Enhancing Real-Time Kinematic Time Transfer with PPP using Galileo HAS service Leveraging an Advanced Clock Model

Precise Point Positioning (PPP) is an advanced technique for GNSS-based time transfer, supporting both static and kinematic applications. However, kinematic scenarios pose significant challenges due to environmental sensitivity, which degrades the robustness of clock parameter estimation. Conventional approaches often model receiver clock offsets as white noise, leading to suboptimal performance under dynamic conditions. To address this issue, we propose an advanced clock modeling method for real-time kinematic timing. The model integrates a second-order state transition framework with differential carrier phase-based frequency estimation, aiming to improve clock stability and filtering accuracy. The study is organized into three parts. First, a comparative evaluation of four real-time precise products (CAS, CNES, WHU, and HAS) was conducted across multiple IGS stations to assess their baseline timing performance. Results confirm that HAS demonstrates favorable timing stability, supporting its use in dynamic applications. Second, the conventional model was compared with white noise strategies using simulated kinematic data. The improved model significantly reduced re-convergence effects and improved filtering accuracy, with standard deviation (STD) reductions of 39.63% for CAS and 41.60% for HAS. Third, to validate the advanced model in real-world performance, the model was applied to a field experiment using a moving vehicle and HAS corrections. The results show a 30% improvement in STD and notable enhancements in clock frequency estimation. Modified Allan Deviation (MDEV) analysis further confirmed improved short-term and long-term stability, with short-term fluctuations approaching the 10⁻¹⁴ level. These results demonstrate the feasibility and robustness of the proposed clock model for kinematic GNSS timing applications, particularly when integrated with real-time products like HAS.