An integrated hierarchical wide-area augmentation for real-time GNSS positioning

Due to the correlation between coordinates, atmospheric delays, and ambiguities, Precise Point Position with Ambiguity Resolution (PPP-AR) needs a long convergence time (around 20 min) to achieve cm-level accuracy. With the help of precise external atmospheric products, PPP-AR convergence time can be reduced to a few minutes or even instantaneously. However, a stable and continuous data transmission in real-time communication could be challenging in more expansive areas due to the massive amount of correction information from dense networks. In addition, data interruptions and switching reference stations also could cause discontinuity or anomalies in the real-time correction information. By combining both wide-area fitting functions and regional un-modeled corrections, we present an integrated hierarchical augmentation method, which could ensure reliable and precise positioning with less communication burden. The first level of the hierarchical model includes the satellite-wise slant ionospheric delay and tropospheric Zenith Wet Delay (ZWD) wide-area fitting models, which provides an essential correction with few model coefficients covering a larger area. Moreover, the residual unmodeled errors and phase residuals can be provided optionally, according to the communication capability and the user’s requirement. The newly developed augmentation mode extends from the current wide-area low-precision to the hierarchical-precision service, which relieves the communication burden and greatly reduces the dependence on the distribution of reference stations. We evaluate our model in the European region, using 103 EUREF Permanent Network (EPN) stations with 200 km station-spacing as modeling stations and 84 stations as external validation. The precision of the wide-area ionospheric and tropospheric delay models are 4.5 cm and 1.3 cm, respectively. With only the wide-area correction information, an convergence time (to 10 cm) of 2 and 3 minutes can be achieved for the horizontal and vertical components, respectively. Based on the magnitude of wide-area unmodeled errors, the optional unmodeled correction broadcast volume can be saved by 40-50% with respect to the legacy interpolation mode. Moreover, instantaneous ambiguity fixing within one to two epochs (1 min) can be achieved if the unmodeled residuals are exploited. Therefore, the proposed hierarchical augmentation mode satisfies different positioning demands of wide-area with low resource utilization.