Characterizing and Modeling the BDS-3 Time Group Delay Error for ARAIM

In the BDS-3 constellation, only the B3I signal is used to compute the broadcast clock offset. However, because advanced receiver autonomous integrity monitoring (ARAIM) uses dual-frequency measurements, the time group delay (TGD) must be considered in BDS-3-based ARAIM applications. The existing BDS-3 error model is therefore not sufficient to describe the actual TGD error encountered by aviation users. Specifically, the estimated signal-in-space error underestimates the actual error, which cannot be bounded by the estimated user range accuracy and nominal bias. This inaccuracy results in a loss of integrity. To avoid this risk, this paper develops a separated Gaussian model to bound the TGD error for BDS-3 in ARAIM. Using a one-year data set, this paper characterizes and bounds the TGD error for different signal combinations. Of the tested combinations, the B1C/B2a signal combination resulted in the smallest standard deviation of 0.78 m and a corresponding bias component of 0.71 m. We suggest that this signal combination be adopted for use in ARAIM.