Estimating GPS BLOCK IIF L5 Satellite Antenna Phase Center Offsets for Rapid Triple-frequency PPP Ambiguity Resolution

ION GNSS+ 2021 Student Paper Award winner. The GPS L5 antenna phase center offsets (PCOs) for the BLOCK IIF satellites have been missing over the past decade, while the Galileo and BeiDou satellites’ multi-frequency PCOs have been officially released since the year of 2017. The underlying risks of duplicating the L1/L2 satellite antenna PCOs for the L5 signals, as usually conducted in most literatures for multi-frequency GPS precise point positioning (PPP), are underestimated or even unrealized by the GNSS community. However, recent studies have shown that incorrect third-frequency PCOs can significantly deteriorate the efficiency of multi-frequency PPP ambiguity resolution (PPPAR). Since traditional methods can only address ionosphere-free PCO estimation, we develop an approach to compute the L5 PCOs for the BLOCK IIF satellites using uncombined triple-frequency GPS observations with a second satellite clock estimated on L5 to mitigate time-variable inter-frequency satellite clock biases. One year (2019) of GPS data from about 135 globally distributed stations are used. Our L5 PCO estimates over the year manifest high temporal stability with standard deviations of about 3 mm in the x and y components and about 20 mm in the z component. Of particular note, the differences between the L1/L2 satellite PCOs and our L5 PCO estimates can reach a maximum of 91 mm for the z component. We further used 31 days of GPS data from 21 IGS stations in 2020 to evaluate our L5 PCO estimates. It is shown that the convergence times of triple-frequency PPP-AR in the case of our L5 PCO estimates are shortened on average by 15% compared to those based on the duplication of L1/L2 PCOs for the L5 signals. We also carried out a vehicle-borne GPS experiment where triple-frequency PPP-AR using our L5 PCO estimates achieved 18% faster convergences than those using the L1/L2 PCO duplications for the L5 signals. We demonstrate that it is critical to use accurate satellite antenna PCOs, especially for the third-frequency signals, to maximize the convergence advantages of multi-frequency PPPAR over its dual-frequency counterpart.