All-Frequency PPP-RTK Tightly Coupled With IMU for GNSS-Adverse Areas

The global navigation satellite system (GNSS) network-based real-time kinematic precise point positioning (PPP-RTK) technique, which integrates the advantages of PPP and RTK, has been treasured in the fields, such as the intelligent transportation system, autonomous driving, and so on. However, in complex urban environments, frequent satellite signal obstructions may dismiss observations on a particular frequency for a while, inhibiting the full utilization of satellite observations in conventional single/dual/multifrequency PPP-RTK based on prescribed signal frequencies. The emerging all-frequency PPP-RTK, which provides a plug-and-play framework for any remaining signal frequencies surviving GNSS adverse environments, is better able to address urban scenarios. Nonetheless, satellites with incomplete signal coverage often yield low-quality observations that lead to more severe gross errors in all-frequency PPP-RTK. Fortunately, the inertial navigation system (INS), which strongly complements GNSS, is frequently employed for outlier detection. Therefore, in this study, we developed all-frequency PPP-RTK/INS tightly coupled integration, aiming at fully exploiting the potential of GNSS PPP-RTK in urban areas and robust high-precision positioning. Vehicle-borne experiments conducted in typical urban scenarios were used to evaluate the positioning performance of the proposed system. We found that incomplete frequency coverage observations are more prone to outliers in urban environments, which leads to all-frequency PPP-RTK solutions are worse than the conventional dual-frequency and multifrequency PPP-RTK solutions. After integrating with the INS, all-frequency PPP-RTK/INS can improve 3-D positioning precision by 54% and 46% compared to conventional dual/multifrequency PPP-RTK/INS, achieving 0.12, 0.12, and 0.18 m in east, north, and up components, respectively.