Satellite antenna phase center errors: magnified threat to multi-frequency PPP ambiguity resolution

The dearth of frequency-specific satellite antenna phase centers (APCs), such as GPS Block IIF L5 phase center offsets (PCOs) and BeiDou System (BDS) phase variations (PVs), inconveniences multi-frequency precise point positioning (PPP). We find that the GNSS observation biases caused by incorrect frequency-specific APCs are both spatially incoherent and time variable. This spatiotemporal incoherency will be magnified by over a hundred times in the case of multi-frequency PPP wide-lane ambiguity resolution (PPP-WAR) and is likely to defer PPP convergences. We hence first impose deliberate errors on the Galileo frequency-specific APCs to mimic the common faulty operations of equating the GPS L5 with the L1/L2 ionosphere-free PCOs and ignoring the BDS PVs in typical high-precision GNSS. We then investigate how such APC errors can harm multi-frequency PPP using one month of E1/E5a/E5b data from 43 globally distributed stations. Although the APC errors tested in this study have minimal impact on dual-frequency PPP, a 5-mm horizontal PCO error does prolong multi-frequency PPP convergences by 15%; a 200-mm vertical PCO error or a PV error of up to 10 mm can even grow the convergence times by 60%. The vertical positioning precision of single-epoch PPP-WAR is deteriorated on average by 15 cm under a 200-mm vertical PCO error. Therefore, accurate frequency-specific GPS/BDS satellite APCs should be determined for multi-frequency PPP to maximize its convergence advantages over dual-frequency PPP.