By Joern Krause, 3GPP MCC 

Non-terrestrial networks (NTN) are networks or segments of networks that use either Uncrewed Aircraft Systems (UAS) operating typically between 8 and 50km altitudes, including High Altitude Platforms (HAPs) or satellites in different constellations to carry a transmission equipment relay node or a base station:

• LEO (Low Earth Orbit): Circular orbit in altitudes of typ. 500-2.000km (lower delay and better link budget but larger number of satellites needed for coverage)
• MEO (Medium Earth Orbit): Circular orbit in altitudes of typ. 8.000-20.000km
• GEO (Geostationary Earth Orbit): Circular orbit 35.786 km above the Earth's equator (Note: Due to gravitational forces a GEO satellite is still moving within a range of a few km around its nominal orbital position).
• HEO (Highly Elliptical Orbiting): Elliptical orbit around the earth.

Figure 1: Illustration of the classes of orbits of satellites [source: TR 22.822]

Two types of modes or "payload" can be distinguished, see also Figure 2:

• Non-regenerative payload (also called "bentpipe payload" (considering the path from the gateway via spaceborne/airborne platform to the UE) or "transparent mode"): A spaceborne/airborne platform with no on-board processing capabilities that changes the frequency carrier of the received uplink RF signal, filters and amplifies it before transmitting it on the downlink, i.e. the platform corresponds to an analogue RF repeater;

• Regenerative payload (or non-transparent mode): a spaceborne/airborne platform that has on top of RF filtering, frequency conversion and amplification also on-board processing capabilities (for demodulation/decoding, switching and/or routing, coding/modulation) so this spaceborne/airborne platform has base station functions on board.

Figure 2: Transparent vs. Regenerative payload and elliptic beam patterns [source: 38.811]

 

Figure 3: Illustration of elevation angle and propagation delay [source: TR 38.811]

Non-terrestrial networks (NTN) have a number of characteristics that require adaptations in comparison to terrestrial networks (TN) (see TR 38.811) including:

• Motion of the space/aerial vehicles: Only for GEO the satellite stays rather stable over the earth like in terrestrial networks. For LEO and MEO the satellites are moving with high velocity which leads to moving cell patterns, higher Doppler shifts/variations, faster propagation delay variations - requiring enhanced beam management (based on information about the predictable movement of the satellite (ephemeris) and the location/movement of the UE, the satellite network could know which beam and satellite covers the UE best).

As the moving cells may also cross country borders or cover areas with no territorial claims also regulatory aspects need to be taken into account (see TR 22.926).

• Altitude: Satellites operate in much higher altitudes than base stations of TNs which lead to longer latency (which needs to be taken into account in e.g. RACH, timing advance, HARQ, power control, MAC/RLC) due to larger propagation delays (TN: usually <1ms; GEO: up to a few 100ms) and it also impacts the link budget esp. in UL where the transmit power of the UE is limited.
• Cell sizes: NTN networks have larger cell sizes than TNs which could lead to higher variations of the propagation delays, stronger near far effects.
• Troposheric impacts: relevant above 6 GHz; like absorption, esp. relevant for higher frequencies (>10GHz) and low elevations (troposphere is the lower part of the atmosphere; below ~12km).
• Ionospheric impacts: relevant below 6GHz, reflection and absorption effects (also latitude dependency); (ionosphere is the upper part of the atmosphere; above ~80km; in which solar radiation creates layers of plasma due to ionisation).

Figures 4 and 5 show corresponding examples of Non-Terrestrial Network (NTN) architectures with a VSAT (Very Small Aperture Terminal) or a handheld/IoT device on the earth that communicates via a service link (also called user link) with a platform in the air or in space. This platform may communicate directly with a gateway on earth or at first via IAL (inter aerial link) or ISL (inter satellite link) via other platforms in the air or in space.

Instead of serving UEs directly via airborne/spaceborne platforms it is also possible that the Service link is arranged between an airborne/spaceborne platform and a relay node (using a VSAT) on the earth where the relay node then serves UEs. So the NTN Terminal would then be this relay node.

A VSAT has usually bigger dimensions and higher power than a handheld or IoT device serving as terminal or UE (user equipment).

If the airborne platform has the base station (gNB) on board (regenerative payload), then the NTN Gateway at the end of the feeder link can be a router to the Core network which connects to the public network.

In case of transparent/bent pipe payload the NTN Gateway at the end of the feeder link would be the base station (gNB) since the airborne platform operates just like a remote radio head relaying the signals.

The usage of inter-satellite links (ILS) requires regenerative payload.

In case of Non-Geostationary Satellite Orbit (NGSO), i.e. LEO or MEO, the spaceborne platform will move around the earth faster than the earth rotation which means that at some point in time the feeder link will need to change to another gateway and also that for service continuity the NTN terminal will need to be served by a different spaceborne platform. Regarding the beams from the satellite you can distinguish beams that move with the satellite (also called "moving beams") from steerable beams (i.e. by using e.g. beamforming techniques the satellite has the capability to steer a beams towards fixed points on earth (also called "earth fixed beam") for the time of the visibility of the satellite).

The feeder link between the NTN gateway and the satellite is also called Satellite Radio Interface (SRI).

 

Figure 4: Aerial access network (with IAL) with a service link operating
in frequency bands above 6 GHz [source: TR 38.811]

Figure 5: Satellite access network (with ISL) with a service link operating
in frequency bands above 6 GHz [source: TR 38.811]

NTN frequency bands:

In 3GPP, the NR bands in Table 1 (and the LTE bands in Table 2 see below) are/will be defined for NTN communication of the UE with the satellite.

Table 1: NR NTN satellite bands defined in 3GPP (see TS 38.101-5):

* Under discussion.

Pre-Release 15

3GPP standardization started with 3G in 1999 (Release 99) with a focus on terrestrial networks (T for terrestrial in UTRA). Also in 3GPP 4G standards the satellite aspects were limited to the support of location services via satellite (GPS, Galileo, GLONASS, BeiDou, NavIC ...).

In 3GPP Release 14 studies of use cases and requirements for 5G considered the extension of terrestrial networks via satellite and non-terrestrial networks. See

• radio requirements in TR 38.913
• system requirements for
  • critical communications in TR 22.862
  • enhanced mobile broadband in TR 22.864 and
  • 5G use cases in TR 22.891.

The main driving factors for considering non-terrestrial access were to:

• Allow for the provision of services for those areas where the terrestrial service is not available and also for those services that can be more efficiently supported via satellite, like multicasting/broadcasting of similar content over a large area ("service scalability").
• Provide better coverage in less densely populated/rural areas, on the sea, in high altitudes/airborne vehicles, in disaster zones where terrestrial networks could not operate reliably ("service ubiquity").
• Reduce vulnerability/higher resiliency of non-terrestrial networks.
• Reduce costs through a common radio interface for terrestrial and non-terrestrial networks via economies of scale and to provide service continuity.

Release 15

Release 15 was the first release that was standardizing normative requirements for 5G, initially focusing on the terrestrial network, with various architecture options.

Although stage 1 TS 22.261 of Release 15 added a 5G requirement regarding multiple access technologies: "The 5G system shall be able to support mobility between the supported access networks (e.g. NG-RAN, WLAN, fixed broadband access network, 5G satellite access network).",
time constraints meant that it was not yet possible to standardize satellite support in REL-15.

Nevertheless, a Release 15 Technical Specification Group (TSG) RAN led study item (SI) "Study on NR to support non-terrestrial networks" (FS_NR_nonterr_nw) with TR 38.811 was working on:

• Summarizing the use cases.
• Adapting the 3GPP channel model (developed in REL-14 TR 38.901 under the 5G REL-14 SI FS_NR_newRAT) for non-terrestrial networks.
• A detailed description of the deployment scenarios for non-terrestrial networks and corresponding analysis of necessary adaptations to support operation via Satellite or HAPS in NR.

Typical use cases of NTN networks are:

For enhanced Mobile Broadband (eMBB):

• NTN broadband connectivity to cells or relay nodes in underserved areas in combination with terrestrial wireless/cellular or wire line access featuring limited user throughput.
• NTN broadband connectivity between the core network and cells in un-served areas (isolated areas), also to restore connection to public data network in case of disaster relief or for public safety.
• NTN broadband connectivity between the core network and the cells on board a moving platform (e.g. aircraft or vessels or trains), including cases where NTN provides connectivity to a local terrestrial network on board of the moving platform.
• Network resilience: Secondary/backup connection to prevent complete connection outage for critical network links (although potentially limited in capability compared to the primary network connection).
• NTN to interconnect various 5G local access network islands not otherwise connected
• Broadcast/Multicast service via NTN e.g. to off load popular content from the terrestrial mobile network infrastructure.

