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Non-Terrestrial Networks in 5G Systems

At a glance
  • What it is: satellite and other non-terrestrial access that reuses the 5G system and the NR protocol stack, with differences concentrated in the radio.
  • In this section: the NTN system model, radio-layer adaptations, system information for media, MBS over NTN and what each page adds.

How it works​

NTN reuses the 5G system and the NR protocol stack; the differences are concentrated in the radio and in a small number of architecture roles.

Key specifications: 3GPP TR 38.811 (Study on New Radio (NR) to support non-terrestrial networks), TR 38.821 (Solutions for NR to support NTN), TS 38.300 (NR overall description, NTN aspects), TR 38.863 (NTN related RF and co-existence aspects). For 5G Broadcast, see also ETSI TS 103 720 (5G Broadcast system for linear TV and radio; LTE-based 5G terrestrial broadcast system). Release 19 also adds an LTE downlink-only band (1467 to 1492 MHz, ITU Region 3) for 5G Broadcast via a GSO satellite, with UE and satellite access node RF requirements for a 10 MHz PMCH in TS 36.102 and TS 36.108 (TR 21.919 V19.0.0 clause 5.4.1, work item LTE_band_5G_bcast_GSO; in the two specifications the band is band 246, clauses 5.2 and 5.3C of V19.5.0). Release 20 adds 3 MHz and 5 MHz channel bandwidths for band 246 (TS 36.102 V20.0.0 and TS 36.108 V20.0.0, clause 5.3C).

NTN system model and terminology​

  • Feeder link / service link. The service link is the wireless link between the NTN payload and the UE; the feeder link is the wireless transport link between the NTN Gateway and the NTN payload (TS 38.300 clause 3.2). To accommodate the propagation delay, several timing relationships are enhanced by a Common Timing Advance and configured offsets (TS 38.300 clause 16.14.2.1).
  • Transparent vs regenerative payload. The NTN payload, on board a satellite or high altitude platform station, is a TNL node (transparent payload) or a gNB (regenerative payload) (TS 38.300 clause 3.2). The transparent payload forwards the radio protocol between the service link and the feeder link; the regenerative payload terminates the Uu, NG and Xn interfaces, and may terminate inter-satellite links towards other regenerative payloads (TS 38.300 clause 16.14.1).
  • Cells and service links. NTN can provide Earth-moving, quasi-Earth-fixed and Earth-fixed cells, supported by three types of service link: Earth-fixed beams cover the same area all the time (e.g. GSO satellites); quasi-Earth-fixed beams cover one area for a limited period and another area later (e.g. NGSO satellites with steerable beams); Earth-moving beams slide over the Earth surface (e.g. NGSO satellites with fixed beams). A Tracking Area corresponds to a fixed geographical area, and a Mapped Cell ID corresponds to a fixed geographical area (TS 38.300 clauses 3.2, 16.14.1 and 16.14.5). These cell types drive the handover models on the Mobility Aspects for NTN page.
  • GNSS at the UE. In this release, the UE supporting NTN is GNSS-capable, and NTN is only applicable to FDD (TS 38.300 clause 16.14.1).

Radio-layer adaptations for NTN​

The long, variable delay and the large Doppler shift on fast NGSO links are handled mainly at the physical and MAC layers, with assistance signalled in system information: a large, UE-specific timing advance computed from GNSS position and satellite ephemeris (plus a network-broadcast common component, anchored to an epoch time with a validity window); Doppler pre-compensation on the service link, computed by the device from geometry; a k-offset scheduling offset so uplink grants and other timing relationships remain valid despite the long round trip; and HARQ/RRC/MAC timers adapted for round trips that can far exceed terrestrial values, with some HARQ processes disabled and reliability moved to higher layers.

NTN system information for media delivery​

Two system information blocks are central to media over NTN:

  • SIB19 carries the NTN assistance information a device needs to acquire and track a satellite cell: serving-cell (and optionally neighbour-cell) ephemeris, common timing advance parameters, the k-offset, the epoch time and its validity duration, and the cell reference location. SIB19 was introduced with the Release 17 NTN work in TS 38.331.
  • SIB27, introduced in Release 19 of TS 38.331, contains the intended service areas (ISA) of MBS broadcast services in an NTN cell, each given as a polygon or a circle (TS 38.331 V19.4.0 clause 6.3.1); see MBS Broadcast NTN.

