Impact of Real‐Time Ionospheric Determination on Improving Precise Navigation with GALILEO and Next‐Generation GPS

Ionospheric differential refraction at distances of tens of kilometers or more is one of the main problems affecting the capability of instantaneous carrier‐phase ambiguity resolution. As a consequence, the ionosphere affects the feasibility of centimeter‐accuracy navigation with dual‐frequency global navigation satellite systems (GNSSs), such as present‐day GPS, as well as future systems with three frequencies, such as GALILEO and modernized GPS. We have shown in previous work that a real‐time tomographic model of the ionosphere, computed from GPS reference network data, is accurate enough to allow GPS real‐time carrier‐phase ambiguity resolution for a rover at hundreds of kilometers from the nearest reference site. In this work, we study the extension of such techniques to the improvement of instantaneous three‐carrier‐phase ambiguity resolution algorithms, such as three‐carrier ambiguity resolution (TCAR), at medium and long distances (from tens to hundreds of kilometers) and with a minimum of geodetic computation. The datasets used were generated with a modified GNSS satellite signal generator. In particular, the success rate of instantaneous ambiguity resolution with three frequencies can be improved from about 60 percent of all attempts in previous work to about 100 percent with the proposed technique at distances of about 60 km and with low ionospheric values, and to more than 90 percent at distances of more than 100 km under solar maximum conditions.