Exploring the Timing Performance of a Geodetic GNSS Receiver in GPS-Only Mode

Abstract

GNSS receivers provide direct and easy access to the UTC through its hardware 1PPS output. Despite the widespread use of geodetic GNSS receivers, more studies are needed on their timing performance. A campaign mode exercise was conducted with a geodetic GNSS receiver in GPS-only mode to address this gap. The experiment was performed in two modes- without and with an external standard frequency fed to the receiver to study its impact on the performance. The impact of a stable oscillator has been observed by the appreciable improvement in frequency stability of the GNSS time with respect to UTC(NLPI). Though notable improvement in standard deviation is observed with the external reference frequency, the performance in the other mode was within a limit of 10 ns; such results are not reported earlier. Further, this paper proposes a novel method of evaluating the delay of the hardware 1PPS during its derivation from the internal time solution from the measured pseudo ranges. The delay is 30.6 ns for this receiver, though depending on its internal circuit arrangement, it may vary across receivers. Understanding this delay would be crucial for specific timing applications. The importance of finding the delay is explained through a notional application.