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The BDS-3 has been officially commissioned since July 31, 2020. As one of the seven services of BDS-3, precision point positioning is free to users in China and its surrounding areas. In order to assess the performance of BDS-3 PPP service, the observation data from eight domestic stations were analyzed in terms of the accuracy of corrections, the coverage of service, the positioning accuracy, and the convergence time. The coverage of service was assessed based on the combination of the number of effectively corrected satellites and the DOP values, and the convergence time was calculated using a slide-and-restart method. The results prove that: 1) The averages of signal in space ranging error (SISRE) (RMS) are 0.10 m and 0.14 m for BDS-3 and GPS respectively. 2) The availabilities of PPP service of BDS-3 only and BDS-3&GPS dual system are both higher than 90% in China and its surrounding areas. 3) The average convergence time of the kinematic PPP of BDS-3 is 17 min (0.3 m horizontally and 0.6 m vertically). After convergence, the average accuracy (95% confidence level) reaches 0.17 m horizontally and 0.26 m vertically. The average convergence time of the kinematic PPP of BDS-3&GPS dual system is 10 min (0.2 m horizontally and 0.4 m vertically). After convergence, the average accuracy (95% confidence level) reaches 0.11 m horizontally and 0.22 m vertically.

BDS-3 has been providing initial service from December 2018. BDS entered the stage of simultaneous service with 2 generations of satellites: BDS-2 and BDS-3. There are three different orbit for BDS satellites including GEO, IGSO and MEO, and 4 open service signals including B1I, B2I, B3I, B1C and B2a. Compared with BDS-2, the on-board payload of the BDS-3 has been redesigned, and the parameters of signals are designed to be better, especially in multipath mitigation. In order to verify the performance of BDS-3 signals in terms of multipath errors, we use data from the “international GNSS Monitoring and Assessment System (iGMAS)” multi-GNSS observation stations to analyze the multipath errors of BDS-2 and BDS-3. The results show that the pseudorange multipath error of BDS-2 has a systematic bias that varies with the elevation angle, and the performance of B3I signals is better than B1I for BDS-2 satellites. While B1I, B3I, B1C, and B2a signals of BDS-3 satellites have pseudorange multipath errors with zero mean characteristic, and BDS-3 B1I, B3I signals multipath error is significantly better than BDS-2. The B3I and B2a signals have better performance than B1I and B1C for BDS-3 satellites.

Signal power level of GNSS satellites is key parameter for service performance. The relationship between navigation signal power and carrier-to-noise ratio (CNR) of GNSS receiver is described. The time variation characteristics of CNR for one station and satellite pair during 10 days and also characteristics between different stations is analyzed. Results show that the relationship between CNR and elevation angle is consistent and repeatable for a specified signal of one station and satellite pair during that 10 days. Then a model related CNR with elevation angle is established based on global observation data. Using the model, CNR changing trend could be predicted, and so its anomaly could be monitored. For more efficient monitoring, we use a mapping method to transform the CNR at different elevation angles to its corresponding value of 90-degree elevation angle. Finally, data from global tracking network are used to validate the feasibility and reliability of this approach. The results show that there are signal power changes for GPS satellites occurred during April 13th 2018 UTC.

Utilization of frequency-division multiple access (FDMA) leads to GLONASS pseudorange and carrier phase observations suffering from variable levels inter-frequency bias (IFB). The bias related with carrier phase can be absorbed by ambiguities. However, the unequal code inter-frequency bias (cIFB) will degrade the accuracy of pseudorange observations, which will affect positioning accuracy and convergence of precise point positioning (PPP) when including GLONASS satellites. Based on observations made on un-differenced (UD) ionospheric-free combinations, GLONASS cIFB parameters are estimated as a constant to achieve GLONASS cIFB real-time self-calibration on a single station. A total of 23 stations, with different manufacturing backgrounds, are used to analyze the characteristics of GLONASS cIFB and its relationship with variable receiver hardware. The results show that there is an obvious common trend in cIFBs estimated using broadcast ephemeris for all of the different manufacturers, and there are unequal GLONASS inter-satellite cIFB that match brand manufacture. In addition, a particularly good consistency is found between self-calibrated receiver-dependent GLONASS cIFB and the IFB products of the German Research Centre for Geosciences (GFZ). Via a comparative experiment, it is also found that the algorithm of cIFB real-time self-calibration not only corrects receiver-dependent cIFB, but can moreover eliminate satellite-dependent cIFB, providing more stable results and further improving global navigation satellite system (GNSS) point positioning accuracy. The root mean square (RMS) improvements of single GLONASS standard point positioning (SPP) reach up to 54.18 and 53.80% in horizontal and vertical direction, respectively. The study’s GLONASS cIFB self-estimation can realize good self-consistency between cIFB and stations, working to further promote convergence efficiency relative to GPS + GLONASS PPP. An average improvement percentage of 19.03% is observed, realizing a near-consistent accuracy with GPS + GLONASS fusion PPP.

We provided the key technologies for BeiDou navigation satellite system (BDS) standard positioning. Using real-time precise point position (RT-PPP) technology to get the precise reference coordinate, the dynamic positioning performance of BDS in service area was evaluated. Our results indicate that the 95% confidence level error is 2.77 and 4.27 m for horizontal and vertical components with B1I signal, 3.24 and 4.95 m for B2I signal, and 4.11 and 6.84 m for B1I and B2I ionosphere-free combination.