Virtual Reference Station (VRS) Coordinate’s Pattern of QianXun Ground-Based Augmentation System

Abstract

Since May 2016, QianXun Spatial Intelligence Inc. has launched its Beidou ground-based augmentation system (QX-GBAS) which supports high-precision GNSS positioning service within the national coverage. The user first sends its approximate coordinates to QX-GBAS in the NMEA $GPGGA format and subsequently receives 3D Cartesian coordinates of virtual reference station (VRS) and corresponding GNSS code/phase observations encoded in the format of RTCM. Unlike some operational province- and city-level GBASs whose VRS coordinates received by the user equal to those NMEA $GPGGA coordinates sent by the user, QX-GBAS does not always return VRS coordinate exactly equal to the user-sent NMEA $GPGGA coordinates. This study then investigated the pattern of QX-GBAS VRS coordinates in the RTCM message type 1005 and 1006, respectively. Numerical results showed that (1) the QX-GBAS RTCM1006 coordinates were equal to the user-sent NMEA $GPGGA coordinates within the range of 0.9 m (0.03″); (2) the QX-GBAS RTCM1005 coordinates were different from the user NMEA $GPGGA coordinates, but followed a 3′ × 3′ (latitude/longitude) grid pattern. The outcome of this study can be beneficial for both QX-GBAS, or other GBASs, server and users by providing more operational flexibilities and also, protect the homeland security from possible threats.