Estimability analysis of differential inter-system biases and differential inter-frequency biases for dual-frequency GPS and BDS combined RTK

Inter-system biases (ISBs) and inter-frequency biases (IFBs) are critical for the data processing of multi-frequency and multi-constellation global navigation satellite systems (GNSS). Calibration of the ISB and IFB makes it possible to enhance the accuracy, integrity, and availability of multi-GNSS positioning, navigation, and timing. In this study, we investigate the magnitude and stability of the code and carrier phase differential intersystem biases (DISBs) between the GPS/BeiDou navigation satellite system (BDS) L1- B1/L2-B2 and differential inter-frequency biases (DIFBs) between L1-L2/B1- B2 using zero and short baseline data collected using both identical and different receiver types in realtime kinematic (RTK) positioning. We verify that the code and carrier phase DISBs of GPS/BDS L1-B1/L2-B2 and DIFBs of L1-L2/B1-B2 are both approximately constant on the timescale of a consecutive five-day observation period from a statistical perspective, and can thus be corrected by a priori DISB and DIFB, respectively. Moreover, the performance of the a priori model correction and real-time estimation strategies for the DISB and DIFB are compared. Both can precisely correct the DISB and DIFB and achieve significantly improved performance for multi-GNSS inter-system and inter-frequency combined RTK positioning compared to the classical intra-system and intra-frequency combined RTK approach. The DISB and DIFB using the a priori model correction and real-time estimation effectively improve the positioning model strength, thereby enabling superior performance for multi-GNSS positioning.