Assessment of Multifrequency Precise Point Positioning (PPP) Augmentation System Enhanced With Ionospheric Corrections Based on Real-Time Corrections

Over the past few decades, the Precise Point Positioning (PPP) technique has primarily been employed in post-processing applications due to its flexibility and high precision. However, two critical challenges continue to limit its broader application in dynamic and time-sensitive applications. First, there remains a lack of stable and publicly available multi-GNSS, multi-frequency real-time products, which are essential for enabling rapid integer ambiguity resolution. Second, research on large-scale, high-precision ionospheric modeling remains underdeveloped, causing the rapid convergence of real-time PPP to rely heavily on dense regional reference networks. To overcome these limitations, this study develops a PPP augmentation system that provides multi-GNSS and multi-frequency corrections to support rapid integer ambiguity resolution, which are subsequently uploaded to the IGS caster (products.igs-ip.net). Furthermore, motivated by the demand for accurate ionospheric constraints to enhance convergence across regional and global scales, a modified Adjusted Spherical Harmonic Function (ASHF) model is proposed to generate precise ionospheric corrections under sparse network conditions. Real-time GNSS observations from multiple monitoring stations are simultaneously processed to assess the performance of the proposed methods. Statistical analysis indicates that the average Time-To-First-Fix (TTFF) of PPP-IAR is approximately 50.2 seconds, with an average positioning accuracy of 0.005/0.005/0.022 m in the North/East/Height components. Moreover, the proposed ionospheric model, based on a network with an average baseline of 244.6 km, achieves roughly a 90% improvement in model accuracy compared to the conventional ASHF method. Finally, validation through PPP-RTK experiments demonstrates a 36.9% reduction in average TTFF — from 62.2 seconds (PPP-IAR) to 39.6 seconds (PPP-RTK) — along with a modest improvement in positioning precision, thereby confirming the effectiveness of the proposed approach in addressing the key limitations of real-time PPP.