Performance Analysis of an Improved GPS LNAV to Support Development of Low-Cost Real-Time PPP Systems with High Scalability and Availability

摘要

Highly scalable and available real-time precise satellite orbit and clock corrections are the prerequisite to the development of low-cost real-time Precise Point Positioning (PPP) system. At present, the Radio Technical Commission for Maritime Services (RTCM) State Space Representation (SSR) messages are commonly used for representing and disseminating real-time precise satellite orbit and clock corrections. Since RTCM SSR requires a continuous connection between the server and the user ends to transmit the high-rate corrections, real-time PPP positioning accuracy may be affected by the increasing satellite orbit and clock errors during correction outages caused by communication link corruptions, server malfunction, and so on. To better support the development of low-cost real-time PPP systems demanding both high precision and low costs, the improved Legacy Navigation messages (LNAV) is generated by estimating the satellite orbit parameters with International GNSS Service (IGS) ultra-rapid orbits as well as by estimating the satellite clock parameters with real-time correction streams. The improved LNAV has fully-consistent representation and user-end algorithms as the conventional LNAV from the GPS system but with significantly improved accuracy. The update rates of the improved LNAV are fully scalable to accommodate different low-cost real-time PPP systems in terms of communication bandwidth (costs) and accuracy. Furthermore, real-time precise satellite orbit and clock corrections are available for up to 2 hours when correction outages occur so that real-time PPP positioning accuracy can be maintained. In this study, the accuracy of improved LNAV is compared with the RTCM SSR corrections, and the quality degradation during correction outages is analyzed. The positioning performance of the improved GPS LNAV is explored using both static and kinematic datasets from the Android Nexus 9 tablet and U-Blox M8T receivers. The results indicated that the improved LNAV can provide corrections with sufficient accuracy to meet consumer application requirements and can provide high availability even during correction outages. It is concluded that the improved LNAV can be an effective alternative approach for delivering real-time precise corrections of high scalability and availability and can be applied to support the development of next-generation low-cost real-time PPP systems for mass-market applications.