Apparent clock and TGD biases between BDS-2 and BDS-3

Abstract

With the official commencement of the BDS-3 service, the BeiDou navigation satellite system (BDS) has become a global navigation satellite system. The characteristics of the new BDS-3 satellites, including code bias, are worth investigating. An apparent pair of clock and timing group delay (TGD) biases between BDS-2 and BDS-3 are found when assessing the BDS signal-in-space range error (SISRE) with 5-months of data spanning day of year (DOY) 6 to 145 in 2019, which results from the system bias between the broadcast ephemeris and the precise products provided by Wuhan University and the Chinese Academy of Science. The biases of the broadcast ephemeris are therefore calibrated when aligning to precise products. When these biases are corrected, the overall performance of the BDS SISRE decreases from 1.41 to 0.84 m for the B1I/B3I frequency. To further investigate the biases, we analyze 68 multi-GNSS experiment stations equipped with different receivers based on raw pseudorange measurements. It is found that the clock bias seems similar at each receiver, while the TGD bias from B3I to B1I depends on receiver type, with a value of − 0.48, − 0.98, and − 1.60 m for Javad, Trimble, and Septentrio receiver, respectively. The estimated average clock and TGD biases show good agreement with that from broadcast ephemeris and precise product comparison. When the calibrated clock and TGD biases are corrected in the BDS-3 satellites, the SPP performance improves from 0.3 to 31.8%, depending on frequency and receiver type. For real-time kinematic positioning, when the clock and TGD biases are corrected, the ratio value for ambiguity resolution increases and the fixing rate also improves from 59.79 to 74.44% at B1I frequency.