For massive Machine Type Connection (mMTC):

• Global connectivity between IoT devices (sensors/actuators) and NTN network
• Connectivity to a base station serving IoT devices of a local area network

Release 15 TSG RAN study item FS_NR_nonterr_nw described the following deployment scenarios:

• GEO and Ka-band (higher GHz range) with VSAT relay as NTN node and transparent payload
• GEO and S-band (lower GHz range) with handheld UEs as NTN node and transparent payload
• LEO and S-band (lower GHz range) with handheld UEs as NTN node & regenerative payload
• LEO and Ka-band (higher GHz range) with VSAT relay as NTN node & regenerative payload
• HAPS in S- or Ka-band with handheld UEs as NTN node & regenerative payload

While D1./D4. look at indirect access via relay nodes, D2./D3. look at direct access of UEs.

Release 16

In Release 16 Non-Terrestrial Networks were addressed in 2 study items (SI):

On the systems side, the SA1 SI "Study on using Satellite Access in 5G" (FS_5GSAT) which resulted in TR 22.822. In this TR 12 more concrete use cases for NTN were analysed regarding conditions, impacts/interactions on existing services/features and potential

Stage 1 requirements:

• Roaming between terrestrial and satellite networks
• Broadcast and multicast with a satellite overlay
• Internet of Things with a satellite network
• Temporary use of a satellite component
• Optimal routing or steering over a satellite
• Satellite transborder service continuity
• Global satellite overlay
• Indirect connection through a 5G satellite access network
• 5G Fixed Backhaul between NR and the 5G Core
• 5G Moving Platform Backhaul
• 5G to Premises
• Satellite connection of remote service centre to off-shore wind farm

On the radio side, a Working Group (WG) RAN3 led SI "Study on solutions for NR to support non-terrestrial networks (NTN)" (FS_NR_NTN_solutions) (which was also covering WG RAN1 and WG RAN2 aspects) resulted in TR 38.821. Based on the key impacts of non-terrestrial networks (NTN) on NR identified in the REL-15 SI FS_NR_nonterr_nw, this REL-16 study item (SI) was studying impacts on RAN protocols/architecture in more detail and began to evaluate corresponding solutions.

The focus of this SI was on:

• Satellite access (with transparent GEO satellite and LEO based non-terrestrial access network (moving beam on earth), i.e. UAS/HAPS based access was considered here as a special case of NTN with lower Doppler and variation rate
• Usage scenarios: pedestrians or users on board of a vehicle (high speed train, airplane)

The considered reference scenarios were GEO, LEO with steering beams, LEO with moving beams and all for the transparent payload case and the regenerative payload case.

Figures 7 to 10 how the satellite access could be integrated in the 5G radio architecture in different scenarios:

Figure 7: Transparent satellite based NG-RAN architecture (gNB on earth) [source: TR 38.821]

In Fig.7 Control Plane (CP) and User Plane (UP) of NR Uu are terminated on the ground/on earth (longer round-trip time (RTT) needs to be taken into account).

Figure 8: Regenerative satellite based NG-RAN architecture without ISL (gNB on satellite)
[source: TR 38.821]

In Fig. 8 NR-Uu radio interface is on the service link between the UE and the satellite.

Figure 9: Regenerative satellite based NG-RAN architecture without ISL (gNBs on satellites)
[source: TR 38.821]

In Fig. 9 a UE (served by a gNB on board a satellite) could access the 5GCN also via ISL which is a transport link between satellites. So not necessarily 2 connections to the data network are needed.

Figure 10: Regenerative satellite based NG-RAN architecture without ISL (gNB-DU on satellite and gNB-CU on earth) [source: TR 38.821]

Fig. 10 illustrates how a split of the gNB functionality into CU (central unit) and DU (distributed unit) would look like. The feeder link/SRI between NTN gateway and satellite would then transport the F1 protocol. As RRC and other Layer3 processing are terminated in the gNB-CU on ground corresponding timing impacts are the consequence (worse for GEO than for LEO). It would be possible that the DU on board different satellites is connected to the same CU on ground.

Apart from NTN-TN service continuity scenarios also multi-connectivity scenarios were considered in which one UE is served:

• In parallel by an NTN (transparent or regnerative payload) and a terrestrial network (TN)
• In paralle by 2 NTNs (both transparent or both with regenerative payload)

(with at least partial coverage overlap) in order to improve performance (like data rate or reliability) in certain scenarios.

For WG RAN1, the study resulted in the proposals to focus the normative work on:

• Timing relationship enhancements
• Enhancements on UL time and frequency synchronization
• Enhancement on the PRACH sequence and/or format in the case pre-compensation of    timing and frequency offset is not done at UE side
• Beam management and BWP operation for NTN with frequency reuse including signalling of         polarization mode
• Feeder link switch impact on physical layer procedures in case of LEO scenarios
• Number of HARQ processes, support of enabling / disabling of HARQ feedback.

WG RAN2 concluded that NR can support NTN scenarios with the following recommendations /enhancement ideas for the normative phase:

• Offset based solutions for timer adaptations are preferred, earth fixed tracking area is recommended
• MAC enhancements (for random access, timing advance, DRX, Scheduling Request, HARQ)
• RLC enhancements (for status reporting, sequence numbers)
• PDCP enhancements (SDU discard, sequence numbers)
• Idle mode enhancements: additional assistance information for cell selection/reselection (e.g. UE location, satellite Ephemeris information), earth-fixed tracking area to avoid frequent TAU, NTN cell specific information in SIB.
• Connected mode enhancements: reduce service interruption during Hand-Over due to large        propagation delay, tackle frequent handover and high handover rate due to satellite movement, improve handover robustness due to small signal strength variation in regions of beam overlap, compensate for propagation delay differences in the UE measurement window between cells originating from different satellites.
• Other mobility enhancements: additional CHO triggering conditions, enhancements to   mobility configuration , measurement configuration/reporting, service continuity TN to NTNand NTN to TN.
• RACH procedure: inclusion of assistance information with trade-off between latency gain and UL overhead.

WG RAN3 suggested to focus normative work on:

• GEO based satellite access with transparent payloads
• LEO based satellite access with transparent or regenerative payloads

Release 17

Release 17 (ASN.1 frozen in June 2022) was the first release with normative requirements for NTN in 3GPP specifications.

WG SA1

Release 17 WI "Stage 1 of 5GSAT" (5GSAT) transformed the results of the Release 16 SI FS_5GSAT into stage 1 requirements in TS 22.261 (see also SP-200569 CR0428rev4). Note: TS 22.261 is the stage 1 description of the 5G system and this TS exists therefore since Release 15. There are requirements like:

