ABSTRACT
Global navigation satellite system (GNSS) is a generic reference for any navigation system based on satellites; the system in widespread use today is the United States' global positioning system (GPS). This chapter explains the principles and operation of GNSS and provides a review of emerging augmentation systems used to increase GPS accuracy, availability and integrity for aircraft navigation. GPS receivers are often incorporated into multi-mode receivers (MMR) along with other radio navigation systems. GNSS has various levels of operation depending on how many satellites are in view. Three satellites provide a two-dimensional position fix; four satellites or more are desirable for optimum navigation performance. GNSS constellations require augmentation systems to meet ICAO performance requirements for en route, terminal, approach and landings. Automatic approach and landing with GNSS will use ILS/MLS to mitigate for satellite outage and/ or disruption.
