LEO-based Positioning: Foundations, Signal Design, and Receiver Enhancements for 6G NTN

TL;DR

The paper investigates LEO-based positioning as a complement or alternative to GNSS for 6G NR-NTN, identifying key challenges in repurposing communication-focused NTN for PNT. It proposes design enhancements including broad positioning beams, time-domain processing at the UE, and PRS scheduling from multiple satellites, supported by an NR-compliant simulation framework (LEO orbit, Tx/Rx architectures, and a positioning engine). Through analysis of a representative 840-satellite LEO constellation, PRS signaling strategies, and acquisition/combination techniques, the study demonstrates that PRS from multiple satellites and multi-symbol transmissions can achieve sub-10 m to GNSS-like accuracy under favorable bandwidths and measurement windows. These findings indicate that LEO-based NTN positioning can serve as a viable GNSS augmentation or standalone PNT service in 6G, with significant practical impact for global coverage and energy-efficient UE localization.

Abstract

The integration of non-terrestrial networks (NTN) into 5G new radio (NR) has opened up the possibility of developing a new positioning infrastructure using NR signals from Low-Earth Orbit (LEO) satellites. Compared to existing Global Navigation Satellite Systems (GNSS), LEO-based cellular positioning offers several advantages, such as a superior link budget, higher operating bandwidth, and large forthcoming constellations. Due to these factors, LEO-based positioning, navigation, and timing (PNT) is a potential enhancement for NTN in 6G cellular networks. However, extending the existing terrestrial cellular positioning methods to LEO-based NTN positioning requires key fundamental enhancements. These include creating broad positioning beams orthogonal to conventional communication beams, time-domain processing at the user equipment (UE) to resolve large delay and Doppler uncertainties, and efficiently accommodating positioning reference signals (PRS) from multiple satellites within the communication resource grid. In this paper, we present the first set of design insights by incorporating these enhancements and thoroughly evaluating LEO-based positioning, considering the constraints and capabilities of the NR-NTN physical layer. To evaluate the performance of LEO-based NTN positioning, we develop a comprehensive NR-compliant simulation framework, including LEO orbit simulation, transmission (Tx) and receiver (Rx) architectures, and a positioning engine incorporating the necessary enhancements. Our findings suggest that LEO-based NTN positioning could serve as a complementary infrastructure to GNSS and, with appropriate enhancements, may also offer a viable alternative.

Figures (6)

• Figure 1: (a) NTN positioning, navigation, and timing. (b) LEO constellation. (c) CDF of the number of visible LEOs considering UE drop near the equator (worst case scenario).
• Figure 2: Signal generation, and instances of transmission and reception (assuming 3 LEOs).
• Figure 3: Receiver block diagram capturing baseband processing at UE.
• Figure 4: TOA error performance: Probability of PRS detection for different SNRs and TOA error performance.
• Figure 5: Searching over multiple PRS occasions: (a) SNR evolution in time and the corresponding latency to acquire per satellite TOA considering 400 ms search window (1 & 5 MHz bandwidth, 1 PRS symbol in 1 ms slot, and maximum of 10 occasions).