GPS Solutions

, Volume 13, Issue 1, pp 43–56 | Cite as

Network-based geometry-free three carrier ambiguity resolution and phase bias calibration

  • Yanming FengEmail author
  • Chris Rizos
Original Article


Continuously operating reference stations (CORS) are increasingly used to deliver real-time and near-real-time precise positioning services on a regional basis. A CORS network-based data processing system uses either or both of the two types of measurements: (1) ambiguity-resolved double-differenced (DD) phase measurements, and (2) phase bias calibrated zero-differenced (ZD) phase measurements. This paper describes generalized, network-based geometry-free models for three carrier ambiguity resolution (TCAR) and phase bias estimation with DD and ZD code and phase measurements. First, the geometry-free TCAR models are constructed with two Extra-Widelane (EWL)/Widelane (WL) virtual observables to allow for rapid ambiguity resolution (AR) for DD phase measurements without distance constraints. With an ambiguity-resolved WL phase measurement and the ionospheric estimate derived from the two EWL observables, an additional geometry-free equation is formed for the third virtual observable linearly independent of the previous two. AR with the third geometry-free model requires a longer period of observations for averaging than the first two, but is also distance-independent. A more general formulation of the geometry-free model for a baseline or network is also introduced, where all the DD ambiguities can be more rigorously resolved using the LAMBDA method. Second, the geometry-free models for calibration of three carrier phase biases of ZD phase measurements are similarly defined for selected virtual observables. A network adjustment procedure is then used to improve the ZD phase biases with known DD integer constraints. Numerical results from experiments with 24-h dual-frequency GPS data from three US CORS stations baseline lengths of 21, 56 and 74 km confirm the theoretical predictions concerning AR reliability of the network-based geometry-free algorithms.


GNSS Three carrier ambiguity resolution Phase bias calibration Network adjustment 



This work was carried out with financial support from the Cooperative Research Centre for Spatial Information (CRCSI) project 1.4—“Delivering precise positioning services in regional areas”, 2007–2010.


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Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  1. 1.Queensland University of TechnologyBrisbaneAustralia
  2. 2.The University of New South WalesSydneyAustralia

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