• The 5G system shall support service continuity between 5G terrestrial access network and 5G satellite access networks owned by the same operator or owned by different operators having an agreement (clause 6.2.3).
• A 5G system with satellite access shall enable roaming of UE supporting both satellite access and terrestrial access between 5G satellite networks and 5G terrestrial networks (clause 6.2.4).
• UEs supporting satellite access shall support optimized network selection and reselection to PLMNs with satellite access, based on home operator policy (clause 6.2.4).
• The 5G system shall be able to support mobility between the supported access networks (e.g. NG-RAN, WLAN, fixed broadband access network, 5G satellite access network) (clause 6.3.2.1).
• The 5G system shall be able to provide services using satellite access (clause 6.3.2.3).
• A 5G system with satellite access shall support different configurations where the radio access network is either a satellite NG-RAN or a non-3GPP satellite access network, or both (clause 6.3.2.3).
• A UE supporting satellite access shall be able to provide or assist in providing its location to the 5G network (clause 6.3.2.3).
• A 5G system with satellite access shall be able to determine a UE's location in order to provide service (e.g. route traffic, support emergency calls) in accordance with the governing national or regional regulatory requirements applicable to that UE (clause 6.3.2.3).
• The 5G system with satellite access shall be able to support low power MIoT type of communications (clause 6.3.2.3).
• The 5G system with satellite access shall support the use of satellite links between the radio access network and core network, by enhancing the 3GPP system to handle the latencies introduced by satellite backhaul (clause 6.4.2.1).
• A 5G system with satellite access shall be able to support meshed connectivity between satellites interconnected with intersatellite links (clause 6.4.2.1).
• A 5G system with satellite access shall be able to select the communication link providing the UE with the connectivity that most closely fulfils the agreed QoS (clause 6.5.2).
• A 5G system with satellite access shall be capable of supporting simultaneous use of 5G satellite access network and 5G terrestrial access networks (clause 6.5.2).
• A 5G system with satellite access shall be able to support both UEs supporting only satellite access and UEs supporting simultaneous connectivity to 5G satellite access network and 5G terrestrial access network (clause 6.5.2).
• A 5G system with satellite access shall be able to optimise the delivery of content from a content caching application by taking advantage of satellites in supporting ubiquitous service, as well as broadcasting/multicasting on very large to global coverages (clause 6.6.2).
• A 5G system with satellite access shall be able to support relay UE's with satellite access (clause 6.9.2.5).
• A 5G system with satellite access shall support mobility management of relay UEs and the remote UEs connected to the relay UE between a 5G satellite access network and a 5G terrestrial network, and between 5G satellite access networks (clause 6.9.2.5).
• A 5G system with satellite access shall support joint roaming between different 5G networks of a relay UE and the remote UEs connected to that relay UE (clause 6.9.2.5).
• The 5G system shall support multicast/broadcast via a 5G satellite access network, or via a combination of a 5G satellite access network and other 5G access networks (clause 6.13.2).
• A 5G satellite access network shall support NG-RAN sharing (clause 6.21.2).
• The 5G system shall support mechanisms to determine the UE’s position-related data for period when the UE is outside the coverage of 3GPP RAT-dependent positioning technologies but within the 5G positioning service area (e.g. within the coverage of satellite access) (clause 6.27.2).
• A 5G satellite access network connected to 5G core networks in multiple countries shall be able to meet the corresponding regulatory requirements from these countries (e.g. Lawful Interception) (clause 8.6).
• The 5G core network shall support collection of charging information based on the access type (e.g. 3GPP, non-3GPP, satellite access) (clause 9.1).
• In a 5G system with satellite access, charging call records associated with satellite access(es) shall include the location of the associated UE(s) with satellite access (clause 9.1).

WG SA2

Release 17 SI "Study on architecture aspects for using satellite access in 5G" (FS_5GSAT_ARCH) resulted in TR 23.737. It was identifying 10 key issues for 2 reference use cases:

1. Roaming between terrestrial and satellite networks – to cover the direct satellite access.
2. 5G Fixed Backhaul between NR and the 5G Core – to cover the satellite backhaul.

The issues:

• Mobility management with large satellite coverage areas
• Mobility Management with moving satellite coverage areas
• Delay in satellite
• QoS with satellite access
• QoS with satellite backhaul
• RAN mobility with NGSO regenerative-based satellite access
• Multi connectivity with satellite access *
• The role of satellite link in content distribution towards the edge *
• Multi connectivity with hybrid satellite/terrestrial backhaul *
• Regulatory services with super-national satellite ground station

14 solutions were proposed (which could address multiple key issues) and corresponding evaluations of the solutions were provided with suggested way forwards on the key issues (e.g. no normative work is planned for the key issues with * above).

Based on the results of SI FS_5GSAT_ARCH, the corresponding Release 17 normative stage 2 work happened in the SA2 Release 17 WI "Stage 2 of Integration of satellite components in the 5G architecture" (5GSAT_ARCH). The results were captured in 3 existing stage 2 specifications:

• TS 23.501 "System architecture for the 5G System (5GS); Stage 2"
• TS 23.502 "Procedures for the 5G System (5GS); Stage 2"
• TS 23.503 "Policy and charging control framework for the 5G System (5GS); Stage 2" under the following assumptions for Release 17:
• focus on transparent payload based LEO and GEO scenarios
• UEs are assumed to have the capability to determine their location
• Earth fixed Tracking Areas (TA) deployment will be supported to minimise 5GCN impact

The related stage 3 work from CT WGs was carried out in REL-17 WI 5GSAT_ARCH-CT. It included also a TR 24.821 studying the PLMN selection for satellite access.

WG SA5

In SA5 there was a Release 17 SI "Study on management and orchestration aspects with integrated satellite components in a 5G network" (FS_5GSAT_MO) which resulted in TR 28.808 analyzing

• Reference management architectures for integrated satellite components
• Use cases, potential requirements & solutions
  • related to network slice management
  • for the management of satellite components
  • for monitoring of satellite components

and recommending the following aspects for normative work:

• Specify/extend SON concepts to allow for moving non-terrestrial gNBs
• Adapt the performance measurements which make use of the HARQ process, which may be unavailable when using satellite RAN
• Extend the 5G Network Resource Model (NRM) to support satellite components, for example by adding ServiceProfile attributes
• Specify the approach to use load balancing between terrestrial RAN and non-terrestrial RAN to guarantee service continuity and reliability

TSG RAN

On the radio side the TSG RAN Release 17 WI Solutions for NR to support non-terrestrial networks (NTN) (NR_NTN_solutions) was carried out under the following assumptions:

• Only transparent payload
• Operating band using FDD in frequency range FR1 (i.e. 410MHz - 7125MHz); resulting in 2 new bands n255 (L-band) and n256 (S-band) in TS 38.101-5/TS 38.108
• Handheld devices with power class 3 are supported
• UEs with GNSS capabilities are assumed
• Earth-fixed tracking areas with earth fixed or moving cells (see TR 38.821 clause 7.3.1.3; TS23.501 clause 5.4.11.7)

For HAPS operation it was concluded:

• NR operating band n1 (FDD: UL: 1920 - 1980MHz, DL 2110 - 2170MHz) can be applied
• Wide Area BS class is applicable as in TS 38.104 without additional changes
• NR UEs as defined by TS 38.101-1 can support HAPS deployments with no additional changes.

Timing, Synchronization and HARQ enhancements (WG RAN1)

The network broadcasts ephemeris information and common Timing Advance (common TA) parameters in each NTN cell. Since NTN capable UEs are expected to be all GNSS-capable, they shall acquire a valid GNSS position as well as the satellite ephemeris and common TA before connecting to an NTN cell.

To achieve uplink synchronisation, before performing random access, the UE shall autonomously pre-compensate the Timing Advance, as well as the frequency Doppler shift by considering the common TA (information from the gNB), the UE position, the satellite position and satellite velocity through the satellite ephemeris. In connected mode, the UE shall continuously update the Timing Advance and frequency pre-compensation. If the UE does not have a valid GNSS position and/or valid satellite ephemeris, it does not communicate with the network until both are regained. The UEs may be configured to report Timing Advance at initial access or in connected mode. In connected mode triggered reporting of the Timing Advance is supported.

While the pre-compensation of the instantaneous Doppler shift experienced on the service link is to be performed by the UE for the uplink, the management of Doppler shift experienced over the feeder link is left to the network implementation.

To accommodate the propagation delay in NTNs, several timing relationships are enhanced by a Common Timing Advance (Common TA) and two scheduling offsets K_offset and k_mac. Common TA is a configured offset that corresponds to the Round Trip Time (RTT) between the Reference Point (RP) and the NTN payload. K_offset is a configured scheduling offset that approximately corresponds to the sum of the service link RTT and the common TA. k_mac is a configured offset that approximately corresponds to the RTT between the Reference Point (RP) and the gNB.

To mitigate the impact of HARQ stalling in NTN, the HARQ feedback can be disabled in the presence of ARQ re-transmissions at the RLC layer (e.g., in GSO satellite systems) and/or the number of HARQ processes for re-transmissions at the MAC layer can be increased to 32 (e.g., in NGSO satellite systems).

Mobility Management (WG RAN2)

To enable mobility in NTN, the network provides serving cell's and neighbouring cell's satellite ephemeris needed to access the target serving NTN cell in the handover command.

UE supports mobility between NTN and Terrestrial Network (i.e. from NTN to Terrestrial Network (hand-in) and from Terrestrial Network to NTN (hand-out)), but is not required to connect to both NTN and Terrestrial Network at the same time. It may also support mobility between radio access technologies based on different orbit (GSO, NGSO at different altitude).

Triggering conditions upon which a UE may execute Conditional Hand-Over (CHO) to a candidate cell, have been introduced: event A4, time-based trigger condition, location-based trigger condition. The two last conditions are configured together with one of the measurement-based trigger conditions. Location is defined by the distance between UE and a reference location. Time is defined by the time between T1 and T2, where T1 is an absolute time value and T2 is a duration started at T1.

For the measurements the network can configure multiple SS/PBCH Block Measurement Timing Configuration (SMTCs) in parallel per carrier and for a given set of cells depending on UE capabilities using propagation delay difference and ephemeris information. It can also configure measurement gaps based on multiple SMTC.

