G NR-Ntn Protocol Design Advances Full-Stack Performance in Challenging Networks

Researchers are increasingly focused on extending the reach of 5G connectivity beyond traditional terrestrial infrastructure, prompting investigation into Non-Terrestrial Networks (NTNs) utilising platforms like High Altitude Platforms and Unmanned Aerial Vehicles. Francesco Rossato, Mattia Figaro, and Alessandro Traspadini from the University of Padova, alongside Takayuki Shimizu, Chinmay Mahabal, Sanjeewa Herath et al from R&D InfoTech Labs, Toyota Motor North America Inc, detail the open challenges in designing full-stack protocols for 3GPP 5G NR-NTN networks. Their work is significant because it identifies critical considerations for the physical, MAC, and higher layers, paving the way for improved coverage in remote areas, enhanced emergency support, and optimised network performance in congested urban environments , and includes initial simulation results using ns-3 to demonstrate these impact.

The team achieved a detailed exploration of synchronization, duplexing, resource allocation, retransmissions, coverage, mobility management, routing, and network and transport layers, all crucial for effective NTN operation. Experiments show the impact of several key factors on 5G NR-NTN performance using the ns-3 simulation platform, a tool vital for evaluating network behaviour under realistic conditions. This research establishes a foundation for more advanced standardization efforts within 3GPP, addressing limitations in existing literature which often lacks empirical validation.

Low Earth Orbit (LEO) satellites, in particular, offer wide-area connectivity with relatively low latency, proving attractive for applications such as connected vehicles, automation, Internet of Things (IoT), aerospace, environmental monitoring, smart grids, and remote management. Furthermore, satellites can provide standalone broadband connectivity even without ground infrastructure, proving invaluable in disaster relief or isolated locations. This breakthrough reveals that satellites face unique challenges, including severe path loss, atmospheric attenuation from scintillation, rain, and clouds, and Doppler shifts due to orbital mobility, all of which complicate PHY/MAC procedures like channel estimation, resource allocation, scheduling, routing, and handover management. The research proves that larger coverage areas and increased terminal density in satellite networks can saturate available resources, necessitating substantial modifications to the 5G NR-TN protocol stack.

5G NR-NTN simulation using ns3-NTN module

The study pioneered the release of ns3-NTN, an open-source ns-3 module designed to simulate satellite communication networks with unprecedented fidelity. Unlike conventional link-level simulators, ns3-NTN facilitates full-stack, end-to-end simulations grounded in the latest 3GPP 5G NR-NTN specifications. Scientists engineered the module to incorporate 3GPP NTN path-loss models, channel characteristics, absorption calculations, and antenna models, all operating within an Earth-Centered, Earth-Fixed (ECEF) coordinate system. Crucially, the system delivers accurate satellite-specific propagation delay models, timing advance mechanisms, and adjusted Radio Resource Control (RRC) and Hybrid Automatic Repeat Request (HARQ) timers.

Experiments employed a rigorous validation process, comparing ns3-NTN’s performance against official 3GPP calibration results to ensure accuracy and reliability. This validation confirms ns3-NTN as a highly accurate and accessible tool for NTN simulations, addressing a significant gap in the field where experimental and simulation activities are often limited to well-funded entities with closed-source architectures. The approach enables researchers to verify results and simulation assumptions with greater transparency and customisation. Furthermore, the research team harnessed ns3-NTN to evaluate the performance of several 5G NR-NTN protocol implementations in representative NTN scenarios, focusing on key challenges like synchronisation. The team analysed relevant 3GPP Technical Documents (TDocs) from Working Groups 1, 2, and 3, specifically examining issues related to GNSS resilient operation, resource allocation, and HARQ enhancements, documented in Table I, to inform the simulation parameters and analysis.

5G NR-NTN Performance via ns-3 Simulation demonstrates promising

Experiments revealed that satellite communication networks present unique hurdles compared to traditional terrestrial networks, primarily due to increased path loss, atmospheric attenuation from scintillation, rain, and clouds, and significant Doppler shifts caused by orbital movement. Measurements confirm that the long propagation delays inherent in satellite networks complicate procedures like channel estimation, resource allocation, and handover management. Furthermore, the larger coverage areas of satellites, serving a greater number of terminals, can potentially saturate available network resources. Results demonstrate the importance of carefully considering Time Division Duplexing (TDD) with Guard Periods (GPs) to mitigate interference in NTN systems.

Simulations measured the impact of varying GP lengths, revealing their crucial role in maintaining signal quality and network stability. The team also recorded the performance of Hybrid Automatic Repeat reQuests (HARQs) processes for retransmissions, finding that the number of processes directly affects reliability in the face of challenging satellite links. Tests prove that differential delay in large satellite cells significantly impacts performance, necessitating robust channel estimation techniques. Measurements showed that the implementation of Transmission Control Protocol (TCP) mechanisms is vital for efficient data transfer in NTN environments. This breakthrough delivers a foundational understanding for future 3GPP 5G NR-NTN standardization activities and enhances the potential of satellite-integrated 5G networks for diverse applications like connected vehicles, IoT, and emergency communications.

5G-NR NTN Standardisation Challenges and Simulations require extensive

The authors acknowledge limitations in the scope of their simulations and suggest that future work should explore different TCP variants, including Multipath TCP, alongside cross-layer designs adapting to satellite dynamics. Further research could also focus on refining TCP parameters to better accommodate the significant propagation delays inherent in NTN environments. These findings highlight the potential of NTNs to extend 5G connectivity beyond traditional terrestrial infrastructure, though their integration presents considerable technical hurdles related to signal path loss, delay, and the Doppler effect. The presented research contributes to a growing body of knowledge aimed at overcoming these challenges and realising the full potential of satellite-integrated 5G networks.