Effects of the Relative Dynamics of Ionospheric Irregularities and GPS Satellites on Receiver Tracking Loop Performance

Transionospheric satellite signals are exposed to perturbation, caused by irregularities generated in the ionosphere. However, the characteristics of the satellite motion can have an additional impact on signal perturbation, in addition to the effects of irregularity structures, that drift from west to east during geomagnetic quiet conditions. This paper reports the effect of Global Positioning System satellite geometry, on tracking loop performance of ground-based receivers, during occurrence of ionospheric scintillations. Observations are made from station Calcutta (22.58 degrees N, 88.38 degrees E geographic; magnetic dip 34.54 degrees), located near the northern crest of Equatorial Ionization Anomaly, during three different solar activity periods (March 2014, March 2015, and March 2022). Efforts have been made to study the correlation of east-west component of satellite velocity at Ionospheric Pierce Point (IPP) with duration of loss-of-lock and rate of signal fading (<-10 dB), from ground scintillation pattern observations. Results of this study show 75%-78% correlation between duration of loss-of-lock and eastward component of satellite velocity, for all three period of observation. Subsequently, shorter duration of loss-of-lock has been observed corresponding to satellite velocity being westward. Signal fading rate is found to decrease with increasing satellite velocity, having median value of the fading rate cumulative distribution percentage, corresponding to satellite velocity of 16.69, 31.76, and 19.14 m/s respectively during March 2014, March 2015, and March 2022. Results of this study also indicate direction and component of satellite velocity at IPP to be a dominant cause of signal outage, even during periods of weak to moderate scintillations.