Abstract
Integer ambiguity resolution enabled precise point positioning, PPP-RTK, which is becoming one of the most popular global navigation satellite system (GNSS) positioning modes. Owing to the presence of rank deficiencies in the system of GNSS observation equations, one needs to choose some of the GNSS parameters as S-basis and let the remaining parameters absorb them. Doing so forms a full-rank PPP-RTK model whose combined parameters are estimable. To simplify the model construction, previous contributions assume that observations are tracked on common-frequency (CF) bands for all the involved receiver-satellite pairs. Such a model is referred to as CF PPP-RTK. However, the coexistence of legacy and modernized GNSS signal systems, together with the presence of outdated and updated receiver firmware, leads to not-common-frequency (NCF) cases where some of the involved receivers fail to track observations on certain frequencies. For such cases, the CF PPP-RTK model discards part of the observations so as to maintain the CF assumption. In this contribution, we refrain from making the CF assumption and extend the GNSS undifferenced and uncombined formulation to NCF cases. Such a NCF PPP-RTK model ensures that all observations contribute to the parameter estimation process, avoiding losing any information content in the data. As a result, our proposed NCF PPP-RTK avoids any potential reduction in both the availability and the precision of the corrections. To evaluate the positioning performance of the proposed model, we conducted three experiments with continuously operating reference station data in Hong Kong, Australia, and Europe. The superiority of the NCF PPP-RTK model over its conventional CF PPP-RTK version is illustrated in terms of both the time-to-first-fix and root mean square positioning errors.
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Data availability
The GNSS data used in this contribution are freely accessible via ftp://ftp.geodetic.gov.hk/, https://gnss.ga.gov.au/, https://epncb.oma.be/.
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Acknowledgements
The authors would like to thank Dr. Pengyu Hou for his insightful discussions on this research.
Funding
This work was funded by the National Natural Science Foundation of China (Grant No. 42022025). The corresponding author is supported by the CAS Pioneer Hundred Talents Program.
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CK processed the data. BZ proposed the method and designed the research. CK and AK analyzed the results and edited the text. CK and BZ wrote the manuscript.
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Ke, C., Zhang, B. & Khodabandeh, A. Extension of the undifferenced and uncombined CDMA PPP-RTK for not-common-frequency GNSS observations. GPS Solut 28, 102 (2024). https://doi.org/10.1007/s10291-024-01644-4
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DOI: https://doi.org/10.1007/s10291-024-01644-4