A consistent and grid-based regional slant ionospheric model with an increasing number of satellite corrections for PPP-RTK

Ionospheric corrections are critical in fast precise point positioning real-time kinematic (PPP-RTK), in which the regional slant ionospheric model (RSIM) is commonly used. For the conventional RSIM, only common satellites tracked by the whole set of reference stations are selected in delivering the network corrections to keep the receiver-related biases consistent. This decreases the number of available satellites. Therefore, two kinds of aligned RSIMs are proposed by recovering ionospheric observables and aligning ionospheric observables with the same pivot receiver-related bias. The proposed methods derive a consistent ionospheric model with more satellites involved. Effective strategies to transfer receiver-related biases are investigated, where satellites with a high elevation and many ambiguity-fixed epochs show better performance. To validate the performance of the proposed method, both static and kinematic positioning tests are carried out. For the static test, the aligned RSIM achieved faster convergence than the conventional RSIM, and the positioning accuracy in the east, north, and vertical after the first 1 min is 0.029, 0.026, and 0.074 m, respectively. For the kinematic test, the root mean square (RMS) of positioning errors reduces from 1.00 to 0.65 m for the east, from 0.54 to 0.43 m for the north, and from 0.89 to 0.71 m for the vertical component using the aligned model. Also, two typical urban experiments were carried out, demonstrating a fast convergence within 16 s when the aligned RSIM is added.