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.

Popular Abstract

Non-Terrestrial Network (NTN) is a network that includes non-terrestrial flying objects. High Altitude Platform Systems (HAPS), air-to-ground networks and satellite communication networks are all NTN systems. A satellite communication network uses satellites to communicate with one another, as well as with ground stations and User Equipment (UE). These satellites can be Low Earth Orbit (LEO) satellites, Medium Earth Orbit (MEO) satellites or Geostationary Earth Orbit (GEO) satellites. Nowadays, there is an interest in integrating satellite networks with 5G systems. NTN has the advantages of service continuity, scalability and availability, which will support 5G systems to achieve their challenging use cases. Service continuity means that the network can provide connection to UE at anytime and anywhere. Service scalability means that the network can maintain good service despite an increase in traffic load because of the support of NTN. Service availability means that the network is always available even in cases of disasters or similar situations. However, to facilitate these functionalities, the NTN needs to know the UE position.

In 3rd Generation Partnership Project (3GPP) Release 17, UE positioning in NTN is performed with the existing Global Navigation Satellite System (GNSS). GNSS is a navigation satellite constellation that provides global or regional coverage and can be used for positioning purposes. Using GNSS in NTN has some drawbacks. Firstly, the UE device must have two separate receivers: one for positioning (GNSS receiver) and another one for communication (NTN receiver). Secondly, the use of dual receivers may incur high power consumption at the UE. Therefore, it is highly desirable to extend the communication capability of NTN to enable positioning, so that the usage of GNSS is no longer required.

Observed Time Difference of Arrival (OTDOA) is one of the cellular positioning techniques that uses the time difference between the arrival of Positioning Reference Signals (PRS) for the computation of the location of the UE. In this thesis, an NTN simulator has been implemented in MATLAB using OTDOA as the positioning method. The NTN simulator is then used to investigate the appropriate PRS configuration in NTN. In addition, the impact of several factors on the positioning accuracy of the UE has been examined. It is shown that using OTDOA as the positioning method and PRS as the reference signal in NTN result in good positioning accuracy of within several meters. Moreover, it is shown that positioning accuracy varies depending on the channel model and satellite parameters used. Considering the satellite as a moving object, it is observed that inaccurate knowledge of the satellite locations results in substantial degradation of UE positioning estimation accuracy. For example, if the actual satellite positions are perturbed randomly from their nominal positions according to a zero mean normal distribution with a standard deviation of 2 meters, 50% of the UE will experience up to 50% more error in the estimated position.

• author: Emara, Soha
• supervisor: Buon Kiong Lau
• organization: Department of Electrical and Information Technology
• course: EITM02 20211
• year: 2021
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: positioning, 5G, satellite, NTN
• report number: LU/LTH-EIT 2021-838
• language: English
• id: 9061053
• date added to LUP: 2021-08-12 09:55:40
• date last changed: 2021-08-12 09:55:40