P-RANSAC: An Integrity Monitoring Approach for GNSS Signal Degraded Scenario

Satellite navigation is critical in signal-degraded environments where signals are corrupted and GNSS systems do not guarantee an accurate and continuous positioning. In particular measurements in urban scenario are strongly affected by gross errors, degrading navigation solution; hence a quality check on the measurements, defined as RAIM, is important. Classical RAIM techniques work properly in case of single outlier but have to be modified to take into account the simultaneous presence of multiple outliers. This work is focused on the implementation of random sample consensus (RANSAC) algorithm, developed for computer vision tasks, in the GNSS context. This method is capable of detecting multiple satellite failures; it calculates position solutions based on subsets of four satellites and compares them with the pseudoranges of all the satellites not contributing to the solution. In this work, a modification to the original RANSAC method is proposed and an analysis of its performance is conducted, processing data collected in a static test

A New Relative Receiver Autonomous Integrity Monitoring Algorithm for Multiple Failures

authors' final manuscriptIn near future, GNSS GPS modernization, renewed GLONASS and a new Galileo signal will be available. And the accuracy of position solution will be better by courtesy of improved quality of ranging signal. As an expected accuracy is better, the threshold for failure will be reduced. As a result, the prior probability of failures could be larger than what is used now. Due to the increased prior probability of failures, probability of simultaneous multiple failures cannot be neglected any more. Furthermore there will be many more ranging sources makes it necessary to consider the possibility of simultaneous multiple failures. This paper develops and analyzes a new Relative Receiver Autonomous Integrity Monitoring (RRAIM) algorithm which can treat no only a single failure but also simultaneous multiple failures. A proposed algorithm uses measurement residuals and satellite observation matrices of several consecutive epochs for Failure Detection and Exclusion (FDE). It detects failures by monitoring the error vector itself instead of monitoring the projection of the error vector. The simulation results show that the algorithm is able to detect any instance of multiple failures which are not detected by the conventional RAIM algorithm.OAIID:oai:osos.snu.ac.kr:snu2012-01/104/0000003405/18SEQ:18PERF_CD:SNU2012-01EVAL_ITEM_CD:104USER_ID:0000003405ADJUST_YN:NEMP_ID:A000360DEPT_CD:446CITE_RATE:0FILENAME:Manuscript_HoYun.pdfDEPT_NM:기계항공공학부EMAIL:[email protected]:

Integrity Monitoring: From Airborne to Land Applications

Safety-critical applications in transportation require GNSS-based positioning with high levels of continuity, accuracy and integrity. The system needs to detect and exclude faults and to raise an alarm in the event of unsafe positioning. This capability is referred to as integrity monitoring (IM). While IM was considered until recently only in aviation, it is currently a key performance parameter in land applications, such as Intelligent Transport Systems (ITS). In this chapter the IM concepts, models and methods developed so far are compared. In particular, Fault Detection and Exclusion (FDE) and bounding of positioning errors methods borrowed from aviation (i.e. Weighted RAIM and ARAIM) are discussed in detail, in view of their possible adoption for land applications. Their strengths and limitations, and the modifications needed for application in the different context are highlighted. A practical demonstration of IM in ITS is presented

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

Integrity monitoring applied to the reception of GNSS signals in urban environments