The adjustment of SMTCs is possible: Under network control based on UE assistance information if available for connected mode and under UE control based on UE location and satellite assistance information (e.g.,    ephemeris, common TA parameters) for idle/inactive modes.

In the quasi-earth fixed cell scenario, UE can perform time-based and location-based measurement in RRC_IDLE/RRC_INACTIVE. The timing and location information associated to a cell are provided via system information. They refer respectively to the time when the serving cell is going to stop serving a geographical area and to the reference location of serving cell.

A Tracking Area corresponds to a fixed geographical area. Any respective mapping is configured in the RAN. The network may broadcast multiple Tracking Area Codes (TAC) per PLMN in a NR NTN cell in order to reduce the signalling load at cell edge, in particular for Earth-moving cell coverage. A TAC change in the System Information is under network control and may not be exactly synchronised with real-time illumination of beams on ground.

Regarding the UE location aspects, upon network request, after AS security is established in connected mode, a UE should report its coarse UE location information (most significant bits of the GNSS coordinates, ensuring an accuracy in the order of 2 km) to the NG-RAN if available.

Switch-over (WG RAN3):

A service link switch refers to a change of serving satellite.

A feeder link switch over is the procedure where the feeder link is changed from a source NTN Gateway to a target NTN Gateway for a specific NTN payload. The feeder link switch over is a Transport Network Layer procedure. Both hard and soft feeder link switch over are applicable to NTN. Service and feeder link switch overs apply mostly for the case of NGSO.

NG-RAN signalling (WG RAN3):

The Cell Identity, indicated by the gNB to the Core Network as part of the User Location Information corresponds to a Mapped Cell ID, irrespective of the orbit of the NTN payload or the types of service links supported. It is used for Paging Optimization in NG interface, Area of Interest and Public Warning Services.

The Cell Identity included within the target identification of the handover messages allows identifying the correct target radio cell as well as for RAN paging.

The mapping between Mapped Cell IDs and geographical areas is configured in the RAN and Core Network. The gNB is responsible for constructing the Mapped Cell ID based on the UE location info received from the UE, if available. The mapping may be pre-configured (e.g., up to operator's policy) or up to implementation.

The gNB reports the broadcasted TAC(s) of the selected Public Land Mobile Network (PLMN) to the Access and Mobility Management Function (AMF) as part of UE Location Information (ULI). In case the gNB knows the UE's location information, the gNB may determine the Tracking Area Indicator (TAI) the UE is currently located in and provide that TAI to the AMF as part of ULI.

AMF (Re-)Selection by gNB (WG RAN3):

For a RRC_CONNECTED UE, when the gNB is configured to ensure that the UE connects to an AMF that serves the country in which the UE is located. If the gNB detects that the UE is in a different country to that served by the serving AMF, then it should perform an NG handover to change to an appropriate AMF, or initiate an UE Context Release Request procedure towards the serving AMF (in which case the AMF may decide to de-register the UE).

O&M Requirements (WG RAN3):

• The NTN related parameters (see clause 16.14.7 of TS 38.300):
• Ephemeris information (2 formats possible) describing the orbital trajectory information or coordinates for the NTN payload
• The explicit epoch time associated to ephemeris data
• The location of the NTN Gateways
• Additional information to enable gNB operation for feeder/service link switch overs shall be provided by O&M to the gNB providing non-terrestrial access. Additional NTN related parameters may be provided by O&M to the gNB for its operation (see Annex B4 of TS 38.300 for examples).

RF performances and RRM requirements (WG RAN4)

Based on coexistence studies captured in TR 38.863, the minimum RF and performance requirements in FR1 for respectively NR User Equipment (UE) supporting satellite access operation and NR Satellite Access Node (SAN) were defined in TS 38.101-5 and TS 38.108.

WG RAN5 Release 17 WI "UE Conformance - Solutions for NR to support non-terrestrial networks (NTN) plus CT aspects" (NR_NTN_solutions_plus_CT-UEConTest) is carrying out the UE testing of functionality introduced by Release 17 RAN2 led WI NR_NTN_solutions-Core and Release 17 CT WI 5GSAT_ARCH-CT.

Release 18

The TSG RAN Release 18 SI "Study on self-evaluation towards the IMT-2020 submission of the 3GPP Satellite Radio Interface Technology" (FS_IMT2020_SAT_eval) is evaluating the REL-17 functionaltity of NR based WI NR_NTN_solutions to support 5G via satellite together with the LTE based work that happened to support IoT via NTN (i.e. Release 17 WI LTE_NBIOT_eMTC_NTN-Core covering RAN1/2/3 aspects and Release 18 WI LTE_NBIOT_eMTC_NTN_req which covered the missing RAN4 aspects).

3GPP has two submissions for the satellite component of IMT-2020 to ITU-R WP4B:

Submission 1 (SRIT: set of radio interface technologies) with 2 components:

• • Component RIT: NR NTN (NR satellite access)
  • Component RIT: IoT NTN (NB-IoT/eMTC satellite access)

Submission 2 (RIT: radio interface technology):

• • NR NTN (NR satellite access)

Three different usage scenarios are analyzed in a rural environment:

• eMBB-s (Enhanced Mobile Broadband - satellite)
• HRC-s (High Reliability Communications - satellite)
• mMTC-s (Massive machine type communications – satellite)

The results of this SI are captured in TR 37.911 and the goal is to verify that the 3GPP solutions meet the requirements defined by ITU in Report ITU-R M.2514 qualifying for the ITU-Recommendation specifying the satellite component of IMT-2020.

WG RAN4 Release 18 WI "30 MHz Channel Bandwidth for NR NTN (non-terrestrial networks) in FR1 (frequency range 1)" (NR_NTN_CBW_30MHz-Core) was adding the channel bandwidth of 30MHz to the already supported channel bandwidths of 5MHz, 10MHz, 15MHz and 20MHz for the operating bands n255 (L-band) and n256 (S-band) for the Satellit Access Node (SAN) and the UE and added corresponding requirements.

This work was triggered by the fact that requirements and evaluation guidelines for satellite radio interface(s) of IMT-2020 in ITU have assumed a maximum channel bandwidth of 30 MHz and so 3GPP aligned corresponding RAN4 specifications TS 38.101-5 (for the UE) and TS 38.108 (for the SAN).

The TSG RAN Release 18 SI "Study on requirements and use cases for network verified UE location for Non-Terrestrial-Networks (NTN) in NR" (FS_NR_NTN_netw_verif_UE_loc) resulted in TR 38.882:

With NTN it is possible to deploy very large cells over large portions of a continent (possibly covering different countries), with the different core networks for the various countries connected to the same NTN RAN where the serving cell information may not be granular enough to know a UE's location following national or regional regulatory requirements (e.g. for public warning systems, emergency call support, legal interception).

So this SI concluded on the need for a network based solution which aims at verifying the reported UE location information (within 5-10km, like the diameter of a terrestrial macro cell) and corresponding normative work is supposed to happen under the Release 18 WI NR_NTN_enh.

WG SA2

The Release 18 "Study on 5GC enhancement for satellite access Phase 2" (FS_5GSAT_Ph2) was looking at mobility management and power savings in case of discontinuous coverage (i.e. a UE may have access to satellite service coverage only at specific time and places) and resulted in TR 23.700-28. Dynamic support of discontinuous coverage is required for initial NGSO constellation deployment but as well to support evolution of the constellations such as loss of satellites, different releases supported in a given constellation. So this SI looked into mobility management, paging enhancements, UE power savings, procedures to determine and coordinate the UE unreachability period.

Corresponding normative stage 2 work happened in Release 18 "Stage 2 of 5GSAT_Ph2: 5GC/EPC enhancement for satellite access Phase 2" (5GSAT_Ph2) and stage 3 work was done in WGs CT1/CT6 Release 18 WI "CTx aspects of 5GSAT_Ph2" (5GSAT_Ph2) including also the handling of signalling overload due to loss of coverage and return to coverage of many UEs at the same time.

WG SA3

Release 18 SI "Study on Security Aspects of Satellite Access" (FS_5GSAT_Sec) was looking at security/privacy issues for mobility management and power savings in case of discontinuous coverage and identified only one issue in TR 33.700-28: satellite coverage availability information could be received by 5GC/EPC from different potential sources, e.g. the OAM, the AF/external server (e.g. Coverage Map Server). While the sources like the OAM could be trusted, the sources like the AF/external server may not always be trusted.

