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Content for  TR 38.821  Word version:  16.2.0

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4 Non-Terrestrial Networks overview and scenarios  4.1 Non-Terrestrial Networks overview  4.2 Non-Terrestrial Networks reference scenarios 
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4  Non-Terrestrial Networks overview and scenarios  p. 15

4.1  Non-Terrestrial Networks overview  p. 15

A non-terrestrial network refers to a network, or segment of networks using RF resources on board a satellite (or UAS platform).
The typical scenario of a non-terrestrial network providing access to user equipment is depicted below:
Reproduction of 3GPP TS 38.821, Fig. 4.1-1: Non-terrestrial network typical scenario based on transparent payload
Figure 4.1-1: Non-terrestrial network typical scenario based on transparent payload
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Reproduction of 3GPP TS 38.821, Fig. 4.1-2: Non-terrestrial network typical scenario based on regenerative payload
Figure 4.1-2: Non-terrestrial network typical scenario based on regenerative payload
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Non-Terrestrial Network typically features the following elements:
  • One or several sat-gateways that connect the Non-Terrestrial Network to a public data network
    • a GEO satellite is fed by one or several sat-gateways which are deployed across the satellite targeted coverage (e.g. regional or even continental coverage). We assume that UE in a cell are served by only one sat-gateway
    • A Non-GEO satellite served successively by one or several sat-gateways at a time. The system ensures service and feeder link continuity between the successive serving sat-gateways with sufficient time duration to proceed with mobility anchoring and hand-over
  • A Feeder link or radio link between a sat-gateway and the satellite (or UAS platform)
  • A service link or radio link between the user equipment and the satellite (or UAS platform).
  • A satellite (or UAS platform) which may implement either a transparent or a regenerative (with on board processing) payload. The satellite (or UAS platform) generate beams typically generate several beams over a given service area bounded by its field of view. The footprints of the beams are typically of elliptic shape. The field of view of a satellites (or UAS platforms) depends on the on board antenna diagram and min elevation angle.
    • A transparent payload: Radio Frequency filtering, Frequency conversion and amplification. Hence, the waveform signal repeated by the payload is un-changed;
    • A regenerative payload: Radio Frequency filtering, Frequency conversion and amplification as well as demodulation/decoding, switch and/or routing, coding/modulation. This is effectively equivalent to having all or part of base station functions (e.g. gNB) on board the satellite (or UAS platform).
  • Inter-satellite links (ISL) optionally in case of a constellation of satellites. This will require regenerative payloads on board the satellites. ISL may operate in RF frequency or optical bands.
  • User Equipment are served by the satellite (or UAS platform) within the targeted service area.
There may be different types of satellites (or UAS platforms) listed here under:
Platforms Altitude range Orbit Typical beam footprint size
Low-Earth Orbit (LEO) satellite300 - 1500 kmCircular around the earth100 - 1000 km
Medium-Earth Orbit (MEO) satellite7000 - 25000 km100 - 1000 km
Geostationary Earth Orbit (GEO) satellite35 786 kmnotional station keeping position fixed in terms of elevation/azimuth with respect to a given earth point200 - 3500 km
UAS platform (including HAPS)8 - 50 km (20 km for HAPS)5 - 200 km
High Elliptical Orbit (HEO) satellite400 - 50000 kmElliptical around the earth200 - 3500 km
Typically
  • GEO satellite and UAS are used to provide continental, regional or local service.
  • a constellation of LEO and MEO is used to provide services in both Northern and Southern hemispheres. In some case, the constellation can even provide global coverage including polar regions. For the later, this requires appropriate orbit inclination, sufficient beams generated and inter-satellite links.
HEO satellite systems are not considered in this document.
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4.2  Non-Terrestrial Networks reference scenarios  p. 16