L’intégrité des signaux GNSS est définie comme la mesure de la confiance qui peut être placée dans l’exactitude des informations fournies par le système de navigation. Bien que le concept d’intégrité GNSS a été initialement développé dans le cadre de l’aviation civile comme une des exigences standardisées par l’Organisation de l’Aviation Civile Internationale (OACI) pour l’utilisation du GNSS dans les systèmes de Communication, Navigation, et Surveillance / Contrôle du Trafic Aérien (CNS/ATM), un large éventail d’applications non aéronautiques ont également besoin de navigation par satellite fiable avec un niveau d’intégrité garanti. Beaucoup de ces applications se situent en environnement urbain. Le contrôle d’intégrité GNSS est un élément clé des applications de sécurité de la vie (SoL), telle que l’aviation, et des applications exigeant une fiabilité critique comme le télépéage basé sur l’utilisation du GNSS, pour lesquels des erreurs de positionnement peuvent avoir des conséquences juridiques ou économiques. Chacune de ces applications a ses propres exigences et contraintes, de sorte que la technique de contrôle d’intégrité la plus appropriée varie d’une application à l’autre. Cette thèse traite des systèmes de télépéage utilisant GNSS en environnement urbain. Les systèmes de navigation par satellite sont l’une des technologies que l’UE recommande pour le Service Européen de Télépéage Electronique (EETS). Ils sont déjà en cours d’adoption: des systèmes de télépéage pour le transport poids lourd utilisant GPS comme technologie principale sont opérationnels en Allemagne et en Slovaquie, et un système similaire est envisagé en France à partir de 2013. À l’heure actuelle, le contrôle d’intégrité GPS s’appuie sur des systèmes d´augmentation (GBAS, SBAS, ABAS) conçus pour répondre aux exigences de l’OACI pour les opérations aviation civile. C´est la raison pour laquelle cette thèse débute par une présentation du concept d’intégrité en aviation civile afin de comprendre les performances et contraintes des systèmes hérités. La thèse se poursuit par une analyse approfondie des systèmes de télépéage et de navigation GNSS en milieu urbain qui permets de dériver les techniques de contrôle d’intégrité GNSS les plus adaptées. Les algorithmes autonomes de type RAIM ont été choisis en raison de leur souplesse et leur capacité d´adaptabilité aux environnements urbains. Par la suite, le modèle de mesure de pseudodistances est élaboré. Ce modèle traduit les imprécisions des modèles de correction des erreurs d’horloge et d’ephemeride, des retards ionosphériques et troposphériques, ainsi que le bruit thermique récepteur et les erreurs dues aux multitrajets. Les exigences d’intégrité GNSS pour l’application télépéage sont ensuite dérivées à partir de la relation entre les erreurs de positionnement et leur effets dans la facturation finale. Deux algorithmes RAIM sont alors proposés pour l’application péage routier. Le premier est l’algorithme basé sur les résidus de la solution des moindres carrés pondérés (RAIM WLSR), largement utilisé dans l’aviation civile. Seulement, un des principaux défis de l’utilisation des algorithmes RAIM classiques en milieux urbains est un taux élevé d’indisponibilité causé par la mauvaise géométrie entre le récepteur et les satellites. C’est pour cela que un nouvel algorithme RAIM est proposé. Cet algorithme, basé sur le RAIM WLSR, est conçu de sorte à maximiser l’occurrence de fournir un positionnement intègre dans un contexte télépéage. Les performances des deux algorithmes RAIM proposés et des systèmes de télépéage associés sont analysés par simulation dans différents environnements ruraux et urbains. Dans tous les cas, la disponibilité du nouvel RAIM est supérieure à celle du RAIM WLSR. ABSTRACT : Global Navigation Satellite Systems (GNSS) integrity is defined as a measure of the trust that can be placed in the correctness of the information supplied by the navigation system. Although the concept of GNSS integrity has been originally developed in the civil aviation framework as part of the International Civil Aviation Organization (ICAO) requirements for using GNSS in the Communications, Navigation, and Surveillance / Air Traffic Management (CNS/ATM) system, a wide range of non-aviation applications need reliable GNSS navigation with integrity, many of them in urban environments. GNSS integrity monitoring is a key component in Safety of Life (SoL) applications such as aviation, and in the so-called liability critical applications like GNSS-based electronic toll collection, in which positioning errors may have negative legal or economic consequences. At present, GPS integrity monitoring relies on different augmentation systems (GBAS, SBAS, ABAS) that have been conceived to meet the ICAO requirements in civil aviation operations. For this reason, the use of integrity monitoring techniques and systems inherited from civil aviation in non-aviation applications needs to be analyzed, especially in urban environments, which are frequently more challenging than typical aviation environments. Each application has its own requirements and constraints, so the most suitable integrity monitoring technique varies from one application to another. This work focuses on Electronic Toll Collection (ETC) systems based on GNSS in urban environments. Satellite navigation is one of the technologies the directive 2004/52/EC recommends for the European Electronic Toll Service (EETS), and it is already being adopted: toll systems for freight transport that use GPS as primary technology are operational in Germany and Slovakia, and France envisages to establish a similar system from 2013. This dissertation begins presenting first the concept of integrity in civil aviation in order to understand the objectives and constraints of existing GNSS integrity monitoring systems. A thorough analysis of GNSS-based ETC systems and of GNSS navigation in urban environments is done afterwards with the aim of identifying the most suitable road toll schemes, GNSS receiver configurations and integrity monitoring mechanisms. Receiver autonomous integrity monitoring (RAIM) is chosen among other integrity monitoring systems due to its design flexibility and adaptability to urban environments. A nominal pseudorange measurement model suitable for integrity-driven applications in urban environments has been calculated dividing the total pseudorange error into five independent error sources which can be modelled independently: broadcasted satellite clock corrections and ephemeris errors, ionospheric delay, tropospheric delay, receiver thermal noise (plus interferences) and multipath. In this work the fault model that includes all non-nominal errors consists only of major service failures. Afterwards, the GNSS integrity requirements are derived from the relationship between positioning failures and toll charging errors. Two RAIM algorithms are studied. The first of them is the Weighted Least Squares Residual (WLSR) RAIM, widely used in civil aviation and usually set as the reference against which other RAIM techniques are compared. One of the main challenges of RAIM algorithms in urban environments is the high unavailability rate because of the bad user/satellite geometry. For this reason a new RAIM based on the WLSR is proposed, with the objective of providing a trade-off between the false alarm probability and the RAIM availability in order to maximize the probability that the RAIM declares valid a fault-free position. Finally, simulations have been carried out to study the performance of the different RAIM and ETC systems in rural and urban environments. In all cases, the availability obtained with the novel RAIM improve those of the standard WLSR RAIM