Characterization of periodic variations in the GPS satellite clocks

Abstract

Standard Form 298 (Rev. 8-98)Prescribed by ANSI Std. Z39.18Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. The clock products of the International Global Navigation Satellite Systems (GNSS) Service (IGS) are used to characterize the timing performance of the GPS satellites. Using 5-minute and 30-second observational samples and focusing only on the sub-daily regime, approximate power-law stochastic processes are found. The Block IIA Rb and Cs clocks obey predominantly random walk phase (or white frequency) noise processes. The Rb clocks are up to nearly an order of magnitude more stable and show a flicker phase noise component over intervals shorter than about 100 s. Due to the onboard Time Keeping System in the newer Block IIR and IIR-M satellites, their Rb clocks behave in a more complex way: as an apparent random walk phase process up to about 100 s then changing to flicker phase up to a few thousand seconds. Superposed on this random background, periodic signals have been detected in all clock types at four harmonic frequencies, n × (2.0029 ± 0.0005) cycles per day (24 hr UTC), for n =1, 2, 3, and 4. The equivalent fundamental period is 11.9826 ± 0.0030 hours, which surprisingly differs from the reported mean GPS orbital period of 11.9659 ± 0.0007 hours by 60 ± 11 s. We cannot account for this apparent discrepancy but note that a clear relationship between the periodic signals and the orbital dynamics is evidenced for some satellites by modulations of the spectral amplitudes with eclipse season. All four harmonics are much smaller for the IIR and IIR-M satellites than for the older blocks. Awareness of the periodic variations can be used to improve the clock modeling, including for interpolation of tabulated IGS products for higher-rate GPS positioning and for predictions in real-time applications. This is especially true for high-accuracy uses, but could also benefit the standard GPS operational products. The observed stochastic properties of each satellite clock type are used to estimate the growth of interpolation and prediction errors with time interval. REPORT TYPE 1. REPORT DATE (DD-MM-YYYY) TITLE AND SUBTITLE AUTHOR(S) PERFORMING ORGANIZATION REPORT NUMBER PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) SPONSOR / MONITOR'S ACRONYM(S) 9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) SPONSOR / MONITOR'S REPORT NUMBER(S)

Rapid re-convergences to ambiguity-fixed solutions in precise point positioning

“…The satellite FCB jk w B is normally deemed rather stable over at least 24 hours Laurichesse et al 2009) (Senior et al 2008), if a consistent yaw-attitude model is applied to GPS satellites (Kouba 2009). Moreover, GPS satellite orbits are tightly constrained by dynamic force models, and thus the residual orbit errors should change smoothly in theory.…”

“…Third, due to the high correlation between jk t and the satellite orbits (Senior et al 2008), favorable user range errors of centimeter level can be achieved (Hauschild and Montenbruck 2009). Nonetheless, this jk t is normally a predicted value due to the communication delays in real-time applications.…”

“…Nonetheless, this jk t is normally a predicted value due to the communication delays in real-time applications. Fortunately, Senior et al (2008) reported that the Rubidium and Cesium clocks on current GPS satellites can be precisely predicted to a precision of better than 0.1 ns up to a period of 40 s which covers typical communication delays.…”

On the capabilities of the inaction method for extracting the periodic components from GPS clock data

“…The onboard atomic frequency standard (AFS) is a fundamental element of a GNSS satellite, it plays an important role in the determination of the user position and characterizing the timing performance of the GNSS satellites, thus the satellite clock stability directly affects the range measurement and limits the navigation accuracy (Senior et al 2008;Cernigliaro et al 2013a, b;Hauschild et al 2013). Thus, it is meaningful to establish the GNSS clock models with high precision for the GNSS positioning and timing capabilities.…”

“…The IGS published the Broadcast, Ultra-Rapid, Rapid and Final products. Among them, the IGS Final products have the highest quality and internal consistency of all IGS products, which provide an opportunity for detecting the GPS clock characteristic with higher accuracy and finer temporal resolution (Senior et al 2008).…”