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Since its introduction in 2011, Trimble’s RTX positioning service has been providing reliable real-time centimeter-level accurate positioning for standalone GNSS receivers. The service is based on the estimation of precise satellite orbits, clocks and signal biases as well as atmospheric models computed from the data of a worldwide network of GNSS reference stations. The correction data is transmitted to the user receiver via L-band from geostationary satellites or via the internet. Using dual-frequency pseudorange and carrier phase observations together with the received correction data, the user can perform absolute cm-level accurate positioning anywhere on Earth. By using all current GNSS an accuracy of 2.5 cm (95%) is achieved after a convergence time of less than 10 minutes (95% of the time) globally or less than one minute when using regional ionospheric and tropospheric corrections available throughout Europe and North America. In recent years, the service has undergone a major rework introducing new features, such as BeiDou-3 support and integrity monitoring that result in a substantial improvement in terms of positioning performance and reliability. In order to improve the overall positioning performance the Chinese BeiDou-3 system comprising 24 MEO and 3 IGSO satellites was added to the service. With its global coverage and excellent observation quality, BeiDou-3 can be considered an ideal addition to the existing RTX service. In order to support the full set of signals, currently defined by BeiDou-3 ICDs the global RTX tracking network was upgraded to Trimble Alloy receivers and the correction data generation was extended to support the additional frequencies. As a consequence the RTX service is providing correction data for the B1C, B2a, B1I and B3I signals. It will be shown that using all available satellites including BeiDou3 as well as additional signals such as L5, E6 and B3 the convergence time of the RTX global service is very significantly reduced by more than 50 %. For stations with good observation data quality convergence times of less than one minute are achieved without any regional augmentation (RTX-Fast). Since some user groups, especially in the automotive sector, are limited to a subset of satellite systems and signals, the service area of the RTX-Fast correction service was continuously extended over the past years and is now covering complete Europe and the US. Since the RTX-Fast corrections contain very accurate atmospheric corrections derived from a much denser reference station network a user reaches cm-level accuracy in less than one minute even when using only a subset of GNSS. In addition, RTX-Fast corrections are integrity monitored both before broadcast and after reception by dedicated integrity receivers across the service area. In case integrity violations are detected in the broadcast correction data or the integrity monitoring is not available the user receives a corresponding alarm message within seconds. From the very beginning the RTX service allowed to handle switches between redundant RTX server instances and between data centers using a dedicated handover mechanism with minimal user impact. Recently, a new way of server switches was implemented that allows completely seamless switching without impacting clients that can not handle the existing handover mechanism, while maintaining the highest degree of robustness and redundancy. During 10 years of operation Trimble’s RTX correction data service has come a long way and is currently serving more than a hundred thousand users around the world 24/7 with excellent availability. With the upcoming 2021 RTX service release another big step in terms of performance and reliability will become available to the customers. Users with BeiDou-3 capable receivers will see a highly improved performance of the global RTX service in terms of convergence time and robustness. Other RTX users can benefit from much extended RTX-Fast coverage areas including a fully deployed integrity monitoring system. Finally, the impact of maintenance server switches on the RTX data stream and therefore the user application will become virtually invisible. |
