Objectives  Ambiguity resolution is the key for global navigation satellite system(GNSS) high-accuracy data processing. Different from traditional double-difference ambiguity resolution, the undifferenced ambiguity resolution does not need to construct double-difference ambiguity, which is simpler and more efficient.

  Methods  The undifferenced ambiguity resolution is introduced into the BeiDou-3 satellite navigation system(BDS-3)medium Earth orbit satellite real-time filtered orbit determination, and the influence of undifferenced ambiguity resolution on the convergence speed and accuracy of the real-time filtered orbit is analyzed. With observation data from International GNSS Service global network stations, simulated real-time filtered precise orbit determination experiment is conducted with German Research Centre for Geosciences post-processed precise orbit for accuracy assessment.

  Results  The results indicate that while undifferenced ambiguity resolution has little effect on the convergence, it can effectively improve the orbit tangential/normal accuracy; compared with the ambiguity-float orbit, the accuracy of ambiguity-fixed orbit is improved by 1.0%, 18.5%, 19.5% and the error root mean square reaches 6.0, 7.4, 6.2 cm for the radial, tangential, normal directions respectively. Affected by the tangential, normal direction, the orbit accuracy of China Academy of Space Technology type satellites is better than that of Shanghai Engineering Center for Microsatellites type satellites; considering the correlation between narrow lane ambiguity fixed rate and orbit accuracy, narrow lane fixed rate can be used as one of the important indicators of real-time orbit quality.

  Conclusions  Further improvement of real-time filtered orbit relies on the continuous refinement of BDS-3 data processing models.