A multi-tier PPP-RTK positioning method based on correction-product availability

High-precision Global Navigation Satellite System (GNSS) positioning services must accommodate changes in the correction products available to user terminals. PPP-RTK enhances precise point positioning through service-side correction products, but the user-side positioning capability attainable under different correction-product conditions has received limited attention. Building on established undifferenced and uncombined (UDUC) PPP-RTK models, this study develops a multi-tier PPP-RTK positioning method. The user-side configurations denoted SPP, PPP, PPP-AR, and PPP-RTK are organized according to the service-side correction products applied at the user terminal. An end-to-end real-time system was implemented, comprising a PPP-RTK service-side platform and an embedded GNSS positioning device. Real-time experiments characterized the accuracy and convergence behavior of each tier. The PPP-RTK tier achieved 0.72 cm horizontal and 1.78 cm three-dimensional RMS accuracy, with a mean convergence time of 7.08 s. The PPP-AR and PPP tiers converged in 4.27 and 15.98 min, respectively, and provided centimeter- and decimeter-level accuracy, whereas the SPP tier provided meter-level accuracy. Following 40 forced hot restarts, fixed PPP-RTK solutions were re-established in 4.53 s on average. These results support the feasibility of an availability-aware multi-tier GNSS PPP service architecture and inform continuity-oriented GNSS positioning-service design in near-Earth PNT applications.