Integrity Real-time Performance of the Trimble RTX Correction Service

The Trimble RTX correction service provides nowadays one of the best on the market PPP augmentation services in terms of accuracy and fast convergence time. As of March 2019, the corrections will also include the integrity functionality required for safety-critical and autonomous applications. The integrity monitoring system has been developed over the last years and it is now being released and becoming operational. The Trimble RTX technology is based on the estimation of precise satellite orbits, satellite clocks, satellite biases and ionosphere models computed from the data of a worldwide network of GNSS reference stations. This correction data is transmitted to the user via L-band signals from geostationary satellites or the internet. Using dual-frequency or triple-frequency pseudorange and carrier phase observations together with the received correction data, the user receiver can perform absolute cm-level accurate positioning anywhere on the Earth. The system supports all current GNSS: GPS, GLONASS, QZSS, BeiDou and Galileo. An accuracy of 2.5 cm (95%) is achieved after a convergence time of less than 15 minutes (95% of the time) by using a global ionosphere model or less than 1 minute by using regional ionospheric and tropospheric models. The corrections which integrity is checked are the satellite orbits, satellite clocks and the regional atmosphere models for Europe and North America. The integrity checks are done by using the phase observation residuals (after integer ambiguity fixing) of independent monitoring stations and the checks consist of two steps: a Pre-Broadcast step, where potentially faulty corrections are detected and filtered out before leaving the computing server, and a Post-Broadcast step, where additional errors in the transmission channel are caught and alarms are issued to the users. In this paper, the current real-time performance of the Trimble RTX integrity is evaluated, including the accuracy of the corrections and their probability of failure, as well as the probability that the system does not provide alarms within the specified time to alarm.