Analysis of multi-GNSS with GPS and Galileo in multipath environments

In this report, the advantage of using multi-constellation GNSS-receivers in multipath environments is investigated. Multi GNSS in this work refers to the use of multiple satellite constellations with different types of signal on multiple frequency bands. The main objective is to study how the availability and accuracy of the position solution can be improved by simultaneous use of multiple GNSS. This work focuses on the GPS and Galileo satellite navigation systems. The study is based on simulations of the different types of signal and satellite constellations, and tests using a hardware simulator and two existing receivers. One of the receivers is a mass-market type of receiver and the other is a professional grade receiver. Two receivers with the ability to use both GPS and Galileo were evaluated. One of the receivers also has the ability to use two frequency bands simultaneously. The receiver tests show that the combination of GPS and Galileo do not always provide smaller position error than using the constellations individually. Combining measurements from both GPS and Galileo can theoretically be made in such a way that the position error for the combination is smaller than for the separate constellations. However, tests show that the measurements are not combined that way. Evaluations of different types of signal and constellations show that the performance may vary between receivers. Therefore, it was not possible, with existing receivers, to evaluate the variations in performance between different types of signal regarding their robustness to, for example, multipath propagation. However, theoretical evaluations show that the new GPS and Galileo signal types are more robust towards multipath propagation than the older signals. The combination of GPS and Galileo provides the availability of a larger number of satellites, which has the greatest advantage in scenarios with multipath propagation and signal blockage due to, for example, nearby buildings. In such situations, a combination of multiple GNSS could be necessary for determining a position. Evaluations of the basic constellations of GPS and Galileo show that Galileo has slightly better performance in Sweden and its neighbourhood in terms of satellite geometries and the number of visible satellites. With the current operational satellites, however, the performance is better with the full GPS constellation, since the Galileo constellation is not complete.