VTEC Estimation Performance of Real-Time PPP with Galileo High Accuracy Service

Precise positioning with Global Navigation Satellite Systems (GNSS) requires a significant amount of effort for deliberate modeling of various effects on transmitted signals. Among these error sources, the ionosphere has a special place with its daily variations of total electron content (TEC), disrupting signals and degrading positioning performance. Some attempts to remove ionospheric effects, such as forming ionosphere-free combinations in Precise Point Positioning (PPP) can cause the amplification of observation noise. Using data-driven Global Ionospheric Maps (GIM) from GNSS analysis centers could be an alternative solution. However, precise GIMs are available after 10-11 days from the observation campaign and are not accessible in real-time. Therefore, the demand for real-time and reliable solutions is a hotspot research field in precise positioning.
Real-time PPP (RT-PPP) with undifferenced and uncombined observables can convert the limitations of the ionosphere into an opportunity to make GNSS a versatile tool that is capable of monitoring the ionosphere and achieving high-accuracy positioning in real time. Our work focuses on the performance of ionospheric delay estimation with RT-PPP, using a newly developed real-time correction service, Galileo High Accuracy Service (Galileo HAS). First, International GNSS Service (IGS) stations from low, mid, and high latitudes for day-of-year 140,141, and 143 were selected for RT-PPP data processing. Next, we performed station-based Vertical TEC (VTEC) modeling and compared the results with GIM from the Centre for Orbit Determination in Europe (CODE). In addition, we processed the data from two receivers co-located on the rooftop of the University of Liège Sart Tilman campus B5a building. Finally, characteristics of the between-receiver single difference of estimated ionospheric delays are presented to assess the precision of slant ionospheric delays.