Research on evaluation of GNSS system broadcast ERP parameters

Modernized navigation messages of Global Navigation Satellite Systems like BDS, GPS, QZSS and IRNSS include earth rotation parameters (ERPs), namely the pole coordinates and UT－UTC (ΔUT1). Broadcast ERPs are primarily needed for space-borne GNSS applications that require transformations between earth-fixed and inertial reference frames like satellite precise orbit determination as well as earth to the moon navigation. Based on the International GNSS Service (IGS), we obtained broadcast ERP data for BDS, GPS, QZSS, and IRNSS from January 1, 2022 to June 5, 2023. Evaluate the discontinuity of broadcast ERP, the results show that for GPS and IRNSS, the discontinuity of polar motion is 0.9 to 1.4 mas, and the ∆UT1 discontinuity is about 0.2 ms. The discontinuity of polar motion is about 0.1 mas, and the ∆UT1 discontinuity is about 0.02 ms for QZSS. The discontinuity of BDS polar motion is about 4.5 mas, and the ∆UT1 discontinuity is about 1.3 ms. Compared with the external reference 14C04 sequence of the International Earth Rotation and Reference System Service (IERS), the QZSS polar motion error is about 0.6 mas, and the ∆UT1 error is about 0.27 ms. The polar motion of GPS and IRNSS is about 2.4 mas. For ∆UT1, the GPS error is about 0.36 ms, the IRNSS is about 10.47 ms, which is a significant difference. BDS polar motion error is about 6 mas, and ∆UT1 error is about 1.2 ms. Due to less frequent update intervals, compared with GPS, BDS performs worse by a factor of 1.5 and 2.5 for polar motion and ∆UT1 error, respectively.