Locata-based precise point positioning for kinematic maritime applications

Abstract

The GPS-precise point positioning (PPP) is still not as popular as network-based real-time kinematic (N-RTK) for engineering kinematic applications based on differential positioning principles for several reasons. One is the fact that the accuracy of kinematic GPS-PPP is lower than N-RTK solutions. The second reason is that GPS-PPP requires a comparatively long initialization period. In order to overcome such shortcomings, a new PPP approach augmented by a ground-based positioning system such as "Locata" is proposed in this paper. The new approach is referred to as Locata/GPS-PPP. Locata's ground-based technology has rapid geometry change for kinematic applications; thus, the proposed approach is able to provide high-accuracy solutions with faster initialization. In the proposed Locata/GPS-PPP approach, the Locata and GPS carrier phase measurements are processed simultaneously in a tightly combined mode and the carrier phase ambiguities are resolved as floating-point values on an epoch-by-epoch basis in order to avoid the need for cycle-slip repair. In order to evaluate the system performance, a kinematic field trial was conducted on Sydney Harbor. A Locata transmitter network was setup on the fringes of Sydney's CBD. The experiment demonstrated that the initial convergence time of the integrated Locata/GPS-PPP filter is only 10 s, which is significantly faster than the conventional GPS-PPP method. Comparison of the proposed method with the GPS-PPP and Locata-single point positioning (SPP) approaches was conducted. The results confirm that the Locata/GPS-PPP approach can achieve centimeter-level accuracy for horizontal positioning which improves 36.4 and 68.8 % over Locata-SPP and GPS-PPP. The results validate the effectiveness of the proposed approach for high-accuracy maritime applications.