Interoperability Evaluation of Multiple GNSS Systems
Simultaneous use of pseudorange, phase and Doppler data from multiple GNSSs for Position, Velocity and Timing (PVT) requires the alignment of the time and frequency scales of the used GNSSs, and additional calibrations, some of them related to the different signal offsets. The accuracy of the PVT solution is also dependent on the GNSS constellation. However, a comparative analysis seems to be lacking, particularly for the joint use of global and regional constellations. The aim of this work is to study the interoperability of GNSSs and their performances (in particular for Galileo), concerning position, velocity and time. To do this, pseudorange and Doppler data from GPS, GLONASS, Galileo, BeiDou, QZSS, NAVIC and GAGAN recorded of a three-month period (July to September 2025) by ten permanent stations at different geographical locations are processed. We first investigate the alignment of the GNSSs time scales relative to GPS and show that the time scales have different relative offsets of up to several tens of nanoseconds, depending on the GNSS and on the receiver type. Then, the alignment in velocity and frequency is evaluated using Doppler data, and it is found out it is within fractions of cm/sec.