It concluded that satellite coverage information is provisioned to the AMF by O&M only. Hence no normative work is needed on AF authorization.

WG RAN4

Release 18 WI "Introduction of the satellite L-/S-band for NR" (NR_NTN_LSband) was specifying a new FDD NTN band (called band n254) on top of the bands n255 (L-band) and n256 (S-band) that were introduced in Release 17 WI NR_NTN_solutions: For band n254 the UE is transmitting at 1610-1626.5MHz (UL, L-band) and the Satellite Access Node (SAN) is transmitting at 2483.5-2500MHz (DL, S-band).

The WG RAN2 led Release 18 WI "NR NTN (Non-Terrestrial Networks) enhancements" (NR_NTN_enh) had the goal to enhance NTN related features introduced in earlier releases (esp. REL-17):

• Coverage enhancement: To improve NR uplink coverage in NTN: PUCCH repetition for Msg4 HARQ-ACK; PUSCH DMRS bundling enhancement so that UE can maintain phase continuity in case of timing drift.
• Network verified UE location (compare REL-18 SI FS_NR_NTN_netw_verif_UE_loc): some UE and gNB Rx/Tx time measurements are defined in order to allow verification of the UE location
• NTN-TN and NTN-NTN mobility and service continuity enhancements: e.g. SIB19 in TN to include NTN-specific parameters for NTN neighbour cells; to improve NTN-TN mobility the SAN may broadcast in a system information block a list of geographical TN areas with associated frequency information; improved trigger conditions (time-based/location based) for conditional handover; satellite switch with re-sync
• NR-NTN deployment in above 10 GHz bands: e.g. new bands n510, n511, n512 in 20-30GHz range (Ka-band) will be introduced; Rx/Tx requirements for selected VSAT UE class/types and SAN for the Ka band; RRM for electronically-steered beam UEs (type 1) and mechanically-steered beam UEs (type 2).

The WG SA2 Release 18 SI "Study on Support of Satellite Backhauling in 5GS" (FS_5GSATB) is looking at satellite based backhaul which is important for remote area or mission critical scenarios, in case it is not possible to build terrestrial backhaul connections. It discussed solutions for 3 key issues and captured the results in TR 23.700-27:

• Dynamic satellite backhaul i.e. problems in case of multi-hops of ISL or backhaul connections are over different satellites and terrestrial networks like packet delivery latency, bandwidth of the backhaul, packets out-of-sequence.
• Satellite Edge Computing via UPF on board of the satellite to to reduce latency and minimize the backhaul resources consumption.
• Local Data Switching via UPF on-board of the satellite to reduce end to end delay for UEs in a communication

The WG SA1 Release 18 WI "Stage 1 of 5GSATB (Satellite Backhauling in 5GS)" (5GSATB) added requirements for QoS control and charging when using satellites as transport/backhaul in 5G system to the existing TS 22.261.

A corresponding WG SA2 Release 18 WI "Stage 2 of 5GSATB (Satellite Backhauling in 5GS)" (5GSATB) was covering the results of Release 18 SI FS_5GSATB in existing TS 23.501 (architectural enhancements), TS 23.502 (procedural enhancements)and TS 23.503 (policy enhancements).

The stage 3 aspects were then addressed in the WGs CT3/CT4 Release 18 WI "CTx aspects of 5GSATB (Satellite Backhauling in 5GS)" (5GSATB).

WG SA5 Release 18 SI "Study on charging aspects of Satellite in 5GS" (FS_5GSAT_CH) studied in TR 28.844 aspects of:

• Satellite access charging
• Satellite backhaul charging
• Subscriber and inter-provider charging for Edge Computing with satellite backhaul
• Charging for SSC-to-SSC (Satellite Service Customer) communications via satellite in case of local data switching (via UPF(s) deployed on satellite)

Corresponding normative work was carried out:

• For satellite access charging: in SA5 Release 18 WI "Charging aspects of 5GSAT" (5GSAT_Ph2_CH)
• For the other 3 bullets (satellite backhaul charging etc.): in WG SA5 Release 18 WI "Charging aspects of Satellite Backhaul in 5GS" (5GSATB_Ph2_CH).

Release 19

The Release 19 WG RAN2 led WI "Non-Terrestrial Networks (NTN) for Internet of Things (IoT) Phase 3" (NR_NTN_Ph3) has the following objectives which will be considered in 2024/2025:

• DL coverage enhancements targeting support for additional reference satellite payload parameters covering both GSO and NGSO constellations operating in FR1-NTN or FR2-NTN
• Uplink capacity/throughput enhancement for FR1-NTN
• Signaling of the intended service area of a broadcast service (e.g. MBS broadcast) via NR NTN
• Support of regenerative payload (i.e. 5G system functions on board the NTN vehicle)
• Support RedCap UEs with NR NTN operating in FR1-NTN bands

WG SA1 Release 19 SI "Study on satellite access - Phase 3" (FS_5GSAT_Ph3) studies use cases and requirements for further enhancements of the 5G system over satellite (see TR 22.865):

• Store and Forward (S&F) Satellite operation for delay-tolerant communication service: to provide communication service for UEs under satellite coverage without a simultaneous active feeder link connection to the ground segment (esp. relevant for delay-tolerant IoT services via NGSO space segment).
• UE-Satellite-UE communication: In some scenarios, UEs need to communicate using satellite access without going to the ground network in order to avoid long delays and limited data rate as well as reducing the consumption of backhaul resources.(Note: REL-17 and REL-18 assumed transparent mode for the satellite access.)
• GNSS independent operation: to provide satellite access to UEs without GNSS receiver or with no access to GNSS services (note: For REL-17 and REL-18 only GNSS capable UEs are supported.)
• Positioning enhancements for satellite access: 3GPP positioning methods are needed in some scenarios for UEs using only satellite access.

Corresponding normative stage 1 requirements were captured in TS 22.261 in WG SA1 Release 19 WI "Satellite access Phase 3" (5GSAT_Ph3).

WG SA2 Release 19 SI "Study on Integration of satellite components in the 5G architecture Phase 3" (FS_5GSAT_ARCH_Ph3) is based on the WG SA1 SI and will study:

• Regenerative payload generic architecture
• Store and Forward satellite operation
• UE-satellite-UE communication enhancements for 5GS, supporting NR NTN NGSO constellation with and without ISL, with feeder link available (at least for session establishment)

Results will be documented in TR 23.700-29.

WG SA3 Release 19 SI "Study on Security Aspects of 5G Satellite Access Phase 2" (FS_5GSAT_SEC_Ph2) will study security and privacy key issues of:

• Regenerative payload in 5GS & EPS
• Store and Forward satellite operation for NR NTN (5GS) and IoT NTN (EPS)
• UE-satellite-UE communication enhancements for 5GS

Results will be documented in TR 33.700-29.

WG SA5 Release 19 SI "Study on Management Aspects of NTN Phase 2" (FS_NTN_OAM_Ph2) will study the following aspects:

• Management capabilities to support new network architecture or functions for satellite regenerative payloads, considering different types of satellite constellations (both GSO and NGSO).
• Management requirement, usecase and solution to support Store and Forward (S&F) satellite operation and UE-Satellite-UE communication.
• Requirements and potential solutions to support end to end management (including RAN domain and CN domain) in NTN scenarios, such as coordinate with non-3GPP part (e.g. Satellite Control System, Transport System) to provide the NTN specific requirements.
• Management enhancement for NTN-TN and NTN-NTN mobility coordination and better service continuity.

Results will be documented in TR 28.874.

WG SA6 Release 19 SI "Study on application enablement for Satellite access enabled 5G Services" (FS_5GSAT_APP) will study:

• Application layer solutions for satellite access: using satellite access characteristics, supporting predictable discontinuous /intermittent connectivity patterns between UEs and AS/AFs for IoT services with satellite access, supporting delivery of content from a content caching application
• Usage of satellite communication for Mission Critical services (to provide better user experience, identify key issues, deployment models and develop solutions)

Results will be documented in TR 23.700-01.

