Objectives Using the real GNSS(global navigation satellite system)observation data, the accuracy and performance of velocity determination at each GNSS frequency point and multi-GNSS are tested and evaluated.
Methods Based on the method of time differenced carrier phase, the mathematical model of multi-GNSS velocity estimation is introduced and the error sources are analyzed.
Results The results show that the accuracy of velocity determination at different frequency is different, the velocity estimation at B1I, B1C, B3I frequency points in BDS(BeiDou navigation satellite system)and E1, E5a, E6, E5b, E5 frequency points in Galileo have the same precision, with the horizontal direction better than 1.5 mm/s and the vertical direction better than 3 mm/s; the velocity estimation accuracy at B2I frequency in BDS is the same as that at L1, L2 and L5 frequency points in GPS with the horizontal accuracy of 1.5-2 mm/s and the vertical accuracy of 3-4 mm/s; the velocity estimation accuracy at G1 and G2 frequency in GLONASS is the worst, with 3-4 mm/s in horizontal direction and 5-5.5 mm/s in vertical direction. The accuracy of double frequency ionospheric free combination is lower than that of single frequency due to the amplification of the observation noise. In addition, the combination of multiple GNSS increases the number of visible satellites, reduces the PDOP(position dilution of precision)value, and can significantly improve the velocity measurement accuracy.
Conclusions Compared with the single GPS system, the accuracy of GPS/BDS/GLONASS/Galileo velocity estimation is improved by 40% in horizontal direction and 46% in vertical direction. At 40° elevation cutoff, the availability rate is improved from 48% to 98% under the condition of the horizontal velocity better than 1 cm/s and the vertical direction better than 2 cm/s.