Unmanned surface vehicles (USVs) are becoming increasingly important for ocean operations and monitoring, but their precise positioning remains challenging. Real-time kinematic (RTK) technology, commonly used for cm-level positioning in cities, is unsuitable for USVs because it requires nearby reference stations. To address this, we present the uncombined precise point positioning ambiguity resolution (UC PPP-AR) solution, where wide-lane (WL) and narrow-lane (NL) uncalibrated phase bias (UPD) products estimated by the ionosphere-free (IF) PPP model are used. To evaluate the performance of the proposed model, we conducted kinematic USV tests. The results show that the proposed model could shorten the convergence time and achieve cm-level positioning accuracy, with horizontal accuracy better than 2 cm and vertical accuracy better than 5 cm, which is better than that of IF PPP-AR. These results demonstrate the feasibility of the UC PPP-AR technique for USV precise positioning. However, IF PPP-AR may be a better choice if computational consumption time (CCT) is a concern.

This study decodes the BDS-3 PPP-B2b binary data broadcast by BDS satellites using a self-developed software decoder, RT-B2b (Real-Time PPP-B2b). The orbit, clock corrections, and differential code biases (DCB)—collectively referred to as State Space Representation (SSR) corrections—are extracted from the decoded messages. Subsequently, precise satellite orbits and clock offsets are recovered in real time by integrating the SSR corrections with the broadcast ephemeris. The characteristics and accuracy of the SSR corrections are first evaluated. The performance of real-time PPP is then assessed through both static and kinematic experimental schemes, with particular emphasis on the kinematic positioning of a marine buoy. The results demonstrate that the developed software decoder can reliably decode the PPP-B2b SSR corrections and derive accurate orbit and clock products. In terms of positioning performance, real-time PPP achieves centimeter-level accuracy of 4–5 cm in static terrestrial scenarios and decimeter-level accuracy of 1–2 dm in the kinematic marine buoy scenario. This study validates the reliability of the PPP-B2b real-time service in marine environments, thereby providing a valuable reference for marine precise positioning and the practical application of high-accuracy positioning information.