4 NR over satellite, release by release

4.1 One line of work, six releases long

The vocabulary chapter defined the pieces. This chapter follows the one line of work that put NR — 5G's radio — on a satellite, from the first study to the Release 20 split, and it does it in the order the plenaries approved things.

Two habits run through it and are worth naming in advance.

Homework comes first. Two study reports were written before a single binding sentence, and every later work item still refers back to them.

Each release starts by writing down what the last one assumed. That is why the justifications quoted in Why anyone wanted it, and who said so read like a running list of constraints, each release loosening one.

4.2 Release 15: is this even possible

The line begins with a single work plan row — the only satellite row in the whole of Release 15 Rel-15.

FS_NR_nonterr_nw, the study on NR to support non-terrestrial networks, is led by RAN1: its own leadership line names RAN1 as the primary responsible working group FS_NR_nonterr_nw.

Its revised study document, RP-171450, came from THALES and was approved at RAN#76 RP-171450, which sat in West Palm Beach, Florida, in June 2017 RP-76.

What it produced is TR 38.811, the study on New Radio to support non-terrestrial networks, which exists in one version, for Release 15 TR 38.811.

The study carries 124 documents ^[5]. That is a small number for something the whole line rests on, and it is what a feasibility question looks like in paperwork: a few dozen papers, one report, and permission to go further.

4.3 Release 16: what would it actually take

The second study asked the harder question, and its objective says exactly what it was allowed to assume:

Three things in one sentence. It is bound to the first report. Its priority is satellite access rather than aircraft. And unmanned aircraft and high altitude platforms are treated as an easier version of the same problem — less delay, less Doppler shift from the vehicle's own speed.

The leadership line changed here: FS_NR_NTN_solutions names RAN3 as the leading working group, with RAN1 and RAN2 second FS_NR_NTN_solutions.

This is the only piece of the NR line that RAN3 leads, and it fits: the study had to work out how the network side is arranged, not just how the air interface copes.

Its study document, RP-190710, again from Thales, was approved at RAN#83 RP-190710 in Shenzhen in March 2019 RP-83. The report is TR 38.821, which also exists in one version only, for Release 16 TR 38.821.

794 documents carry this short name ^[6] — several times the first study, and a fair sign of how much harder the second question was.

4.4 Release 17: the rules, and the biggest pile in the subject

NR_NTN_solutions is where homework becomes obligation. Its leadership line names RAN2 as the leading working group with RAN1, RAN3 and RAN4 behind it NR_NTN_solutions, and its objective sets out the scope:

Two constraints to hold on to. LEO and GEO especially — low earth orbit and geostationary, the two orbits TS 38.108's own definition of a satellite names ^[7]. And FDD is assumed: frequency division duplex, sending and receiving on two separate frequencies at once.

That assumption is what a Release 19 item on the older radio later had to work around, in The same idea on the older radio, for things that are not phones.

4.4.1 What it created and what it changed

The work plan lists two documents this item creates: TS 38.108, the satellite access node's radio transmission and reception, and TS 38.181, its conformance tests NR_NTN_solutions TS 38.108 TS 38.181.

Its own work item description goes much further and lists 25 documents it creates or changes NR_NTN_solutions. They cover, in one sweep, the whole stack of an NR radio network:

• The physical layer — physical channels and modulation TS 38.211, and the layer procedures for control and for data TS 38.213 TS 38.214.

• The protocol layers — medium access control TS 38.321, radio link control, packet data convergence, and radio resource control TS 38.331.

• The system view — the overall description TS 38.300, idle-mode procedures TS 38.304, device capabilities TS 38.306 and release-independent bands TS 38.307.

• The network interfaces — the NG application protocol TS 38.413 and the Xn one between base stations TS 38.423.

• The radio requirements — radio resource management TS 38.133, the device's own radio requirements TS 38.101-5, and the coexistence report TR 38.863 TR 38.863.

That is what a feature costs when it is genuinely new: not one document, but a list long enough that four working groups had to be named on the row.

4.4.2 The size of it

The core part of this work item is the single largest short name in the whole register: 4346 documents, over 140 meetings ^[8]. The performance part carries 778 ^[9] and the feature row itself 781 ^[10].

Its conformance part, which is RAN5's, carries 1008 on its own ^[11]. Four rows, four counts, and — as How the work is cut up, and who carries it warns — never a sum.

The four rows were also planned to finish at very different times, and the work plan's planned days show the shape of it.

The core part was planned to 2022-06-06, the performance part to 2023-03-03, the feature row itself to 2024-12-12 and the conformance part to 2025-12-12 NR_NTN_solutions-Core NR_NTN_solutions-Perf NR_NTN_solutions NR_NTN_solutions_plus_CT-UEConTest.

Rules first, then what has to be measured, then the tests that prove a real device meets them. A feature is not done when its core part is done, and the gap between the two ends of that list is where most of the argument about whether something "exists" comes from.

4.5 Release 18: enhancements, and the assumptions being loosened

NR_NTN_enh keeps RAN2 as leading working group, with RAN1, RAN3 and RAN4 secondary NR_NTN_enh. Its objective widens the orbits:

Release 17 said LEO and GEO. Release 18 says geosynchronous and non-geosynchronous, and spells out that the second includes medium earth orbit. That is a wider door, and it was opened deliberately.

Its justification, quoted in full in Why anyone wanted it, and who said so, is the clearest statement anywhere of what Release 17 had taken for granted: a transparent payload, power class 3 devices with a satellite navigation receiver, in earth-fixed or moving cells ^[12].

The work item description the work plan points at is RP-232669, from Thales, approved at RAN#101 RP-232669.

