Page 7 - 卫星导航2021年第1-2合期

Volume 2, Issue 1-2, July 2021 Research Summary

BDS-3: Real-Time Kinematic
With the completion of the BDS-3 full constellation on June 23, 2020, it is worthwhile to
comprehensively evaluate the RTK positioning performance with the BDS-3 full constellation and
its combination with BDS-2. This contribution first investigated the existence of Differential Inter-
System Biases (DISBs) between the legacy B1I/B3I signals of BDS-3/BDS-2. It is discovered that the
DISBs are in fact about zero for the baselines with the same or different receiver types, which imply
that BDS-3 and BDS-2 are fully interoperable and can be considered as one constellation without
additional DISBs when B1I/B3I signals are used for precise relative positioning. Then the single-epoch
short baseline RTK performance of tightly combined BDS-2 and the newly completed BDS-3 was
preliminarily evaluated through ambiguity resolution success rate, ambiguity dilution of precision,
as well as positioning accuracy in kinematic and static modes using the datasets collected in Wuhan.
Experimental results demonstrated that the current BDS-3 only solutions can deliver comparable
ambiguity resolution performance and much better positioning accuracy with respect to BDS-2 only
solutions. Moreover, the RTK performance was significantly improved with tightly combined BDS-
3/BDS-2, particularly in challenging or harsh conditions. The results could provide references for the
fusion of BDS-2/BDS-3 observations in the future.
Related article: Single-epoch RTK performance assessment of tightly combined BDS-2 and
newly complete BDS-3 (doi: 10.1186/ s43020-021-00038-y)

GNSS: Precise Point Positioning
The Fractional Cycle Bias (FCB) product is crucial for the Ambiguity Resolution (AR) in Precise
Point Positioning (PPP). Different from the traditional method using the ionospheric-free ambiguity
which is formed by the Wide Lane (WL) and Narrow Lane (NL) combinations, the uncombined
PPP model is flexible and effective to generate the FCB products. The authors demonstrated the
FCB estimation based on the multi-GNSS (Global Navigation Satellite System) precise satellite orbit
and clock corrections from the international GNSS Monitoring and Assessment System (iGMAS)
observations using the uncombined PPP model. The details of FCB estimation are described with
the Global Positioning System (GPS), BeiDou Navigation Satellite (Regional) System (BDS-2) and
Galileo Navigation Satellite System (Galileo). For the estimated FCBs, the Root Mean Squares (RMSs)
of the posterior residuals are smaller than 0.1 cycles, which indicates a high consistency for the float
ambiguities. For GPS/BDS-2/Galileo hourly static positioning results, the performance of the PPP AR
with the three-system observations is improved by 42.6%, but only 13.1% for kinematic positioning
results. Results indicate that precise and reliable positioning can be achieved with the PPP AR of GPS/
BDS-2/Galileo, supported by multi-GNSS satellite orbit, clock, and FCB products based on iGMAS.
Related article: Estimation of fractional cycle bias for GPS/ BDS-2/ Galileo based
on international GNSS monitoring and assessment system observations using the
uncombined PPP model (doi: 10.1186/ s43020-021-00039-x)