Simple Methods for the Estimation of the Short-Term Stability of GNSS On-Board Clocks

Jérôme Delporte, Cyrille Boulanger, and Flavien Mercier

Abstract:	The estimation of GNSS on-board clocks behavior is generally a complex task requiring a large ground infrastructure (a global network of ground stations) and an intense computation (the so-called ODTS, Orbit Determination and Time Synchronization). Here, we propose two alternative methods that allow one to easily estimate the short-term stability of GNSS on-board clocks with respect to a given ground station on a pass. In the first method, we simply consider the phase measurements of the RINEX observation files provided by the ground station on which we apply a high-order polynomial fitting. Thus, we keep the high-frequency part of the measurement, which is expected to be representative of the clock difference. In the second method, we carry out a residuals computation on a given pass using precise ephemerides. The ground station phase measurements are considered. We compute the transmission dates and the satellites’ position by interpolation of these dates. Then we compute the theoretical pseudodistance using the satellites’ position and the measurements; the vertical troposphere delay is adjusted. The difference between the measurements and the theoretical pseudo-distance provides an estimation of the clock difference. With these two methods, we can compute the stability of a GNSS on-board clock for each phase observable and for the iono-free phase combination. Obviously, this requires that the stability of the ground station clock is better than the stability of the GNSS on-board clock that we want to estimate. The estimation obtained of the on-board clock has the same sampling rate as the input RINEX phase measurements. For GPS on-board clocks, the results of these two methods using 1 Hz ground stations measurements have been compared to the IGS COD clock products that have a sampling rate of 5 seconds. We obtain a very good agreement up to 1000 seconds. These methods are considered to be simple, fast, and efficient ways to characterize the behavior of GNSS on-board clocks on a given pass.
Published in:	Proceedings of the 42nd Annual Precise Time and Time Interval Systems and Applications Meeting November 15 - 18, 2010 Hyatt Regency Reston Town Center Reston, Virginia
Pages:	215 - 224
Cite this article:	Delporte, Jérôme, Boulanger, Cyrille, Mercier, Flavien, "Simple Methods for the Estimation of the Short-Term Stability of GNSS On-Board Clocks," Proceedings of the 42nd Annual Precise Time and Time Interval Systems and Applications Meeting, Reston, Virginia, November 2010, pp. 215-224.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In