Radio related SIs/WIs for NTN:

REL	Acronym	led by	Title	description	status report	start	end	further documentation/infos
REL-15	FS_NR_nonterr_nw	RAN	Study on NR to support non-terrestrial networks	RP-171450	RP-181293	March 17	June 18	TR 38.811
REL-16	FS_NR_NTN_solutions	RAN3	Study on solutions for NR to support non-terrestrial networks (NTN)	RP-190710	RP-192410	June 18	Dec.19	TR 38.821
REL-17	NR_NTN_solutions	RAN2	Solutions for NR to support non-terrestrial networks (NTN)	RP-222556	RP-221745, RP-230115	Dec.19	Core: June 22 Perf.: March 23	RP-221946; TR 38.863, TS 38.108, TS 38.101-5, TS 38.181
REL-17	NR_NTN_solutions_plus_CT-UEConTest	RAN5	UE Conformance - Solutions for NR to support non-terrestrial networks (NTN) plus CT aspects	RP-233929	RP-233922	June 22	June 24	tested: REL-17 WI NR_NTN_solutions-Core and CT REL-17 WI 5GSAT_ARCH-CT; TS 38.521-5
REL-18	FS_IMT2020_SAT_eval	RAN	Study on self-evaluation towards the IMT-2020 submission of the 3GPP Satellite Radio Interface Technology	RP-231296	RP-233868	March 23	Dec.23	TR 37.911 evaluating REL-17 WIs NR_NTN_solutions and LTE_NBIOT_eMTC_NTN-Core for IMT-2020 submission to ITU-R
REL-18	FS_NR_NTN_netw_verif_UE_loc	RAN	Study on requirements and use cases for network verified UE location for Non-Terrestrial-Networks (NTN) in NR	RP-221820	-	June 22	June 22	TR 38.882
REL-18	NR_NTN_enh	RAN2	NR NTN (Non-Terrestrial Networks) enhancements	RP-234011	RP-232858	Dec.21	Core: March 24 Perf.: June 24
REL-18	NR_NTN_CBW_30MHz-Core	RAN4	30 MHz Channel Bandwidth for NR NTN (non-terrestrial networks) in FR1 (frequency range 1)	RP-232647	RP-232646	June 23	Sep.23	no Perf. part; REL-independent approach (i.e. from REL-17)
REL-18	NR_NTN_LSband	RAN4	Introduction of the satellite L-/S-band for NR	RP-234043	RP-233306	Dec.22	Core: Dec.23 Perf.: Dec.23	UL: 1610-1626.5MHz; DL: 2483.5-2500MHz; TR 38.741
REL-19	NR_NTN_Ph3	RAN2	Non-Terrestrial Networks (NTN) for NR Phase 3	RP-234078	-	Dec.23	Core: Sep.25 Perf.: March 26

Systems/Core Network related SIs/WIs for NTN:

 

REL	Acronym	led by	Title	description	of TSG#	start	end	further documentation/infos
REL-16	FS_5GSAT	SA1	Study on using Satellite Access in 5G	SP-170702	77	Sep.17	June 18	TR 22.822
REL-17	5GSAT	SA1	Stage 1 of 5GSAT	SP-180326	80	June 18	Sep.18	TS 22.261; was originally a REL-16 WI which was shifted to REL-17
REL-17	FS_5GSAT_ARCH	SA2	Study on architecture aspects for using satellite access in 5G	SP-181253	82	June 18	June 20	TR 23.737
REL-17	5GSAT_ARCH	SA2	Stage 2 of Integration of satellite components in the 5G architecture	SP-191335	86	Dec.19	Sep.21	TS 23.501; TS 23.502; TS 23.503
REL-17	5GSAT_ARCH-CT	CTx	CTx aspects of 5GC architecture for satellite networks	CP-210149	91e	Sep.20	March 22	TR 24.821, TS 23.122; TS 24.501; TS 24.008, TS 24.301, TS 29.571, TS 29.512, TS 31.102
REL-17	FS_5GSAT_MO	SA5	Study on management and orchestration aspects with integrated satellite components in a 5G network	SP-190138	83	March 19	March 21	TR 28.808
REL-18	FS_5GSAT_Ph2	SA2	Study on 5GC enhancement for satellite access Phase 2	SP-211651	94e	Dec.21	Dec.22	TR 23.700-28
REL-18	FS_5GSAT_Sec	SA3	Study on Security Aspects of Satellite Access	SP-220875	97e	Sep.22	March 23	TR 33.700-28
REL-18	5GSAT_Ph2	SA2	Stage 2 of 5GSAT_Ph2: 5GC/EPC enhancement for satellite access Phase 2	SP-230109	99	Dec.22	June 23	TS 23.501, TS 23.502, TS 23.503, TS 23.401
REL-18	5GSAT_Ph2	CTx	CTx aspects of 5GSAT_Ph2	CP-232167	101	March 23	March 24	TS 24.501, TS 24.301, TS 23.122, TS 27.007, TS 29.122, TS 29.522, TS 31.102
REL-18	5GSATB	SA1	Stage 1 of 5GSATB	SP-210528	92e	June 21	June 21	TR 22.261
REL-18	FS_5GSATB	SA2	Study on Support of Satellite Backhauling in 5GS	SP-211639	94e	Dec.21	March 23	TR 23.700-27
REL-18	5GSATB	SA2	Stage 2 of 5GSATB	SP-230111	99	Sep.22	June 23	TS 23.501, TS 23.502, TS 23.503
REL-18	5GSATB	CTx	CTx aspects of 5GSATB	CP-232131	101	Dec.22	Dec.23	TS 29.512, TS 29.514, TS 29.522, TS 29.525, TS 29.513, TS 29.502, TS 29.244, TS 29.564
REL-18	FS_5GSAT_CH	SA5	Study on charging aspects of Satellite in 5GS	SP-221162	98e	June 22	Dec.23	TR 28.844
REL-18	5GSAT_Ph2_CH	SA5	Charging aspects of 5GSAT	SP-231152	101	Sep.23	March 24	TS 32.255; TS 32.256; TS 32.291; TS 32.298
REL-18	5GSATB_Ph2_CH	SA5	Charging aspects of Satellite Backhaul in 5GS	SP-231435	102	Dec.23	March 24	TS 32.240, TS 32.255, TS 32.256, TS 32.254, TS 32.257, TS 32.291, TS 32.298
REL-19	FS_5GSAT_Ph3	SA1	Study on satellite access - Phase 3	SP-220679	96	June 22	Sep.23	TR 22.865
REL-19	5GSAT_Ph3	SA1	Satellite access Phase 3	SP-230516	100	June 23	Dec.23	TS 22.261
REL-19	FS_5GSAT_ARCH_Ph3	SA2	Study on Integration of satellite components in the 5G architecture Phase 3	SP-231199	101	Sep.23	June 24	TR 23.700-29
REL-19	FS_5GSAT_SEC_Ph2 or FS_5GSAT_SEC_Ph3	SA3	Study on Security Aspects of 5G Satellite Access Phase 2	SP-231790	102	Dec.23	Dec. 24	TR 33.700-29
REL-19	FS_NTN_MGT_ph2 or FS_NTN_OAM_Ph2	SA5	Study on Management Aspects of NTN Phase 2	SP-231733	102	Dec.23	Sep.24	TR 28.874
REL-19	FS_5GSAT_APP or FS_5GSAT_Ph3_App	SA6	Study on application enablement for Satellite access enabled 5G Services	SP-231738	102	Dec.23	Sep.24	TR 23.700-01

NOTE: The description above is dedicated to NTN operation via NR.

Work on Machine Type Communication started in 3GPP in Release 10 under LTE.

NB-IoT (Narrowband Internet of Things) was introduced in Release 13 under LTE.

After first, progress was made with preparing for NTN operation via NR in Release 15/16, in Release 17 also corresponding activities started to support NB-IoT and enhanced MTC type of devices via Non-Terrestrial Networks in LTE/EPS.

The start of the WG RAN1 led Release 17 SI "Study on NB-IoT/eMTC support for Non-Terrestrial Networks (NTN)" (FS_LTE_NBIOT_eMTC_NTN) i.e. the study of the LTE based NTN coincided with the start of the normative work for NR based NTN in Release 17 WI NR_NTN_solutions.

In order to simplify the introduction of NTN for LTE, it was assumed to reuse NR NTN functionality (where possible) when introducing NTN for LTE ("NR NTN as baseline"). That is why SI TR 36.763 considers only WG RAN1 and WG RAN2 aspects and assumes that WG RAN3 aspects could be handled in a similar way as NR NTN. However, WG RAN4 aspects were not studied at all in this REL-17 SI due to high workload in RAN4 in REL-17.

This also led to a WGs RAN1/RAN2/RAN3 only Release 17 WI "NB-IoT/eMTC support for Non-Terrestrial Networks" (LTE_NBIOT_eMTC_NTN-Core) missing the corresponding WG RAN4 aspects which were only provided in an early Release 18 WI "NB-IoT (Narrowband IoT)/eMTC (enhanced Machine Type Communication) core & performance requirements for Non-Terrestrial Networks (NTN)" (LTE_NBIOT_eMTC_NTN_req).  The whole functionality could only be considered in place after the WG RAN4 aspects were also completed.