We shall consider in this document non-terrestrial networks providing access to user equipment in six reference scenarios including
  • Circular orbiting and notional station keeping platforms.
  • Highest RTD constraint
  • Highest Doppler constraint
  • A transparent and a regenerative payload
  • One ISL case and one without ISL. Regenerative payload is mandatory in the case of inter-satellite links.
  • Fixed or steerable beams resulting respectively in moving or fixed beam foot print on the ground
Six scenarios are considered as depicted in Table 4.2-1 and are detailed in Table 4.2-2.
Transparent satellite Regenerative satellite
GEO based non-terrestrial access networkScenario AScenario B
LEO based non-terrestrial access network: steerable beamsScenario C1Scenario D1
LEO based non-terrestrial access network: the beams move with the satelliteScenario C2Scenario D2
Scenarios GEO based non-terrestrial access network (Scenario A and B) LEO based non-terrestrial access network (Scenario C & D)
Orbit typenotional station keeping position fixed in terms of elevation/azimuth with respect to a given earth pointcircular orbiting around the earth
Altitude35,786 km600 km
1,200 km
Spectrum (service link)<6 GHz (e.g. 2 GHz)
>6 GHz (e.g. DL 20 GHz, UL 30 GHz)
Max channel bandwidth capability (service link)30 MHz for band < 6 GHz
1 GHz for band > 6 GHz
PayloadScenario A: Transparent (including radio frequency function only)
Scenario B: regenerative (including all or part of RAN functions)		Scenario C: Transparent (including radio frequency function only)
Scenario D: Regenerative (including all or part of RAN functions)
Inter-Satellite linkNoScenario C: No
Scenario D: Yes/No (Both cases are possible.)
Earth-fixed beamsYesScenario C1: Yes (steerable beams), see note 1
Scenario C2: No (the beams move with the satellite)
Scenario D 1: Yes (steerable beams), see note 1
Scenario D 2: No (the beams move with the satellite)
Max beam foot print size (edge to edge) regardless of the elevation angle3500 km (Note 5)1000 km
Min Elevation angle for both sat-gateway and user equipment10° for service link and 10° for feeder link10° for service link and 10° for feeder link
Max distance between satellite and user equipment at min elevation angle40,581 km1,932 km (600 km altitude)
3,131 km (1,200 km altitude)
Max Round Trip Delay (propagation delay only)Scenario A: 541.46 ms (service and feeder links)
Scenario B: 270.73 ms (service link only) 		Scenario C: (transparent payload: service and feeder links)
25.77 ms (600km)
41.77 ms (1200km)
Scenario D: (regenerative payload: service link only)
12.89 ms (600km)
20.89 ms (1200km)
Max differential delay within a cell (Note 6)10.3 ms3.12 ms and 3.18 ms for respectively 600km and 1200km
Max Doppler shift (earth fixed user equipment)0.93 ppm24 ppm (600km)
21ppm (1200km)
Max Doppler shift variation (earth fixed user equipment)0.000 045 ppm/s0.27ppm/s (600km)
0.13ppm/s (1200km)
User equipment motion on the earth1200 km/h (e.g. aircraft)500 km/h (e.g. high speed train)
Possibly 1200 km/h (e.g. aircraft)
User equipment antenna typesOmnidirectional antenna (linear polarisation), assuming 0 dBi
Directive antenna (up to 60 cm equivalent aperture diameter in circular polarisation)
User equipment Tx powerOmnidirectional antenna: UE power class 3 with up to 200 mW
Directive antenna: up to 20 W
User equipment Noise figureOmnidirectional antenna: 7 dB
Directive antenna: 1.2 dB
Service link3GPP defined New Radio
Feeder link3GPP or non-3GPP defined Radio interface3GPP or non-3GPP defined Radio interface
NOTE 1:
Each satellite has the capability to steer beams towards fixed points on earth using beamforming techniques. This is applicable for a period of time corresponding to the visibility time of the satellite
NOTE 2:
Max delay variation within a beam (earth fixed user equipment) is calculated based on Min Elevation angle for both gateway and user equipment
NOTE 3:
Max differential delay within a beam is calculated based on Max beam foot print diameter at nadir
NOTE 4:
Speed of light used for delay calculation is 299792458 m/s.
NOTE 5:
The Maximum beam foot print size for GEO is based on current state of the art GEO High Throughput systems, assuming either spot beams at the edge of coverage (low elevation).
NOTE 6:
The maximum differential delay at cell level has been computed considering the one at beam level for largest beam size. It does not preclude that cell may include more than one beam when beam size are small or medium size. However the cumulated differential delay of all beams within a cell will not exceed the maximum differential delay at cell level in the Table above.
The NTN study results apply to GEO scenarios as well as all NGSO scenarios with circular orbit at altitude greater than or equal to 600 km.
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