Inter-frequency clock bias: an efficient real-time self-calibration method through the user terminal without a ground reference network

Abstract Multi-frequency integration can improve the performance of precise point positioning (PPP), but the inter-frequency clock bias (IFCB) makes it impossible to directly apply dual-frequency ionospheric-free (IF) combined satellite clock products to multi-frequency PPP processing. In real-time processing, the IFCB network solutions can be solved through a ground reference network. However, this significantly increases the computing burden at the server and may cause the delay of real-time data streams, ultimately exerting a negative impact on the performance of multi-frequency real-time PPP. To improve the efficiency of data processing, a real-time IFCB self-calibration method only using the observations from the user terminal itself is proposed in this study. With the proposed method, an additional ground reference network is no longer needed. Taking GPS triple-frequency observations for analysis, the results indicate that the trend of IFCB self-calibration estimate series gradually approaches that of IFCB network estimate series over time. After applying IFCB self-calibration real-time estimates, the static positioning accuracy of GPS triple-frequency real-time PPP shows an improvement of 32%, 8%, and 12% in the east, north, and up directions, respectively. The corresponding improvement rates are 26%, 25%, and 23% in kinematic mode in three directions, respectively. In addition, compared with GPS dual-frequency real-time PPP, the convergence time of triple-frequency case is slightly shortened. Although the triple-frequency PPP results with IFCB self-calibration corrections are still worse than those with IFCB network corrections, this method enables real-time acquisition of IFCB estimates only through the user terminal, facilitating more efficient and convenient IFCB correction.