As a consequence, WG RAN5 was defining UE testing for both WIs separately: In a Release 17 WI "UE Conformance - NB-IoT/eMTC support for Non-Terrestrial Networks (NTN) including EPS aspects" (LTE_NBIOT_eMTC_NTN_plus_EPS-UEConTest) testing WGs RAN1/RAN2/RAN3 and TSG CT aspects and a Release 18 WI "LTE_NBIOT_eMTC_NTN_req-UEConTest" (LTE_NBIOT_eMTC_NTN_req-UEConTest) testing the WG RAN4 aspects.

Note: The same assumptions as for NTN for NR were used:

• GNSS capability in the UE for both NB-IoT and eMTC devices. With this assumption, UE can estimate and pre-compensate timing and frequency offset with sufficient accuracy for UL transmission. But simultaneous GNSS and NTN NB-IoT/eMTC operation is not assumed.
• Transparent payload
• Earth-fixed tracking areas

WG SA2 Release 19 stage 2 WI "Architecture support for NB-IoT/eMTC Non-Terrestrial Networks in EPS" (IoT_SAT_ARCH_EPS) introduced minimum essential functionality to support NB-IoT and eMTC over Non-Terrestrial Networks in EPS using 5GSAT_ARCH solutions, e.g. supporting:

• Fixed Earth-based tracking areas, extended NAS timers at least for eMTC when GEO constellations are used
• Policy and QoS control, country-specific CN routing, identification and restriction of satellite access, TA selection, enhanced PLMN selection
• Regulatory services (e.g. Lawful intercept) with super-national satellite ground stations
• Discontinuous coverage (by means of Tracking Area- or RAT-specific configuration of the MME, to ensure that when the UE is unreachable, a) the          UE does not trigger NAS transaction or detach from the network and b) mobile-terminated data destined to the UE can be stored in the network)

Note: The functionality for LTE/EPS is largely aligned with that of Rel-17 NR Non-Terrestrial Networks in 5GS, with the exception of discontinuous coverage that was not considered for NR in Rel-17.

Different types of satellite constellations (LEO, MEO, GEO, OTHERSAT) and radio access types (i.e. WB-EUTRAN, NB-IoT and LTE-M) are distinguished in the core network to allow to identify the access a UE and to adapt accordingly.

The WGs CT1/CT3/CT4/CT6 Release 19 WI "CTx aspects of NB-IoT/eMTC Non-Terrestrial Networks in EPS" (IoT_SAT_ARCH_EPS) realized the stage 3 changes corresponding to the REL-17 SA2 WI.

WG SA5 Release 18 SI "Study on Management Aspects of IoT NTN Enhancements" (FS_IoT_NTN) studies:

• Specific IoT NTN related parameters which should be considered by O&M
• NRM (Network Resource Model) enhancements
• Performance measurements and related new KPIs of IoT NTN

The results were collected in TR 28.841 and the recommendations for the following normative work were:

• Specify/extend SON concepts to allow for moving non-terrestrial NBs.
• Adapt the performance measurements which make use of the HARQ process, which may be unavailable when using satellite RAN.
• Introduce the NRM based on solutions to support handling of coverage holes or discontinuous satellite coverage in a power efficient way.

Note: While the SI focus is clearly on IoT NTN i.e. the NB-IoT/eMTC LTE based NTN, its contents is partly mixing it with NR NTN aspects. So there are some similarities to the REL-17 SI FS_5GSAT_MO and its TR 28.808.

WG SA5 Release 18 WI "Management Aspects of NTN" (OAM_NTN) is the corresponding follow-up WI of REL-18 SI FS_IoT_NTN.

The WG RAN2 led Release 18 WI "IoT (Internet of Things) NTN (non-terrestrial network) enhancements" (IoT_NTN_enh) was focussing on:

• Improving performance (HARQ feedback enabling/disabling; network trigger or network configuration of UE autonomously GNSS measurement).
• Measurement & mobility enhancements in idle as well as connected mode (new time-based and location-based triggers for UE measurements, new SIB to broadcast the neighbor cell/satellite information, satellite ids for serving and neighbor satellites).
• Enhancements for discontinuous coverage (enhancement to RRC Release is introduced, new cause value "Release due to discontinuous coverage" is introduced for the S1AP UE Context Release Request procedure).
• RRM enhancements (related to measurement triggering, GNSS reacquisition, Conditional Handover requirements).

WG RAN4 Release 18 WI "Introduction of FDD LTE band (L+S band) for IoT NTN operation"(IoT_NTN_FDD_LS_band) introduced LTE band 254 for NTN usage.

WG RAN4 Release 18 WI "Introduction of the Extended L-band (UL 1668-1675MHz, DL 1518-1525MHz) for IoT NTN" (IoT_NTN_extLband) introduced LTE band 253 for NTN usage.

WG RAN2 led Release 19 WI "Non-Terrestrial Networks (NTN) for Internet of Things (IoT) Phase 3" (IoT_NTN_Ph3) will work on further enhancements:

• Support of Store&Forward (S&F) satellite operation with full eNB as regenerative payload
• Support of capacity enhancements for uplink (e.g. multiplexing of multiple UEs via orthogonal cover codes (OCC); reduce the necessary uplink and downlink signaling to complete an EDT transaction)

Radio related SIs/WIs for IoT support via NTN:

 

REL	Acronym	led by	Title	description	status report	start	end	further documentation/infos
REL-17	FS_LTE_NBIOT_eMTC_NTN	RAN1	Study on NB-IoT/eMTC support for Non-Terrestrial Networks (NTN)	RP-210868	RP-211506	Dec.19	June 21	connecting LTE NB-IoT and LTE eMTC to NTN (LTE); TR 36.763
REL-17	LTE_NBIOT_eMTC_NTN-Core	RAN1	NB-IoT/eMTC support for Non-Terrestrial Networks	RP-211601	RP-221546	June 21	June 22	RP-221547; no Perf. part
REL-17	LTE_NBIOT_eMTC_NTN_plus_EPS-UEConTest	RAN5	UE Conformance - NB-IoT/eMTC support for Non-Terrestrial Networks (NTN) including EPS aspects	RP-233250	RP-233249	June 22	March 24	tested: REL-17 WI LTE_NBIOT_eMTC_NTN-Core and CT REL-17 WI IoT_SAT_ARCH_EPS
REL-18	LTE_NBIOT_eMTC_NTN_req	RAN4	NB-IoT (Narrowband IoT)/eMTC (enhanced Machine Type Communication) core & performance requirements for Non-Terrestrial Networks (NTN)	RP-223437	RP-231310	March 22	Core: Dec.22 Perf.: June 23	RP-223491; TS 36.102, TS 36.108; RAN4 requirements for REL-17 WI LTE_NBIOT_eMTC_NTN-Core; TS 36.181 bands 255, 256
REL-18	LTE_NBIOT_eMTC_NTN_req-UEConTest	RAN5	UE Conformance - NB-IoT (Narrowband IoT)/eMTC (enhanced Machine Type Communication) core & performance requirements for Non-Terrestrial Networks (NTN)	RP-230285	RP-233415	Dec.22	March 24	tested: REL-18 WI LTE_NBIOT_eMTC_NTN_req; TS 36.521-4
REL-18	IoT_NTN_enh	RAN2	IoT (Internet of Things) NTN (non-terrestrial network) enhancements	RP-234073	RP-233260	Dec.21	Core: Dec.23 Perf.: June 24	RP-233261
REL-18	IoT_NTN_extLband	RAN4	Introduction of the Extended L-band (UL 1668-1675MHz, DL 1518-1525MHz) for IoT NTN	RP-233856	RP-233942	March 23	Core: March 24 Perf.: June 24	UL: 1668-1675MHz, DL: 1518-1525MHz; band 253
REL-18	IoT_NTN_FDD_LS_band	RAN4	Introduction of FDD LTE band (L+S band) for IoT NTN operation	RP-234060	RP-233258	March 23	Core: Dec.23 Perf.: June 24	UL: 1610 – 1626.5 MHz, DL: 2483.5 – 2500 MHz; TR 36.764, band 254
REL-19	IoT_NTN_Ph3	RAN2	Non-Terrestrial Networks (NTN) for Internet of Things (IoT) Phase 3	RP-234077	-	Dec.23	Core: Sep.25

Systems/Core Network related SIs/WIs for IoT support via NTN:

