Evaluation of precise point positioning using MADOCA-LEX via Quasi-Zenith satellite system

This paper describes the evaluation of precise point positioning (PPP) using the Quasi-Zenith Satellite System (QZSS) L-band Experiment (LEX) signal. The first QZSS, the Japanese regional satellite navigation system, was launched from Japan in September 2010. QZSS transmits augmentation signals to enhance the global navigation satellite system (GNSS) positioning accuracy. One of the QZSS augmentation signals is the LEX signal, the objective of which to realize centimeter-class positioning with its broadcasting data. The Japan Aerospace Exploration Agency began a test transmission of a MADOCA-LEX message, a new type of LEX message, in April 2013. MADOCA-LEX provides the satellite orbit and clock correction data of multi-GNSS using a state-space representation (SSR) format for real-time PPP. Unfortunately, the LEX signal cannot be received using the currently available commercial GNSS receivers. Moreover, for real-time applications, the LEX message contained in the LEX signal is required to be extracted for computing the user positions in real time. In this study, we have developed a novel technique for receiving and decoding the MADOCA-LEX message using a software GNSS receiver. We have developed a technique to decode the LEX messages without the use of an LEX signal tracking loop for estimating the code phase and the Doppler frequency of the LEX signal, however, with the aid of the conventional L1CA signal broadcasted simultaneously from the QZSS. We have confirmed the effectiveness of the proposed method through static and kinematic tests. We have determined the receiver positions with a distance root-mean-square error of within 10 cm, by using PPP with the MADOCA-LEX message in the real-time static test. We have also found that the proposed localization technique is effective for position estimation with the decimeter-level accuracy through a kinematic test in the open-sky environment.