly integrable in existing navigation solutions and, in our opinion, it will facilitate the quantification of the effect of different sensors in navigation safety.publishedVersio

GNSS-Denied Navigation using Direction of Arrival from Low-Cost Software Defined Radios and Signals of Opportunity

This paper describes a novel navigation system for outdoor navigation in conditions where reliable satellite navigation cannot be assumed. It is build around inexpensive of-the-shelf hardware and could be used with several different signal types, allowing flexibility in usage. The system is currently in a proof-of-concept stage, and this paper shows that there are promising preliminary results.acceptedVersio