Comparison of GPS Frequency-Transfer Performance between JPL’s GIPSY PPP and BIPM’s IPPP
Daphna G. Enzer and David W. Murphy, Jet Propulsion Laboratory, California Institute of Technology
Location: Beacon A
GPS can be used an effective tool for comparing frequencies across large distances to better than 1E-16 . At the Jet Propulsion Laboratory (JPL) we process GPS receiver data using GIPSY-OASIS (GPS-Inferred Positioning System and Orbit Analysis Simulation Software) which uses wide-lane phase bias ambiguity resolution  as part of its PPP (Precise Pointing Positioning) algorithm. To process GPS data for the Deep Space Atomic Clock (DSAC) mission , we further devised an algorithm and software for concatenating daily files and correcting for phase jumps and data gaps . Here we compare the frequency-transfer performance of our GIPSY PPP technique, applied to ground receivers, with the well-proven IPPP technique  used at the International Bureau of Weights and Measures (BIPM). We process 10 months of Germany to United States link data  between two International GNSS Service (IGS) stations, both referenced to stable clocks steered to Universal Coordinated Time (UTC). We then subtract two-way satellite time and frequency transfer (TWSTFT) link data  to remove the long-term clock instability component. These same link data were processed with IPPP and reported on by Petit and Meynadier at last year’s PTTI conference . We compare the two techniques and discuss the viability of using GIPSY PPP instead of IPPP  for transcontinental frequency transfer.
 Gérard Petit, “Sub?10–16 accuracy GNSS frequency transfer with IPPP,” GPS Solutions 25, Article number: 22 (January 2021).
 Willy Bertiger, et al., “Single Receiver Phase Ambiguity Resolution with GPS Data,” Journal of Geodesy 84 (March 2010): pp. 327-337.
 Eric Burt, et al., “Demonstration of a Trapped-Ion Atomic Clock in Space,” Nature 595 (July 2021): pp. 43-47.
 Daphna Enzer, David Murphy and William Diener, “Frequency Comparisons via GPS Carrier-phase: Jump Processing, Temperature Compensation and Zero/Short-baseline Noise-floors,” in Proc. of the 50th Annual PTTI, Reston, VA (January 28-31, 2019): pp. 68-82.
 Gérard Petit, et al., “1 × 10?16 Frequency Transfer by GPS PPP with Integer Ambiguity Resolution,” Metrologia 52, no. 2 (April 2015): pp. 301-309.
 Data from International GNSS Service, Daily 30-second observation data, Greenbelt, MD, USA:NASA Crustal Dynamics Data Information System (CDDIS), Accessed July 23, 2021, Subset obtained: 2019-12-27 to 2020-10-26 at http://cddis.gsfc.nasa.gov/Data_and_Derived_Products/GNSS/daily_gnss_o.html.
 Data used were submitted by laboratories for UTC, and processed by the BIPM.
 Gérard Petit and Frédéric Meynadier, “IPPP Links for UTC: Comparison to Existing Techniques,” in Proc. of the 52nd Annual PTTI, virtual conference (January 25–28, 2021): pp. 71-86.