New Radio – Non-Terrestrial Network

Description

NR-NTN (New Radio – Non-Terrestrial Network) is a 3GPP initiative that adapts the 5G New Radio (NR) air interface for operation over non-terrestrial platforms such as Low Earth Orbit (LEO) satellites, Geostationary Earth Orbit (GEO) satellites, High Altitude Platforms (HAPs), and Unmanned Aerial Vehicles (UAVs). Introduced in Release 20 and specified in 3GPP TR 38.742, NR-NTN aims to deliver 5G services directly via satellite, eliminating the need for specialized user terminals and enabling seamless integration between terrestrial and non-terrestrial networks.

The architecture of NR-NTN builds upon the existing 5G core network and NG-RAN framework. A satellite or HAP acts as an NTN node, which can function as a gNB (gNodeB) or as a relay. The NTN node connects to the 5G Core via a feeder link, while user equipment (UE) communicates over a service link. The large propagation delays and Doppler shifts inherent in satellite links require modifications to NR procedures, including timing advance, HARQ, and random access. NR-NTN supports both transparent and regenerative payload architectures: in a transparent payload, the satellite only amplifies and frequency-converts the signal, while in a regenerative payload, the satellite carries full gNB functionality.

Key technical challenges addressed by NR-NTN include extended round-trip times (up to hundreds of milliseconds for GEO), high Doppler frequency shifts (especially for LEO), and spot beam coverage. To handle these, 3GPP defines enhancements such as extended timing advance ranges, HARQ process adaptations, and beam-specific scheduling. The use of higher frequency bands (e.g., Ka-band, Ku-band) and the need for precise ephemeris data for satellite tracking are also integral to NR-NTN design.

NR-NTN enables several use cases: ubiquitous coverage in unserved or underserved areas (oceans, deserts, mountains), disaster relief communications, maritime and aeronautical connectivity, and backhaul for terrestrial networks. It also supports Internet of Things (IoT) devices via satellite, extending the reach of massive IoT. The integration with 5G core ensures that NTN is not a separate network but an extension of the 5G ecosystem, allowing unified management, security, and service continuity.

In Release 20, NR-NTN specifications in TR 38.742 provide the foundational study on NR support for NTN, covering deployment scenarios, channel models, and required adaptations. Subsequent releases are expected to refine and expand capabilities, including interworking with terrestrial networks, mobility management across satellite beams, and support for higher throughput and lower latency.

Purpose & Motivation

NR-NTN exists to extend 5G New Radio coverage to areas where terrestrial infrastructure is impractical or impossible to deploy, such as remote landmasses, oceans, and the sky. Traditional terrestrial networks rely on fiber and cell towers, which are economically unfeasible in sparsely populated regions. Satellite communication has historically been proprietary and incompatible with cellular standards, requiring specialized terminals. NR-NTN solves this by standardizing satellite access as part of 5G, enabling mainstream 5G devices to connect via satellite with minimal modifications.

The motivation for NR-NTN stems from the growing demand for global connectivity, the need for resilient communications in disaster scenarios, and the commercial potential of satellite constellations (e.g., Starlink, OneWeb). Previous approaches like 3GPP's earlier study on NTN in Release 15/16 focused on adapting LTE for satellite, but NR-NTN leverages the flexibility of 5G NR to better handle the challenges of non-terrestrial links. By integrating NTN into the 5G ecosystem, operators can offer seamless roaming between terrestrial and satellite networks, ensuring service continuity and expanding coverage without deploying costly ground infrastructure.