Multi-GNSS Precise Point Positioning Using GPS, GLONASS and Galileo

A Global Navigation Satellite System (GNSS) refers to a global, satellite-based, allweather, 24-hour operational radio-navigation and time transfer system that is designed to provide positioning, timing and navigation (PNT) services primarily for military as well as civilian applications.In recent years, a positioning method known as Precise Point Positioning (PPP) has attracted broad interest in scientific research and engineering applications, as it does not require a reference station, reduces labor and equipment costs and simplifies field work.PPP, however, requires a long convergence time of 30 minutes or more in order to ensure centimeter level positioning accuracy, as PPP provides float ambiguity resolution due to the fact that ambiguity terms are not integer numbers because of satellite and receiver un-calibrated hardware delay biases.Although the main issue with the PPP method is its long convergence time, further improvements in the positioning accuracy especially for short observing-session durations is also expected.In this thesis, the impact of combining GPS, GLONASS and Galileo on the solutions of the positioning accuracy and convergence time problems is investigated.For this purpose, specific experiments are conducted using GPS, GLONASS and Galileo measurements collected at Multi-GNSS Experiment (MGEX) stations.First, the performance of the PPP method is analyzed in both static and kinematic modes for the following scenarios: GPS-only, combined GPS/GLONASS and combined GPS/GLONASS/Galileo.Secondly, the iii positioning solutions obtained with different precise satellite orbit and clock products of three IGS MGEX analysis centers are compared since at the time of writing, there was no combined precise product available.Thirdly, the performance of GPS-only, combined GPS/GLONASS and combined GPS/GLONASS/Galileo PPP solutions are demonstrated under different elevation cutoff angles (15°, 25° and 35°) to simulate constrained environments.Furthermore, the performance of GPS-only, combined GPS/GLONASS and combined GPS/GLONASS/Galileo PPP solutions from 1-hour, 2-hour and 3-hour observing-session durations are compared to analyze how the observing-session duration affects the positioning accuracy.Lastly, the performance of PPP and long baseline Differential GPS (DGPS) with ionosphere and troposphere elimination are compared through the use of combined GPS/GLONASS/Galileo measurements in order to compare the impact of the multi-GNSS combination on the PPP and DGPS methods.According to the numerical results, it is found that combined GPS/GLONASS improves both the positioning accuracy and convergence time over GPS-only while combined GPS/GLONASS/Galileo may either improve or worsen the positioning accuracy and convergence time over combined GPS/GLONASS, which depends on the number of Galileo satellites used.