Evaluating the Performance of Low-Cost PPPRTK Using Fugro’s NextG4 Service

Fugro’s long-standing history of providing global GNSS positioning capability has evolved into its NextG4 service, in which real-time corrections are transmitted to mobile users to enable integer ambiguity resolution-based Precise Point Positioning (PPPIAR) based on GPS, GLONASS, Galileo and BeiDou carrier-phase and code observations. Traditionally Fugro’s NextG4 products, that include orbit, clock, uncalibrated phase delay and inter-frequency code bias corrections, are applied by offshore users who operate high-grade receivers. In this contribution we evaluate for the first time the performance of Fugro’s NextG4 corrections when applied to a low-cost u-blox F9P receiver, a multi-GNSS, multi-frequency mass-market receiver that is equipped with a patch antenna. We first compare the IAR and positioning performance of a stationary u-blox F9P in an open-sky environment with a high-grade Septentrio AsteRx-U3 receiver. As a consequence of the low-cost patch antenna used by the u-blox F9P, its code measurement noise is much higher than that of high-grade receivers. This has as effect that the use of NextG4 products only is not sufficient, as it would lead to unacceptably long convergence times, but precise ionospheric corrections are needed as well. For this purpose, we generate PPP-RTK corrections that include ionospheric corrections from a single reference station. Together with the NextG4 corrections these single-station corrections enable PPP-RTK. Applying corrections from a reference receiver at a 7 km distance we show that for the stationary u-blox F9P data the mean time-to-fix ambiguities is 19 s, vs. instantaneous ambiguity resolution for the Septentrio receiver applying the same corrections. The fixed positioning accuracy (root-mean-square; RMS) is at the 2–4-centimeter level for the stationary u-blox F9P. We also demonstrate the performance of NextG4 + PPP-RTK corrections for a dynamic u-blox F9P operating in a suburban environment. Although in such environment there are obstacles resulting in lower availability of PPP-RTK fixed solutions and more wrong fixes, using the u-blox F9P a fixed positioning RMS error of 10 centimeters horizontally and 25 centimeters vertically is feasible.