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Introduction

Nowadays there are many positioning systems, owned and managed by different nations / government. In particular, the main GNSS are:

  • GPS (Global Navigation Satellite System) – USA
  • GLONASS – Russia
  • GALILEO – European Union
  • BeiDou – China
  • QZSS (Quasi-Zenith Satellite System) – Japan
  • IRNSS (Indian Regional Navigation Satellite System) – India

GNSS constellations

Components of a satellite positioning system

A satellite position system is generally composed by the space segment, the control segment, and the user segment.

Space segment

It is constituted by the satellites orbiting around the Earth, usually guaranteeing an almost global ground coverage. Therefore, the visibility of a minimum number of satellites is possible almost everywhere. The main satellite tasks are:

  • Transmit their positions (ephemeris) as well as the signal required to user segment for navigation / positioning applications,
  • Receive and store information from control segment,
  • Correct the orbits by on-board rockets, which managed by control segment.

Space segment

Control segment

It is composed by the ground stations used to control and manage the entire satellite constellation. Main tasks of the control segment are:

  • Tracking the satellites of the space segment
  • Determination, prediction, and distribution of satellite ephemeris.

Control segment

User segment

It is composed by the users that would know their position on the Earth. They need a receiver and an antenna. There are many «level» of instruments, depending on the quality of the on-board electronics:

Geodetic type receivers:

  • for monitoring / long static survey purposes

geodetic_receiver_1

  • for real time applications

geodetic_receiver_2

Low-cost receivers:

  • with the possibility of accessing to raw-data

low_cost_receiver_1

  • Embedded in other devices:

low_cost_receiver_2