Carrying MBS over NTN​

TS 23.247 Release 19 states that transmission of a Broadcast MBS Session is supported over NR non-terrestrial networks (TS 23.247 V20.0.0 clause 4.1):

  • Broadcast MBS session. Delivered with 5GC Shared MBS traffic delivery and PTM delivery only, and receivable in RRC_IDLE, RRC_INACTIVE and RRC_CONNECTED (TS 38.300 V19.4.0 clause 16.10.1). Over NR NTN, Release 19 adds the NR NTN Intended Service Area, carried from the 5G Core to NG-RAN in the MBS service area and to the UE in SIB27, which can restrict the MBS service area to an area smaller than a cell (TS 23.247 V20.0.0 clauses 4.1 and 6.21; TS 38.300 V19.4.0 clauses 16.14.12 and 16.14.5). TR 21.919 V19.0.0 clause 5.1.1 (NR_NTN_Ph3) describes this as support for multicast and broadcast services when the intended service area is smaller than a cell, through enhanced SIB signalling and core-to-NG-RAN signalling; the specification texts checked define the ISA for the broadcast MBS session only.
  • Multicast MBS session. NG-RAN is the decision point for switching between PTP and PTM, and the UE receives it in RRC_CONNECTED, or in RRC_INACTIVE with PTM. TS 23.247 has no NTN clause for the multicast MBS session; TS 38.321 has, since Release 17, a multicast DRX HARQ timer for non-terrestrial networks that adds the UE-gNB round trip (TS 23.247 V20.0.0 clause 4.1; TS 38.300 V19.4.0 clause 16.10.1; TS 38.321 V17.15.0 and V19.4.0 clause 5.7).

Release context​

  • Release 17, 5GSAT_ARCH. The 5G Core gained RAT types that distinguish satellite configurations (LEO, MEO, GEO, other), a new 5QI for satellite access and backhaul, and support for satellite backhaul with constant delay only (TR 21.917 V17.0.1 clause 5.1.1).
  • Release 18, 5GSATB. Dynamic satellite backhaul categories (DYNAMIC_GEO, DYNAMIC_MEO, DYNAMIC_LEO and DYNAMIC_OTHERSAT) were defined, and a UE can use a UPF on board a GEO satellite for edge computing and local switching (TR 21.918 V18.0.0 clause 5.1).
  • Release 20, not yet in a TR 21.9xx report. TS 22.261 V20.8.1 clause 6.46.2 has a requirement that a 5G system supporting satellite access and Broadcast Services delivers Media Broadcast to a UE that is not registered, subject to regulatory requirements and operator policy (change history: CR 0835, Release 20). TS 23.501 V20.3.0 clause 5.43.3 specifies local switching for UE-to-UE communications via a UPF deployed on a GEO satellite, for 5G VN DNNs and slices, and its change history lists CR 6613, "Clarification on local switching capability of UPF on board satellites". The 5G Core procedures for the unregistered-UE broadcast requirement were not checked. In the 3GPP work plan of 28 September 2026 the Release 20 satellite access work is the item 5GSAT_Ph4 (Satellite access Phase 4), with the stage 1 item 5GSAT_Ph4-REQ (TS 22.261) and the stage 2 item 5GSAT_Ph4-ARC (WID SP-260423; TS 23.401, TS 23.228, TS 23.167, TS 23.203, TS 23.501, TS 23.502 and TS 23.503).

What each page adds​

  • Mobility Aspects for NTN sets out three deployment models (single NTN operator; common NTN/TN operator; independent operators) and what Release 19 specifies for mobility in each: Earth-fixed, quasi-Earth-fixed and Earth-moving cells, time- and location-based conditional handover, the satellite switch with re-synchronization and the feeder link switchover.
  • MBS Multicast over NTN sets out requirements for multicast over NTN, with the gNB switching each UE between PTP and PTM, against what Release 19 specifies.
  • Mobility for MBS Multicast over NTN sets out what Release 19 provides, UE by UE, when multicast receivers move over NTN (it has no group handover), distinguishing mobility triggered by satellite motion from mobility triggered by the UEs.
  • MBS Broadcast over NTN follows the Intended Service Area of a broadcast MBS session from the 5G Core to SIB27, the MCCH and the UE.
Sources for this page
  • Feeder link, service link, NTN payload, Mapped Cell ID: TS 38.300 V19.4.0, clauses 3.2 and 16.14.5.
  • Transparent and regenerative payload, cells and service links, Tracking Area, GNSS, FDD: TS 38.300 V19.4.0, clause 16.14.1.
  • Timing: TS 38.300 V19.4.0, clause 16.14.2.1.
  • Release context: TR 21.917 V17.0.1, clause 5.1.1; TR 21.918 V18.0.0, clause 5.1; TR 21.919 V19.0.0, clauses 5.1.1 and 5.4.1; TS 36.102 and TS 36.108 V19.5.0 and V20.0.0, clauses 5.2 and 5.3C (band 246); TS 22.261 V20.8.1, clause 6.46.2 and change history (CR 0835); TS 23.501 V20.3.0, clause 5.43.3 and change history (CR 6613).
  • MBS over NTN: TS 23.247 V20.0.0, clauses 4.1 and 6.21; TS 38.300 V19.4.0, clauses 16.10.1, 16.14.5 and 16.14.12; TS 38.331 V19.4.0, clause 6.3.1; TS 38.321 V17.15.0 and V19.4.0, clause 5.7. Release 18 comparison: TS 23.247 V18.8.0, TS 38.300 V18.11.0, TS 38.331 V18.11.0 and TS 38.413 V18.11.0 have no ISA or SIB27 text.

Related: Media delivery over 5G Multicast Broadcast Services · Media delivery over 5G Broadcast · Standards: Media delivery over 5G Multicast Broadcast Services · Standards: Media delivery over 5G Broadcast