Session A1: Alternatives, Backups, Complements to GNSS

Leveraging 5G-NR and DVB-S2X for Positioning in LEO-NTN
Harshal More, Dept. Electronics Engineering, Torvergata University; Francesco Menzione, Ottavio Picchi, Joint Research Centre, European Commission; Mauro De Sanctis, and Ernestina Cianca, Dept. Electronics Engineering, Torvergata University
Location: Beacon A

Recently, the use of Low Earth Orbit (LEO) satellite constellations for Positioning, Navigation, and Timing (PNT) applications is emerging as a critical area of research, due to their various advantages and ability to address the limitations and vulnerabilities of traditional Global Navigation Satellite Systems (GNSS). On the other hand, various studies are comparing the performance for the adoption of 5th Generation New Radio (5G-NR) and Digital Video Broadcasting Second Generation Satellite Extensions (DVB-S2X) for future LEO based Non-Terrestrial Networks (NTN) system. Both protocols are excellent candidates for modern satellite communications deployments, due to their high spectral efficiencies, therefore, the assessment of their suitability to also provide PNT services is of paramount importance.
In line with current trends, this paper explores the feasibility of utilizing these well-established communication protocols to create dual-purpose PNT infrastructures within LEO-based NTNs. In our study, we rely on a multi-tier architecture that utilizes GNSS as a backbone. LEO satellites are equipped with space-borne GNSS receivers that function as on-board Orbit Determination and Time Synchronization (ODTS) systems allowing precise determination and dissemination of orbit and time information. The detailed frame structure of these protocols is leveraged by specifically exploiting the Synchronization Symbols (SS), such as the Start of Super-Frame (SOSF) and Super-Frame Format Indicator (SFFI) in DVB-S2X, as well as the Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS) in 5G-NR. These SS blocks are analogous to GNSS pseudo-random noise (PRN) codes, making them possible for generating pseudorange-like measurements. Moreover, open field in the frames and the high spectral efficiency of both protocols enables to convey LEO satellite ODTS information, and supplementary navigational data essential for end-users to solve the localization problem.
It is well known that 5G-NR downlink can provide on-demand dedicated positioning services through the Positioning Reference Signal (PRS). However, this comes with an additional cost in terms of resource allocation, which can reduce communication capacity. To validate this approach, a comparative analysis of acquisition and tracking performance across 5G-NR (SS), 5G-NR (PRS), DVB-S2X, and GNSS (GPS C/A, L1) is conducted. The evaluation focuses on key performance metrics, including Mean Acquisition Time (MAT), Receiver Operating Characteristics (ROC) for acquisition, and the Cramér-Rao Lower Bound (CRLB) for tracking to assess pseudorange estimation accuracy.
Considering the differences in operating signal-to-noise ratios (SNR) for communication and navigation, the ROC analysis is conducted statistically, providing insights into signal acquisition by assessing the probability of detection and false alarm for varying thresholds in noisy environments. This statistical model allows for rapid acquisition performance assessment, enabling a trade-off between performance and receiver complexity. Additionally, the application of statistical models, traditionally used for GNSS signals, to communication signals is a key contribution of this paper. MAT for each protocol is calculated based on time shift, frequency hypotheses, coherent integration time, probability of detection and probability of false alarm offering a detailed evaluation of signal acquisition time for all protocols. Moreover, an analysis of the Auto-Correlation Functions (ACF) for 5G and DVB-S2X synchronization sequences is carried out to provide some recommendations for the receiver design for PNT purpose.
Open and closed loop pseudorange accuracy estimated using CRLB show that GNSS maintains superior tracking accuracy due to its continuous PRN transmissions, whereas 5G-NR (SS) and DVB-S2X provide reasonable accuracy within LEO-NTN environments. Pseudorange accuracy estimation using DVB-S2X varies with different roll-off factor, bandwidth and length of SS. One of the key uncertainties surrounding 5G PRS, both for terrestrial and NTN systems, is how to balance the resource costs between positioning and communication. Therefore, a thorough analysis of CRLB for PRS ranging accuracy for various configurations (different comb structures) PRS signals, along with the related resource costs, is a valuable addition to this paper.
The paper concludes that integrating navigation services within the 5G-NR and DVB-S2X frameworks shows significant potential for future LEO-NTN systems. Although these protocols exhibit certain limitations when compared to GNSS, they offer a viable solution for dual-purpose NTN infrastructures that support both communication and navigation. This work also addresses the impact of SS length and periodicity, bandwidth on positioning accuracy. The proposed analysis lays the groundwork for optimizing these protocols to design cost-effective, sustainable, dual-purpose LEO satellite systems capable of delivering complementary PNT services while maintaining high communication performance.