Characteristics of inter-frequency clock bias for Block IIF satellites and its effect on triple-frequency GPS precise point positioning

The latest generation of GPS satellites, termed Block IIF, provides a new L5 signal. Multi-frequency signals open new prospects for precise positioning and fast ambiguity resolution and have become the trend in Global Navigation Satellite System (GNSS) development. However, a new type of inter-frequency clock bias (IFCB), i.e., the difference between the current clock products computed with L1/L2 and the satellite clocks computed with L1/L5, was noticed. Consequently, the L1/L2 clock products cannot be used for L1/L5 precise point positioning (PPP). In order to solve this issue, the IFCB should be estimated with a high accuracy. Datasets collected at 129 globally distributed Multi-GNSS Experiment (MGEX) stations from 2015 are employed to investigate the IFCB. The results indicate that the IFCB is satellite dependent and varies with the relative sun-spacecraft-earth geometry. Other factors, however, may also contribute to the IFCB variations according to the harmonic analysis of the single-day IFCB time series. In addition, the results show that the IFCB exhibits periodic signal with a notable period of 43,080 s and the peak-to-peak amplitude is 0.023-0.269 m. After considering a time lag of 240 s, the average cross-correlation coefficient between the IFCB series of two consecutive days is 0.943, and the prediction accuracy of IFCB is 0.006 m. A triple-frequency PPP model that takes the IFCB into account is proposed. When using 3-h datasets, the positioning accuracy of triple-frequency PPP can be improved by 19, 13 and 21 % compared with the L1/L2-based PPP in the east, north and up directions, respectively.