DESIGN AND ASSESSMENT OF A LEO GNSS MINICONSTELLATION FOR POSITIONING, NAVIGATION, AND TIMING (PNT)

Recently, there has been a resurgent demand in the United Arab Emirates for more accurate positioning, navigation, and timing signals, especially for some targeted applications such as autonomous vehicles and flying taxis. The existing Global Navigation Satellite Systems (GNSS) provide real-time positioning accuracy for up to several meters, while the targeted applications require fast convergence of centimeterlevel positioning accuracy. Recent studies have shown that transmitting GNSS signals from a Low Earth Orbit (LEO) instead of a Medium Earth Orbit (MEO) would enhance positioning accuracy. The main objective of this thesis is to design and simulate an optimum scenario of a mini-LEO constellation transmitting GNSS signals in LEO and assess its performance using a GNSS simulator tool. The second objective is to evaluate the performance of a ground-based GNSS receiver receiving GNSS signals from LEO regarding the receiver’s time to lock, locking period, continuity, Position Dilution of Precision (PDOP) and 3D positioning accuracy. The final objective is to compare the performance of the simulated mini-LEO GNSS constellation with the existing MEO GPS and Galileo. Skydel GNSS simulator tool, single frequency L1/E1 ublox receiver, Systems Tool Kit (STK), and u-center software were used to conduct this research. The best simulated LEO scenario had a design consisting of 35 satellites at 800 km altitude, distributed into 5 planes, with 7 satellites in each plane, the planes were 45° apart and the satellites were 30° in each plane. The results showed a range of PDOP values from 2.1 to 3.3, 3D positioning accuracy of 5.86 m, and the time the receiver took to lock was about 1 minute with a maximum locking period of 3 minutes and with no continuity. The results obtained from the simulated LEO constellation assessed using the ublox receiver were no better than those of the simulated MEO GPS and Galileo. The main reason behind the obtained results is that the current GNSS receivers are not designed to cope with the higher dynamics of the satellites in LEO