Chapter 2 - Fundamentals of structural and functional organization of GNSS

Abstract

This chapter provides an elementary introduction to the architecture of Global Navigation Satellite System (GNSS). The main purpose of this chapter is to give the user a general idea of the structural and functional organization of GNSS. The structural organization of GNSS constitutes Space Segment (SS)+Control Segment (CS)+User Segment (US). SS consists of a constellation of 24 satellites for Global Positioning System (GPS) and GLONASS and 32 satellites for BeiDou and Galileo that orbit the Earth in circular orbits. Satellites are placed in six or eight orbital planes, with each orbital plane consisting of four satellites and circling the Earth every 12h. The inclination of the orbital planes and the location of the satellites guarantee the visibility of at least six satellites from any place on Earth. GNSS satellites are placed in mid-Earth orbit at an altitude of about 20,000km. To increase redundancy and improve accuracy, the total number of GNSS satellites in the constellation can reach 32 for GPS and GLONASS and 40 for BeiDou and Galileo. CS constitutes stations on Earth that are monitoring and maintaining the GNSS satellites. US supplies receivers that process the navigation signals from the GNSS satellites and calculate position and time.