Multi-GNSS Point Positioning: systems, signals and ionospheric models analysis

GNSS (Global Navigation Satellite Systems) have been increasingly employed in activities that require position estimates. In addition to the widespread North American GPS (Global Positioning System), satellites from three similar systems are currently orbiting the Earth: GLONASS, developed by the former Soviet Union, which has now a full constellation, and the European Galileo and Chinese BDS, both under implementation phase and with plans to reach full constellation by 2020. Through their navigation messages, GPS and Galileo send parameters for ionospheric delay correction at global level, which are used in the Klobuchar and NeQuick G models, respectively. The tendency is for these four systems to work together at the user level, improving the positioning availability and accuracy. In this research we aimed to evaluate the accuracy of the Point Positioning (with pseudoranges and precise ephemeris) using the different systems and frequencies separately, as well as their integration in the so-called multi-GNSS positioning. In addition, the performance of the Klobuchar and NeQuick G models in the Brazilian region and worldwide was analyzed. Three experiments were performed; in the first one, it was verified that the multi-GNSS positioning in relation to GPS positioning can show an improvement of approximately 11% in unobstructed environments and up to 60% in environments with a high degree of obstruction. It was verified that the improvement rate is directly linked to the multipath level of the station (correlation of 0.74). Based on the results obtained in the second and third experiments, which evaluated the performance of the Klobuchar and NeQuick G, the models showed an overall relative error of approximately 49 and 40%, respectively. The use of the Klobuchar model is recommended for periods and regions of high ionospheric activity, since the ionospheric delay is usually overestimated. The NeQuick G model, on the other hand, is recommended for regions and periods of low ionospheric activity, since the ionospheric delay is usually underestimated. (AU)