Single-Frequency Multi-GNSS PPP-RTK for Smartphone Rapid Centimeter-Level Positioning

The availability of raw Android global navigation satellite system (GNSS) data is driving innovation in high-precision positioning using Android smartphones. However, inconsistent pseudorange and phase observations, low dual-frequency data integrity, and unknown receiver-side hardware biases prevent the ambiguity resolution of GNSS precise point positioning (PPP) for smartphones. In this study, we thus provide a comprehensive real-time kinematic precise point positioning (PPP-RTK) strategy. First, carrier phase observations are adjusted to be consistent with the pseudorange observations. Next, rapid single-frequency PPP convergence is achieved by regional atmospheric enhancement. Finally, intersatellite difference ambiguities are formed to eliminate unknown receiver-side hardware biases and combined with the partial ambiguity resolution strategy to achieve ambiguity-fixed centimeter-level smartphone PPP-RTK positioning. The results show that using the proposed PPP-RTK strategy, the root mean square (rms) of ambiguity-fixed solution positioning errors is 0.7, 1.3, and 2.5 cm in the east, north, and upper components, respectively, for a representative Huawei P40 smartphone connected to an external survey-type antenna, and 1.2, 1.5, and 5.8 cm for the P40 smartphone using its embedded antenna in an open-sky environment. And their ambiguity fixing rates all reached more than 98%. In 21 sets of experiments, PPP-RTK for smartphones with external and embedded antennas took an average of 1.0 and 63.5 s, respectively, to converge to an ambiguity-fixed solution with a horizontal positioning error within 5 cm. This provides a way for rapid and high-precision GNSS positioning in stand-alone mode for smartphones, which may facilitate the development and widespread use of smartphone high-precision GNSS positioning.