Satellite Access

Description

Satellite access in 3GPP refers to the direct radio connectivity established between a User Equipment (UE) and a satellite, without requiring a terrestrial relay in between. The satellite acts as an access node — functionally analogous to a gNB or ng-eNB — that serves the UE over a radio interface. This concept is central to the integration of Non-Terrestrial Networks (NTN) into the 5G system and beyond, and it is studied and specified across releases starting with Rel-19. The relevant specifications include TS 22.261 (Service requirements for the 5G system) and TR 22.870 (Study on 5G-Advanced and beyond satellite access), which define service requirements and use cases.

Architecturally, satellite access can be realized in several ways. In a transparent (bent-pipe) architecture, the satellite simply relays the radio signal between the UE and a ground-based gateway that connects to the core network; the satellite does not terminate any protocol layers. In a regenerative architecture, the satellite carries part or all of the gNB functionality on board, terminating the NR Uu interface and possibly the NG interface towards the core network. The choice of architecture affects latency, link budget, and handover complexity. The satellite may operate in Geostationary Orbit (GSO) or Non-Geostationary Orbit (NGSO), including Low Earth Orbit (LEO) and Medium Earth Orbit (MEO), each with different propagation delays and Doppler characteristics.

Key technical challenges addressed by satellite access include large propagation delays (especially for GSO, where round-trip time can exceed 500 ms), significant Doppler shifts for NGSO constellations, and intermittent connectivity due to satellite movement. 3GPP solutions include timing advance adjustments, HARQ disabling or adaptation, and enhanced mobility procedures to handle frequent satellite handovers. The UE must also manage power consumption and antenna pointing, particularly for handheld devices with limited link budget.

Satellite access enables service continuity in remote, rural, maritime, and aeronautical environments, as well as disaster recovery scenarios where terrestrial infrastructure is damaged. It supports both broadband and IoT services, with Narrowband IoT (NB-IoT) and eMTC over satellite being studied for massive machine-type communications. The integration with the 5G core allows unified authentication, policy control, and charging, treating satellite access as just another access technology within the 5G convergence framework.

In Rel-19 and Rel-20, satellite access is further refined to support direct UE-to-satellite communication for commercial handsets, reducing dependence on specialized satellite terminals. This includes regulatory, spectrum, and interference management considerations. The work also addresses network selection, roaming, and emergency services over satellite, ensuring that satellite access is not a siloed technology but a fully integrated part of the 3GPP ecosystem.

Purpose & Motivation

Satellite access exists to extend 3GPP mobile services to areas where terrestrial network deployment is economically or physically infeasible, such as oceans, deserts, mountains, and remote rural regions. Traditional cellular networks rely on base stations connected by fiber or microwave backhaul, which cannot reach these areas. Satellite access solves this by using satellites as access nodes, providing coverage from the sky and enabling ubiquitous connectivity.

Historically, satellite communication was separate from cellular standards, using proprietary protocols and specialized terminals. The motivation for integrating satellite access into 3GPP was to leverage the economies of scale of cellular chipsets, enable seamless roaming between terrestrial and satellite networks, and provide a unified service experience. Earlier releases (Rel-15 to Rel-18) studied NTN scenarios, but Rel-19 and Rel-20 mark a shift towards direct UE-to-satellite connectivity for mainstream devices, including smartphones.

The limitations of previous approaches included high terminal cost, lack of interoperability, and no support for 3GPP security and policy frameworks. Satellite access within 3GPP addresses these by reusing the 5G NR radio interface, core network procedures, and identity management, making satellite just another access technology in the converged network.