Real-time detection and identification of BDS-3 PPP-B2b signal-in-space anomalies in the user-side

The BeiDou global navigation satellite system (BDS-3) provides precise point positioning (PPP) service through the PPP-B2b signal. Users in China and its surrounding areas can perform real-time PPP to achieve high-precision positioning solutions through this service. Obviously, the quality of PPP-B2b corrections plays an important role in the PPP performance. However, the accuracy degradations in PPP-B2b orbit corrections may occur due to unannounced orbit maneuvers and improper orbit modeling, and the quality of PPP-B2b clock corrections can also be affected by undetected cycle slips, insufficient continuous observation and bad station-satellite geometry due to poorly distributed tracking stations. If these abnormal PPP-B2b corrections are applied, the positioning accuracy would be seriously reduced. Therefore, it is necessary to detect and identify PPP-B2b SIS anomalies in the PPP process. In this paper, we propose a real-time detection and identification method of BDS-3 PPP-B2b SIS anomalies. The proposed method can be implemented in the user-side and it mainly consists of three steps, which includes validity verification of PPP-B2b orbit and clock corrections based on their valid ranges, reasonability examination of the signal-in-space range error of broadcast ephemeris with respect to PPP-B2b ephemeris, and consistency check of PPP-B2b corrections at adjacent epochs. The first step is designed to detect and identify invalid PPP-B2b corrections, while the second step is intended to detect and identify significant PPP-B2b SIS anomalies, and the final step aims to detect and identify relatively small PPP-B2b SIS anomalies. Several experiments involving different types of PPP-B2b SIS anomalies are carried out to validate the proposed method. The results demonstrate that the proposed method can detect and identify PPP-B2b SIS anomalies, thereby enhancing positioning performance.