Description
A Satellite Access Node (SAN) is a fundamental component of 3GPP-defined Non-Terrestrial Networks (NTNs), introduced to formalize the integration of satellite-based access into the 5G system. Conceptually, a SAN is the satellite-borne entity that implements the radio interface towards the User Equipment (UE). Its specific architecture and functional split can vary, leading to two primary implementations: the 'gNB-on-satellite' (regenerative) and the 'satellite as a relay' (transparent) models.
In the regenerative model, the SAN incorporates the full gNB (Next Generation NodeB) protocol stack, including the Radio Resource Control (RRC), Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC), Medium Access Control (MAC), and Physical (PHY) layers. In this architecture, the satellite acts as a full-fledged base station in space. It demodulates, decodes, processes, and re-encodes the uplink signals before transmitting them down to a ground-based gateway or core network. This reduces latency on the satellite-to-ground feeder link but requires more processing power on the satellite.
In the transparent (or bent-pipe) model, the SAN functions primarily as a radio frequency (RF) relay. It receives the RF signal from UEs on the uplink, performs frequency conversion and amplification, and retransmits it towards a ground-based gNB. In this case, the gNB is located on Earth, and the SAN does not process the baseband protocols. The SAN's characteristics, such as its orbit (Geostationary Earth Orbit - GEO, Medium Earth Orbit - MEO, Low Earth Orbit - LEO), beam footprint, and propagation delay, are critical parameters that the 5G NR air interface and protocols must adapt to. Key specifications like TS 38.108 define the radio transmission and reception requirements for SANs, while performance requirements are covered in specs like TS 38.101 and TS 38.521.
Purpose & Motivation
The standardization of the SAN addresses the growing need to extend 5G coverage to underserved and unserved areas where terrestrial infrastructure is economically or geographically challenging to deploy, such as oceans, deserts, and remote rural regions. Prior to 3GPP's work on NTN, satellite communication systems operated largely independently of cellular standards, requiring dual-mode devices and lacking seamless service integration. The SAN concept provides a standardized framework for satellite access to be a native part of the 3GPP ecosystem.
Its creation, prominently in Release 17, was driven by global initiatives for ubiquitous connectivity and disaster resilience. It solves the problem of access node definition in space by specifying the functional requirements and interfaces, enabling satellite operators to build compliant payloads and device manufacturers to support NTN connectivity. By defining SAN behaviors and the necessary adaptations in the NR protocol stack (e.g., for long delay, high Doppler), 3GPP ensures that a standard UE can connect to a satellite network with minimal modification, fostering a unified market for equipment and services.
Classification
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (57 CRs across 3 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 17, 3GPP introduced new performance requirements and test specifications for the Satellite Access Node (SAN) function, documented primarily in TS 38.108 and TS 38.181. This included defining general performance sections, specific demodulation requirements for the PRACH channel, and refining unwanted emission and output power accuracy requirements for different SAN types. The release also involved corrections and maintenance of the associated technical reports to solidify the SAN specifications for Non-Terrestrial Networks (NTN).
- Description of general performance part sections for SAN TS 38.108 TS 38.108CR0022
- Big CR on NTN SAN performance requirements (TS38.108, Rel-17) TS 38.108CR0024
- CR to TS 38.108: removal of NTN SAN output power accuracy requirements for the extreme test conditions, Rel-17 TS 38.108CR0011
- Corrections to SAN TS 38.108 TS 38.108CR0012
- CR for TS 38.108, Correct unwanted emission requirements applicability for SAN type 1-H TS 38.108CR0027
- CR on NTN SAN performance requirements (TS38.108, Rel-17) TS 38.108CR0036
+ 5 more changes
In Release 18, the new work for the Satellite Access Node (SAN) function focused on establishing detailed demodulation performance and minimum requirements for IoT services over Non-Terrestrial Networks (NTN), specifically for NB-IoT and eMTC. This included defining and correcting specific transmitter requirements, such as spurious emission limits and out-of-band blocking, for different SAN types. The enhancements also introduced missing SAN classes and completed conformance requirements to ensure robust operation in satellite access scenarios.
- Big CR to TS 36.108 for IoT over NTN SAN demodulation requirements introduction TS 36.108CR0006
- Big CR for 38.181 on NR NTN enhancement SAN demodualtion requirements TS 38.181CR0031
- CR on SAN demodulation requirements for NB-IoT over NTN TS 36.108CR0011
- draft CR: Introduction of SAN demodulation requirements for IoT-NTN TS 36.108CR0012
- (LTE_NBIOT_eMTC_NTN_req-Perf) CR on SAN demodulation requirements for NB-IoT over NTN TS 36.108CR0019
- (LTE_NBIOT_eMTC_NTN_req-Perf) CR: Completion of eMTC SAN demodulation requirements TS 36.108CR0020
+ 20 more changes
In Release 19, the standardization of the Satellite Access Node (SAN) function introduced new RF and demodulation requirements specifically for IoT-NTN and NR NTN operations, including support for the Ku band and channel bandwidths less than 5MHz. The release also defined new SAN types, such as Type 1-H and Type 2-O, and added specific performance requirements for features like PUCCH format 2 and PUSCH with inter-slot OCC. Furthermore, corrections and clarifications were made to SAN requirements for over-the-air (OTA) metrics including ACLR, in-channel selectivity, and reference sensitivity.
- (IoT_NTN_TDD) Big CR to 36.108 Rel19 SAN RF TS 36.108CR0038
- Big CR: Introduction of SAN demodulation requirements for IoT-NTN Phase 3 TS 36.181CR0035
- Big CR to TS 38.108 the SAN requirement of the NR NTN Ku band TS 38.108CR0131
- CR to 38.108 for SAN PUCCH format2 requirement with less than 5MHz TS 38.108CR0156
- (NR_NTN_Ph3-Perf) CR TS38.108 SAN Demodulation requirement with OCC0 TS 38.108CR0157
- CR for TS 38.181, Introduction on SAN diagram for SAN supporting regenerative payload TS 38.181CR0067
+ 14 more changes
Explore further
Broader topics and technologies where SAN plays a role.
Defining Specifications
3GPP specifications that define or reference SAN, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 33.876 vi01 | Technical Report on Certificate Management | Rel-18 |
| TS 36.108 vj10 | Satellite Access Node RF Requirements | Rel-19 |
| TS 36.181 vj30 | E-UTRA RF Test Methods for Satellite Access Node | Rel-19 |
| TS 36.214 vj00 | E-UTRA Physical Layer Measurements | Rel-19 |
| TS 38.101 vj31 | NR User Equipment Radio Transmissions | Rel-19 |
| TS 38.108 vj20 | NTN NR Satellite Access Node RF Requirements | Rel-19 |
| TS 38.181 vj10 | NR Satellite Access Node RF Testing | Rel-19 |
| TS 38.521 vj20 | NR Physical Layer UE Conformance Testing | Rel-19 |
| TS 38.741 vj00 | NTN L-/S-band for NR Technical Specification | Rel-19 |
| TS 38.762 vj00 | Dynamic MIMO OTA Test Methodology for NR FR1 | Rel-19 |
| TS 38.863 vj10 | NR NTN RF and Co-existence Spec | Rel-19 |
