Rapid Precise Time and Frequency Transfer Using GPS and Galileo Multi-Frequency Precise Point Positioning with Ambiguity Resolution

Precise Point Positioning (PPP) has become a versatile and competitive technique for time and frequency transfer across various fields. However, PPP's long convergence time, caused by slow satellite geometry changes and low pseudorange accuracy, limits its use in real-time time and frequency transfer. This study investigates the impact of GPS and Galileo multi-frequency PPP ambiguity resolution (PPPAR) on time and frequency transfer stability and convergence. We established four time links and evaluated six system and frequency combinations. The results show that multiconstellation and multi-frequency approaches significantly improve short-term stability. They reduce the standard deviation of epoch differences by 10% to 25%. The modified Allan deviation (MDEV) results indicate that multiconstellation and multi-frequency approaches enhance frequency stability by 15 % to 30 % over a 90 s averaging period. While long-term stability remains influenced by satellite clock offsets and environmental factors, multi-constellation and multi-frequency PPP-AR proved to be a robust solution for rapid convergence and enhanced short-time stability, making it particularly suitable for real-time applications.