## 1 Introduction  
Over the past three decades, the concept of precise absolute positioning has evolved significantly since its initial formulation [1, 2, 3, 4, 5]. Today, the Precise Point Positioning (PPP) method is widely applied across a broad spectrum of scientific and engineering domains [6], including seismology [7], reference frame determination [8], atmospheric sounding [9, 10], natural hazard monitoring [11], and the estimation of drone trajectories [12]. PPP can achieve a millimeter- to centimeter-level accuracy in static, post-processed applications and a decimeter-level accuracy in kinematic and real-time scenarios. However, the primary limitation of PPP remains its relatively long convergence time [13]. In response to this limitation, substantial research efforts in recent years have focused on enhancing the efficiency and reliability of absolute positioning. Notable advancements include the development of PPP with Ambiguity Resolution (PPP-AR) [14, 15], PPP-Real-Time Kinematic (PPP-RTK) [16, 17], different/combined products that are available [18, 19, 20], and the use of multi-GNSS and multi-frequency measurements [21, 22, 23, 24]. In parallel, interest has grown in single-frequency solutions and low-cost GNSS receivers, particularly for emerging technologies like smartwatches, drones, and smartphones [25; 26]. In the coming years, the adoption of PPP is expected to expand further, particularly in real-time applications. This trend is driven by ongoing technological developments, including the increasing use of unmanned aerial systems, the advancement in smart city infrastructures, and the rising demand for reliable, high-precision positioning in autonomous systems. These use cases require independent, globally available, and highly accurate localization solutions. Recent advancements in GNSS infrastructure have further accelerated the evolution of precise positioning techniques. Next-generation satellites--such as the GPS Block III, which enables additional observations on the L5 frequency [27]--are gradually being deployed. Concurrently, the number of operational Galileo satellites continues to increase [28]. As the Galileo constellation expands, further improvements in positioning accuracy are anticipated, particularly when leveraging onboard ephemeris products [29; 30; 31]. Notably, while GPS ephemeris data are updated every two hours, Galileo satellites provide more frequent updates, ranging from every 10 to 60 min. To facilitate high-accuracy positioning in real time, the International GNSS Service (IGS) initiated the Real-Time Pilot Project in 2007 and officially launched the Real-Time Service (RTS) in 2013 [32; 33]. The RTS supports real-time applications by providing access to precise GNSS products, including orbit and clock corrections, as well as code and phase biases [34]. These corrections serve as a viable alternative to ultra-rapid products, thereby enabling global real-time PPP, time synchronization, and natural hazard monitoring. Currently, IGS RTS offers multi-GNSS combination products--SSRA02 IGS1/SSRC02 IGS1, which support GPS, GLONASS, and Galileo, and SSRA03 IGS1/SSRC03 IGS1, which also include BeiDou corrections. These corrections are applied to broadcast data but require an internet connection and compatible software such as the BKG NTRIP Client (BNC) [35]. In addition to the official IGS RTS solutions, several individual Analysis Centers (ACs) provide their own real-time products [36]. A study by [PERSON] et al. [37] comparing official combined RTS corrections and individual AC products showed that the highest accuracy was achieved using corrections from CNES and WHU, with CNES offering superior availability. Despite their utility, the dependence on internet connectivity limits the use of these products in many regions. Recently, new correction services broadcast directly via navigation systems have emerged, offering enhanced accessibility.