Positioning in Non-Terrestrial Networks

Abstract: In 5G communications, Non-terrestrial Network (NTN) is envisioned to complement Terrestrial Network (TN) to increase network availability, scalability and continuity. Positioning of User Equipment (UE) is critical for the operation of NTN. Currently, NTN uses Global Navigation Satellite System (GNSS) for positioning. However, the use of GNSS to complement NTN operation has some drawbacks such as higher cost and high-power consumption. The aim of this thesis work is to find an alternative solution to NTN positioning by evaluating a candidate positioning signal for NTN and to analyze the impact of different parameters on positioning accuracy. To this end, Positioning Reference Signal (PRS) in 5G NR is investigated for NTN positioning using different configurations. In addition, the impact of different satellite parameters and deployment scenarios on positioning accuracy has been analyzed in simulation. The effect of uncertainty in the satellites’ positions has also been investigated. The simulator is implemented on MATLAB and it is based on 5G NR positioning in Third Generation Partnership Project (3GPP) Release 16. The results show that good positioning accuracy of within a few meters can be reached using downlink time-difference-of-arrival (DL-TDOA) estimates in NTN. Increasing the bandwidth of PRS improves positioning accuracy. At high carrier-to-noise ratios, the number of transmitted PRS symbols have little influence on the accuracy performance, whereas increasing the sampling frequency can significantly enhance positioning accuracy. In addition, increasing the number of satellites used for positioning enhances the accuracy, whereas increasing the altitude of the satellites may degrade the accuracy. Moreover, the satellites deployment scenario has a noticeable impact on positioning accuracy. Finally, having imprecise knowledge of the satellites’ positions, even by only a few meters, is observed to affect the accuracy substantially as well.