New Network RTK Based on Transparent Reference Selection in Absolute Positioning Mode

Abstract

In this paper, the network real-time kinematic (NRTK) positioning method based on undifferenced (UD) observation corrections (abbreviated as URTK) are described, in which instantaneous ambiguity resolution can be carried out within rover’s precise point positioning (PPP) software, thus achieving position solutions equivalent to NRTK. The URTK method transforms the fixed double-differenced (DD) ambiguities of the reference network into UD ambiguities. With the transformed ambiguities, the residuals of the UD observation are used for interpolating the corrections at the user side. This approach breaks down the connections between the stations and satellites of the DD corrections in the current NRTK methods, such that corrections can be broadcast by the base station and automatically selected and optimized by a rover during the real-time kinematic (RTK) processing when the rover is transitioning into a more favorable subnetwork configuration, thus avoiding ambiguity reinitialization as a result of the change of reference. More importantly, this proposed approach provides a seamless integration of regional NRTK (PPP with regional augmentation) and global PPP-assisted kinematic surveying, which should be very useful for a wide range of applications. The key for realizing the improvements over standard NRTK is the development of a logical scheme that has the capability of rapid fixing of the single-differenced ionosphere-free ambiguity of the rover. Case studies at sea and on land demonstrate the advantages of this approach in terms of improvement in positioning accuracy, elimination of subsequent ambiguity reinitialization, and wider applications in the future.