Session P2b: Present and Future Space Clocks for Space Applications

Evaluating the Allan Variance in the Presence of On-Orbit GPS III Phase Steps Modeled by a Compound Poisson Process
Travis Driskell, L3Harris Technologies
Location: Seaview A/B
Date/Time: Wednesday, Jan. 29, 10:40 a.m.

Picosecond-level phase disturbances in Global Positioning System (GPS) Space Vehicles (SV) can contribute to the pseudo-range error and be visible to GPS receivers utilizing carrier phase tracking for high precision applications . Such levels of phase steps are observed in the publicly available GPS clock solution products provided by the National Geospatial-Intelligence Agency (NGA) and the International GNSS Service (IGS). In this paper, we evaluate the Allan variance in the presence of picosecond-level phase steps as modeled by a compound Poisson process that uses the step statistics computed from the IGS phase data. First, we will introduce the phase steps observed in the NGA and IGS phase data, correlate the steps to establish the presence of phase steps in GPS III SVs, and compute statistics including mean step amplitude, step variance, and average steps per day to characterize the steps. Next, we will use a compound Poisson process with the step statistics to simulate SV carrier phase with phase steps and verify the simulation with the performance measured in the IGS phase data. Finally, we will evaluate the impact of phase steps on the Allan variance by comparing the results of simulated carrier phase with and without phase steps.
Kerkhoff, Aaron, York, Johnathan, Nelsen, Scotland, Caldwell, Otto, Munton, David, Garcia, Thomas, Bratton, Michael, "A New System for the Detection and Monitoring of Carrier Phase Anomalies in the GPS Constellation," Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014), Tampa, Florida, September 2014, pp. 3542-3553.