The 2024 GPS Accuracy Improvement Initiative

Abstract

Following several performance enhancements, GPS has provided a stable signal-in-space range error (SISRE) of about 50 cm (RMS) for more than a decade. As of early 2024, a major SISRE reduction by about 30% could be noted that helps to maintain the competitiveness of GPS in comparison with the Chinese BeiDou system and reduces the performance difference with respect to the European Galileo system. Based on analyses of onboard clock stability and broadcast navigation messages, the SISRE enhancement can be attributed to a combination of clock switches on selected satellites as well as an overall reduction of the mean time between navigation data uploads. The additional adoption of new transmit antenna phase center offsets in the control segment has no immediate performance impact but affects the comparison of broadcast and precise orbits. Following the aforementioned operational changes, SISRE values for dual-frequency P(Y)-code positioning with the legacy navigation message (LNAV) were found to decrease to roughly 30 cm from March 2024 onward, and marginally worse results are obtained for users of the civil L1/L2 signals and the L2 civil navigation (CNAV) message. Single-frequency LNAV users, on the other hand, experience only a minor benefit, since orbit and clock information improvements are largely masked by the non-availability of group delay information for the L1 C/A signal relative to the L1 P(Y) signal.