Ground-based PPP-RTK for pseudolite systems

Global navigation satellite systems (GNSS) can provide high-accuracy positioning services in the open environment, while they have poor performance in shadowed regions. Pseudolite (PL) systems, with flexible deployment, can carry on the role of GNSS to provide high-accuracy positioning services in the case of GNSS failure. Ground-based precise point positioning (gPPP) for pseudolite systems allows a user to use a stand-alone receiver to achieve centimeter-level positioning, but without integer ambiguity resolution (IAR). The purpose of this work is to transfer the GNSS precise point positioning-real-time kinematic (PPP-RTK) technology to a ground-based pseudolite system, referred to as gPPP-RTK, for faster convergence and higher accuracy compared to gPPP by achieving IAR. However, the estimation of transmitter phase biases (TPBs) is the core for gPPP-RTK. Therefore, based on our independently developed pseudolite system, we propose a method to estimate the TPBs and analyze their characteristics. In this study, it is shown that the TPBs are rather stable in time unless the PL system is restarted. As a result, the TPBs do not need to be broadcast to users frequently. A real-world gPPP-RTK experiment demonstrated that the convergence time dramatically shortened the horizontal and vertical components by 42% and 59%, respectively, compared with gPPP. Furthermore, gPPP-RTK showed a better positioning accuracy of 1.86 and 4.06 cm in the horizontal and vertical components, respectively, compared with that of 2.00 and 10.00 cm for gPPP. The performances of convergence time and positioning accuracy in the vertical component are significantly better than that in the horizontal component.