REL	Acronym	led by	Title	description	of TSG#	start	end	further documentation/infos
REL-17	IoT_SAT_ARCH_EPS	SA2	Architecture support for NB-IoT/eMTC Non-Terrestrial Networks in EPS	SP-211306	94e	Sep.21	Dec.21	TS 23.203, TS 23.271, TS 23.401, TS 23.682; SP-220455
REL-17	IoT_SAT_ARCH_EPS	CTx	CTx aspects of NB-IoT/eMTC Non-Terrestrial Networks in EPS	CP-213273	94e	Dec.21	March 22	TS 23.122, TS 23.008, TS 24.008, TS 24.301, TS 27.007; TS 29.212, TS 29.272, TS 29.274, TS 31.102, TS 31.111
REL-18	FS_IoT_NTN	SA5	Study on Management Aspects of IoT NTN Enhancements	SP-220490	96	June 22	June 23	TR 28.841
REL-18	OAM_NTN	SA5	Management Aspects of NTN	SP-230183	99	March 23	Dec.23	TS 28.541, TS 28.552, TS 28.554, TS 28.658

References

Pure Satellite/NTN specific specifications:

TR 38.811, "Study on New Radio (NR) to support non-terrestrial networks", REL-15 SI FS_NR_nonterr_nw, RAN

TR 22.822, "Study on using satellite access in 5G", REL-16 SI FS_5GSAT, SA1

TR 38.821, "Study on solutions for NR to support non-terrestrial networks (NTN)", REL-16 SI FS_NR_NTN_solutions, RAN3

TR 23.737, "Study on architecture aspects for using satellite access in 5G", SI FS_5GSAT_ARCH, SA2; note: SI started in REL-16 but ended in REL-17

TR 38.863, "Non-terrestrial networks (NTN) related RF and co-existence aspects", REL-17 WI NR_NTN_solutions, RAN4

TS 38.101-5, "NR; User Equipment (UE) radio transmission and reception; Part 5: Satellite access Radio Frequency (RF) and performance requirements", REL-17 WI  NR_NTN_solutions, RAN4

TS 38.108, "NR; Satellite Access Node radio transmission and reception", REL-17 WI NR_NTN_solutions, RAN4

TS 38.181, "NR; Satellite Access Node conformance testing", REL-17 WI NR_NTN_solutions, RAN4

TS 38.521-5, "NR; User Equipment (UE) conformance specification; Radio transmission and reception; Part 5: Satellite access Radio Frequency (RF) and performance", REL-17 WI NR_NTN_solutions_plus_CT-UEConTest, RAN5

TR 38.882 "Study on requirements and use cases for network verified UE location for Non-Terrestrial-Networks (NTN) in NR", REL-18 SI FS_NR_NTN_netw_verif_UE_loc, RAN

TR 37.911, "Study on self-evaluation towards the IMT-2020 submission of the 3GPP Satellite Radio Interface Technology", REL-18 SI FS_IMT2020_SAT_eval, SA1

TR 22.926, "Guidelines for extraterritorial 5G Systems (5GS)" REL-18 SI FS_5GET, SA1

Generic specifications including Satellite/NTN aspects:

TS 22.261, "Service requirements for the 5G system", stage 1 spec from SA1

TS 23.501, "System architecture for the 5G System (5GS)", stage 2 spec from SA2, esp. clauses 5.4.10 and 5.4.11

TS 38.300, "NR; NR and NG-RAN Overall description; Stage-2", RAN2, esp. clause 16.14

Note: Stage 3 aspects are distributed over several specifications (like any other 3GPP feature).

Other references:

"NTN & Satellite in Rel-17 & 18", by Munira Jaffar & Nicolas Chuberre, see also 3GPP Highlights newsletter no.3, page 24

 

Abbreviations:

AF                           Application Function

AMF                       Access and Mobility Management Function

AS                           Access Stratum

GEO                        Geostationary Earth Orbit

gNB                        Node providing NR user plane and control plane protocol terminations towards the UE, and connected via the NG interface to the 5GC

GSO                        Geosynchronous Orbit

GNSS                      Global Navigation Satellite System

HAPS                      High Altitude Platform Station

HEO                        Highly Elliptical Orbit

LEO                        Low Earth Orbit

MEO                       Medium Earth Orbiting

NG-RAN                 Next Generation Radio Access Network
(set of gNBs connected to the 5GC through the NG interface)

NGSO                     Non-Geostationary Satellite Orbit

NRM                       Network Resource Model

NTN                        Non-Terrestrial Networks (incl. satellites, UAVs, drones, ballons)

PCI                          Physical Cell Identifier

PLMN                     Public Land Mobile Network

RA                          Random Access

RRC                        Radio Resource Control

RRM                       Radio Resource Management

RTT                         Round Trip Time

SAN                        Satellite Access Node

SSB                         SS/PBCH block

SSC                         Satellite Service Customer

SMTC                     SS/PBCH Block Measurement Timing Configuration

SNO                        Satellite Network Operator

SSB                         SS/PBCH block

TA                           Timing Advance

TAC                        Tracking Area Code

TAI                          Tracking Area Indicator

TN                           Terrestrial Network

TNL                         Transport Network Layer

UAV                        Uncrewed/Uncrewed Aerial Vehicle

UPF                        User Plane Function

VSAT                      Very Small Aperture Terminal

Definitions:

Airborne vehicles: Uncrewed Aircraft Systems (UAS) encompassing tethered UAS (TUA), Lighter than Air UAS (LTA), Heavier than Air UAS (HTA), all operating in altitudes typically between 8 and 50 km including High Altitude Platforms (HAPs)

Geostationary Earth orbit: Circular orbit at 35,786 kilometres above the Earth's equator and following the direction of the Earth's rotation. An object in such an orbit has an orbital period equal to the Earth's rotational period and thus appears motionless, at a fixed position in the sky, to ground observers.

High Altitude Platform Station: airborne vehicle embarking the NTN payload placed at an altitude between 8 and 50 km.

Low Earth Orbit: Orbit around the around Earth with an altitude between 500 kilometres (orbital period of about 88 minutes), and 2,000 kilometres (orbital period of about 127 minutes).

Medium Earth Orbit: region of space around the Earth above low Earth orbit and below geostationary Earth Orbit.

Non-Geosynchronous orbit: earth-centered orbit with an orbital period that does not match Earth's rotation on its axis. This includes Low and Medium Earth Orbit (LEO and MEO).

Non Geostationary Satellites: Satellites (LEO and MEO) orbiting around the Earth with a period that varies approximately between 1.5 hour and 10 hours. It is necessary to have a constellation of several Non Geostationary satellites associated with handover mechanisms to ensure a service continuity.

Non-terrestrial networks: Networks, or segments of networks, using an airborne or space-borne vehicle to embark a transmission equipment relay node or base station.

NTN Gateway: an earth station located at the surface of the earth, providing connectivity to the NTN payload using the feeder link. An NTN Gateway is a TNL node.

NTN payload: a network node, embarked on board a satellite or high altitude platform station, providing connectivity functions, between the service link and the feeder link. In the current version of this specification, the NTN payload is a TNL node.

Regenerative payload: payload that transforms and amplifies an uplink RF signal before transmitting it on the downlink. The transformation of the signal refers to digital processing that may include demodulation, decoding, re-encoding, re-modulation and/or filtering.

Satellite: a space-borne vehicle embarking a bent pipe payload or a regenerative payload telecommunication transmitter, placed into Low-Earth Orbit (LEO) typically at an altitude between 500 km to 2000 km, Medium-Earth Orbit (MEO) typically at an altitude between 8000 to 20000 km, or Geostationary-satellite Earth Orbit (GEO) at 35 786 km altitude.

Satellite Access Node (SAN): node providing NR user plane and control plane protocol terminations towards NTN Satellite capable UE, and connected via the NG interface to the 5GC. It encompass a transparent NTN payload on board a NTN platform, a gateway and gNB functions.

Space-borne vehicles: Satellites including Low Earth Orbiting (LEO) satellites, Medium Earth Orbiting (MEO) satellites, Geostationary Earth Orbiting (GEO) satellites as well as Highly Elliptical Orbiting (HEO) satellites

Service link: wireless link between the NTN payload and UE

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IMPORTANT NOTE:
Please be aware that these pages are a snapshot of the work going on in 3GPP.
All work items of 3GPP are contained in the Work Plan (https://www.3gpp.org/ftp/Information/WORK_PLAN/) where you can search for ‘ACRONYM’ in the acronym field of the Excel sheet.