RTT NTN-Based Positioning With a Single Satellite in 6G: A Geometric Framework
TL;DR
The results show that accurate positioning can be achieved with as few as two RTT measurements, while additional measurements improve accuracy, particularly at lower LEO altitudes, and integration with the 5G NR signaling is discussed in detail, showing that only minor extensions are required.
Abstract
This paper presents a geometric and probabilistic framework for localizing static User Equipments (UEs) in Non-Terrestrial Networks (NTNs) using multiple Round-Trip Time (RTT) measurements from a single Low Earth Orbit (LEO) satellite. Motivated by the robustness and low complexity of RTT in 3GPP NTN systems and by the limitations of GNSS in low-cost devices, the approach exploits satellite mobility to transform time-separated RTT measurements into geometric constraints modeled via ellipsoidal and conic representations. Closed-form expressions relate RTT errors to uncertainties in range, angle-of-arrival, and UE position. A novel Region-of-Interest (RoI) metric is introduced to characterize single-satellite geometry, enabling the derivation of the likelihood function and a maximum-likelihood positioning algorithm. The impact of key parameters–number of measurements, satellite altitude, and RTT accuracy–is analyzed. Validation of the proposed multi-RTT technique is carried out by comparing it with simulation results and a well-known RTT-and-Doppler scheme. The close agreement with the simulation results confirms the validity of the proposed approach. The results further show that accurate positioning can be achieved with as few as two RTT measurements, while additional measurements improve accuracy, particularly at lower LEO altitudes. Finally, integration with the 5G NR signaling is discussed in detail, showing that only minor extensions are required.