TABLE OF CONTENTS Chapter 3 delineated the many interesting and effective features of the best testimonial of the navigation world: GPS. Nonetheless, stand-alone GPS cannot be used for applications, like civil aviation, where security is a critical task. This is due to both the nonadequate continuity of the location data, for instance during the precision approach and instrumental landing phases, and the lack of real-time information to the user about the provided quality of service ( integrity). The same applies to the GLONASS system.
An interesting report of a few years ago [1] investigated the ability of GPS to meet the required navigation performance in terms of accuracy, integrity, continuity, and availability, in the frame of the transition, planned by the Federal Aviation Administration (FAA), from a ground-based navigation and landing system to a satellite-based approach exploiting GPS signals. A variety of risks for GPS performance were evaluated, related to multipath, ionosphere and troposphere, satellite ephemeris, unscheduled satellite failures, satellite unavailability due to scheduled maintenance, repair, repositioning or testing, and loss of ground support functions (i.e., health of the operational and master control stations and their associated communications functions) [2 7]. Signal emissions from other normal and expected transmissions were also evaluated in terms of potential interference with GPS signal reception, together with intentional interference sources. Ionosphere and interference risks were found to be the most significant ones. Among unintentional interference sources, commercial VHF radio, over-the-horizon military radars, and broadcast television have been mainly considered, together with sources of intentional interference...
