The upper part of the Earth's atmosphere, which extends from approximately 50 to 2000 km and completely encircles the Earth is called the ionosphere as it is ionized by solar radiation. Electron and ions densities may vary in complex manner with altitude, geographical location, season and time as well as solar and magnetic activity. When the radio frequency (RF) signals, such as Global Navigation Satellite System (GNSS) signals, pass through the ionosphere, they may experience amplitude and phase disturbances along their path from the satellite to the ground base receivers. Those disturbances are usually caused by small scale irregularities in the ionosphere and manifest themselves as amplitude fading and/or the phase variations of the RF signals, a phenomenon called "scintillation". Over several decades GNSS systems have been used to monitor ionospheric influence on the RF signals using all available satellite constellations (the American system - GPS, the Russian system - GLONASS and the new and yet incomplete European system - GALILEO). The increasing number of available satellites facilitates improved investigation of ionospheric threats and reception issues of the RF signals, such as multi-path or interference.

A short introduction of the ionosphere and its threats on RF signals will be given. The influence of ionospheric phenomena on GNSS signals in equatorial region will be presented, using both GPS and GALILEO signals. Its effects will be quantified using two standard scintillation parameters (scintillation indices S4 and SigmaPhi) and variations of the total electron content (TEC).