A New Strategy for Improving Multi‐Frequency PPP‐RTK Ionospheric Correction Availability and User Performance in Low‐ and Middle‐Latitudes

Abstract

High‐precision regional ionospheric correction products are essential for achieving accurate and fast‐convergence solutions in Precise Point Positioning Real‐Time Kinematic (PPP‐RTK). For users in low‐ and middle‐latitudes, PPP‐RTK server narrow‐lane (NL) ambiguity resolution (AR) typically requires more than 10 min, which largely affects the user performance in this region. Therefore, this study proposes to fix only extra‐wide‐lane (EWL) and wide‐lane (WL) ambiguities in slant total electron content (STEC) correction generation, and then assesses the benefits of multi‐frequency PPP‐RTK on both server and user sides. Results show that STECs derived from EWL + WL ambiguity‐fixed solutions are highly consistent with those from full ambiguity‐fixed (WL + NL) solutions, with standard deviations below 1.2 cm. This confirms that EWL + WL‐fixed measurements can provide reliable STEC corrections for user enhancement. Multi‐frequency measurements improved ambiguity‐fix rates by 32.7% and increased the number of ambiguity‐fixed satellites by 6.6 in the first 0.5 hr for the server algorithm. Performance evaluations of PPP‐RTK across different latitude regions indicate that the incorporation of multi‐frequency observation data effectively overcomes the challenges posed by the active ionosphere at mid‐ and low‐latitudes. This approach significantly shortened convergence times at low‐latitude stations by 49.3%, 45.9%, and 24.6% in the east, north, and up directions, respectively. In mid‐latitude regions, the corresponding reductions were 48.6%, 43.6%, and 18.6%, respectively. Moreover, in cold‐start conditions, five‐frequency measurements achieved rapid convergence within about 4 min horizontally and 8 min vertically, compared to over 6 and 10 min, respectively, for dual‐frequency solutions.