Real-time precise point positioning utilising the Japanese quasi-zenith satellite system (QZSS) LEX corrections

The Quasi-Zenith Satellite System (QZSS) is a Japanese regional satellite navigation system (when fully deployed) consisting of several QZSS satellites in highly inclined elliptical orbits. This means that at least one satellite is constantly located at a high angle of elevation, which gives rise to the term 'quasi-zenith'. QZSS is a satellite-based augmentation system for the GPS and Galileo constellations, capable of transmitting navigation signals that are compatible and interoperable with both of these Global Navigation Satellite Systems (GNSS). In addition to the navigation signals, QZSS also transmits augmentation signals, e.g. the L-band Experimental (LEX) signal on the E6b frequency. The LEX signal is unique for QZSS that delivers correction messages - such as orbits and clock information - that enable Precise Point Positioning (PPP) for real-time applications. The aim of this research was to evaluate the availability of the QZSS LEX signal as well as the quality of the broadcast correction messages on the LEX signal for real-time PPP. The system was tested in both static and kinematic positioning mode in Melbourne in early March 2013. The results show that the availability of the LEX signal was 60% when the QZSS satellite elevation was at 30º; and above 90% when satellite was above 40º elevation. The quality of the PPP positioning estimates using the current LEX correction messages was limited by the accuracy of the satellite orbits and clocks transmitted on the LEX signal. The achievable PPP positioning accuracy in real-time using the current LEX corrections was at decimetre level.