Combined BDS, Galileo, QZSS and GPS single-frequency RTK

We will focus on single-frequency single-baseline real-time kinematic (RTK) combining four Code Division Multiple Access (CDMA) satellite systems. We will combine observations from the Chinese BeiDou Navigation Satellite System (BDS), European Galileo, American Global Positioning System (GPS) and the Japanese Quasi-Zenith Satellite System (QZSS). To further strengthen the underlying model, attention will be given to overlapping frequencies between the systems. If one can calibrate the inter-system biases, a common pivot satellite between the respective systems can be used to parameterize double-differenced ambiguities. The LAMBDA method is used for ambiguity resolution. The instantaneous (single-epoch) single-frequency RTK performance is evaluated by a formal as well as an empirical analysis, consisting of ambiguity dilution of precision (ADOP), bootstrapped and integer least-squares success rates and positioning precisions. The time-to-correct-fix in some particular cases when instantaneous RTK is not possible will also be analyzed. To simulate conditions with obstructed satellite visibility or when low-elevation multipath is present, various elevation cut-off angles between 10 and 40° will be used. Four days of real data are collected in Perth, Western Australia. It will be shown that the four-system RTK model allows for improved integer ambiguity resolution and positioning performance over the single-, dual- or triple-systems, particularly for higher cut-off angles.