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About this book

This book proposes a general methodology to introduce Global Navigation Satellite System (GNSS) integrity, starting from a rigorous mathematical description of the problem. It highlights the major issues that designers need to resolve during the development of GNSS-based systems requiring a certain level of confidence on the position estimates. Although it follows a general approach, the final chapters focus on the application of GNSS integrity to rail transportation, as an example. By describing the main requirements in the context of train position function, one of which is the safe function of any train control system, it shows the critical issues associated with the concept of safe position integrity. In particular, one case study clarifies the key differences between the avionic domain and the railway domain related to the application of GNSS technologies, and identifies a number of railway-signaling hazards linked with the use of such technology. Furthermore, it describes various railway-signaling techniques to mitigate such hazards to prepare readers for the future evolution of train control systems, also based on the GNSS technology. This unique book offers a valuable reference guide for engineers and researchers in the fields of satellite navigation and rail transportation.

Table of Contents

Frontmatter

Chapter 1. Introduction and Book Objectives

Abstract
Positioning and navigation systems for applications with SoL features require the development of solutions that can ensure the integrity of the provided position information. The concept of integrity must be conjugated together with the concepts of continuity, accuracy and availability. This chapter is intended to briefly introduce these concepts, which will be dealt with more details in the following chapters. The chapter also outlines the main accuracy requirements of railway signalling systems, and the needs of innovative cost-effective railway signalling solutions and anticipates the peculiarities of the railway environment, with respect to the well-known aviation environment. Finally, this chapter summarizes the objectives of the book.
Letizia Lo Presti, Salvatore Sabina

GNSS Integrity

Frontmatter

Chapter 2. Review of Common Navigation Algorithms and Measurements Errors

Abstract
This chapter reports fundamentals of the methods of the position computation based on global navigation satellite systems. In particular, it addresses the method of position computation based on the least square method and describes the errors which affect this type of position estimate.
Letizia Lo Presti, Marco Pini

Chapter 3. Fundamentals of Integrity Monitoring

Abstract
This chapter describes the methods of integrity monitoring, necessary to verify if all the satellites involved in the PVT computation are healthy or not. In particular, we will see the solution adopted by a stand-alone receiver equipped with a system able to check if the hypothesis of nominal conditions (i.e. when all the satellites are healthy) can be considered valid. This is a fundamental step before evaluating the confidence interval associated to the estimated position. The reason why integrity monitoring is a necessary step for the evaluation of the confidence interval is briefly described in Sect. 3.1, while the remainder of the chapter is devoted to the methods of fault detection (FD), and fault detection and exclusion (FDE), generally implemented in the algorithms of receiver autonomous integrity monitoring (RAIM) systems.
Letizia Lo Presti, Giulio Franzese

Chapter 4. Evaluation of the Confidence Intervals

Abstract
This chapter describes the methods of evaluation of the confidence interval of the estimated position (the PL), taking into account the remaining errors, which may be present in the measured pseudoranges, after the application of the FD and FDE algorithms. We have seen in the previous chapter that these algorithms are able to exclude undesired situations. The position is generally considered unavailable if the FD detects unacceptable faults, and then in this case it is not necessary to evaluate the confidence interval, since there is not an estimated position. If the faulty satellites are excluded by the FDE algorithm, the position is accepted, and the confidence interval has to be evaluated. However undetectable errors still remain in the estimated position and they have to be taken into account in the PL computation.
Letizia Lo Presti, Giulio Franzese

Chapter 5. Methods for Protection-Level Evaluation with Augmented Data

Abstract
This chapter describes how an augmentation system can support a GNSS receiver of a vehicle (more in general a mobile object) in the PL evaluation. Since this approach has been firstly adopted in aviation, and it is already operative in some airports, we will describe a generic LAAS architecture, as a typical example of a GBAS, tailored to improve the performance of a GNSS receiver in terms of accuracy and integrity. The major components and features of LAAS will be detailed.
Letizia Lo Presti, Marco Pini

The Railway Application

Frontmatter

Chapter 6. The Rail Environment: A Challenge for GNSS

Abstract
This chapter describes the foundations and principles of railway signalling systems and their main key elements and provides an accurate description of the main European Rail Traffic Management System (ERTMS) properties that can be affected by the introduction of the GNSS technology. In order to bring the readers to understand the complexity of the railway environment and the main differences with respect to civil aviation and maritime environments, Sects. 6.3.1 and 6.3.2 provide an overview of the applicable European Commission Regulations and of the complete Control-Command and Signalling System suitable for obtaining the Single European Railway Area, Sects. 6.3.3 and 6.3.4 outline the reference ERTMS System Architecture with emphasis on the interfaces and the functions to guarantee the interoperability requirements, and Sects. 6.3.5 and 6.3.6 accurately describe the ERTMS dependability requirements such as safety, reliability and availability along with the related reference Mission Profile. Furthermore, Sect. 6.4 describes the current process for assessing the conformity of a single ERTMS constituent and for verifying the ERTMS Command and Control and Signalling Subsystems. Finally, Sect. 6.6 provides a quick description of the on-board train environment with respect to radio frequency interferences, multipath and non-line-of-sight conditions to outline how these phenomena, considered negligible in the civil aviation environment, have a critical role in the railway environment.
Salvatore Sabina, Fabio Poli, Nazelie Kassabian

Chapter 7. A New Perspective for GNSS Based Safe Train Position

Abstract
This chapter describes the virtual balise concept and summarizes the benefits associated with its use in the evolution of the ERTMS system. A possible-enhanced ERTMS functional architecture suitable for implementing the virtual balise concept is also presented along with the detailed description of the main new functional blocks. This chapter also introduces the proposed extensions of the key ERTMS concepts for estimating the train position based on virtual balises, and consequently, an innovative railway integrity concept is described based on the peculiarities of the railway operational rules and the signalling principles for guaranteeing safe train movements. Finally, a preliminary apportionment of the ETCS Core Hazard tolerable hazard rate based on the use of not only physical balises but also virtual balises is presented.
Salvatore Sabina, Nazelie Kassabian, Fabio Poli

Backmatter

Additional information