Its core part carries 3249 documents ^[13], its performance part 326 ^[14] and the feature row 486 ^[15].

Among the documents its own description names is one that had not existed before: TS 38.108, created by Release 17, is now on the list of things Release 18 changes NR_NTN_enh TS 38.108. That is the shelf starting to maintain itself.

Two of its other targets show how far outside the radio the enhancements reached.

It names the positioning protocol, for a network-checked device location, and the positioning protocol between network nodes. Its own description flags possible cooperation with SA2, SA3 and SA4 over exactly those points, which no other item on this line does NR_NTN_enh.

The one report that runs the whole length of this line is TR 38.863, the radio-frequency and coexistence work.

Its own scope says it covers those aspects of the Release 17 work item ^[16], and it is named as a target by Release 17, 18 and 19 alike, and by the Release 20 guard band item TR 38.863.

Living beside other users of the spectrum is not a phase of this work; it is a running cost of it.

4.6 Release 19: phase 3

NR_NTN_Ph3 keeps the same shape and the same leadership — RAN2 leading, RAN1, RAN3 and RAN4 secondary NR_NTN_Ph3:

Read it beside the Release 18 one and the difference is a single word: further. The orbit assumptions are unchanged, and the aircraft compatibility clause has gone. This is a release consolidating rather than opening ground.

Its justification is two sentences of history and nothing else — Release 17 defined the solutions, Release 18 introduced enhancements ^[17].

The work item description is RP-251954, from THALES and CATT, approved at RAN#109 RP-251954. The core part carries 2807 documents over 80 meetings ^[18], and the feature row 190 ^[19].

The work plan gives the feature row a completion value of 0.8, and its core part a value of 1 NR_NTN_Ph3 NR_NTN_Ph3-Core. That number is the only thing the work plan says about progress: there is no field anywhere that says running, stopped or finished.

4.7 How to read a leadership line, and why it has to be read

Every claim in this chapter about which group leads what came out of one field, and it is worth knowing why no shortcut was taken.

The register carries, for each group, a list of every work item whose leadership line mentions it — leading and secondary together, in one list. RAN4's list runs to dozens of items RAN4, and almost none of them is an item RAN4 leads.

That field cannot answer "who leads this", and using it as if it could is the single easiest mistake to make with this data.

The answer is in the work item's own leadership line, and only there, because it is free text somebody typed. So it has to be read rather than looked up, and the four NR lines read differently every time:

Work item	What its leadership line says
FS_NR_nonterr_nw	primary responsible working group TSG-RAN1 FS_NR_nonterr_nw
FS_NR_NTN_solutions	leading working group RAN3, secondary RAN1 and RAN2 FS_NR_NTN_solutions
NR_NTN_solutions	leading working group RAN2, secondary RAN1, 3, 4 NR_NTN_solutions
NR_NTN_Ph3	RAN2, secondary responsible working groups RAN1, RAN3, RAN4 NR_NTN_Ph3

Four items, four spellings, one meaning each. There is no column anywhere that holds the answer in a fixed shape, which is why this course names a leading group only where that line names one.

4.8 Release 20: one item becomes several

Release 17, 18 and 19 each had one big NR item. Release 20 does not. Instead there are narrow items, each with its own leading group and its own short list of documents.

Working without a satellite navigation fix. NR_NTN_GNSS_resilient is led by RAN1, with RAN4 and RAN2 secondary NR_NTN_GNSS_resilient. The work plan gives it a completion value of 0, and its work item description RP-261568, from THALES, was approved at RAN#112 RP-261568 — Singapore, June 2026 RP-112. The study behind it produced TR 38.742, whose scope says it evaluates and defines solutions for keeping NR-NTN working where the navigation system is temporarily unavailable TR 38.742 ^[20]. The study itself carries 330 documents ^[21].

An extended guard band. NR_NTN_IoT_NTN_ext_guard names RAN WG4 as its leading group NR_NTN_IoT_NTN_ext_guard. A guard band is empty spectrum left at the edge of a band so that transmissions do not spill into the neighbours. Its work item description RP-261532 was approved at RAN#112, and it is signed not by one company but by a long list of them, from satellite operators to chip makers RP-261532. The work plan gives the row a completion value of 0 and no documents yet NR_NTN_IoT_NTN_ext_guard.

Higher power classes and a narrow channel. NTN_bands_Features_R20, also led by RAN WG4, introduces higher power classes, a 3 MHz channel bandwidth and a device class the work plan calls eRedCap, for the bands that already exist NTN_bands_Features_R20. Nothing in this register expands that last name, so nothing here says what it stands for. Its description RP-261551, from Apple, was approved at RAN#112 RP-261551.

Those three touch the same handful of documents over and over: the device's radio requirements TS 38.101-5, the node's TS 38.108, and the coexistence report TR 38.863.

4.8.1 Moving a device between the two networks

Two items are about the seam between an ordinary ground network and a satellite one. They are a pair, and the record gives them different titles in different releases.

The Release 19 one is LTE_TN_NR_NTN_mob, titled inter-RAT mode mobility support from an E-UTRAN ground network to NR NTN, led by RAN2 with no secondary group named on its line LTE_TN_NR_NTN_mob. Its description RP-240924, from THALES, was approved at RAN#104 RP-240924, and it changes three LTE documents: the overall description TS 36.300, device capabilities TS 36.306 and radio resource control TS 36.331.

The Release 20 one is LTE_TN_NR_NTN_HO, titled E-UTRA TN to NR NTN handover enhancements, led by RAN WG2 with RAN WG4 secondary LTE_TN_NR_NTN_HO. Its description RP-252890, from CATT, was approved at RAN#109 RP-252890, and it changes the same three documents plus radio resource management TS 36.133.

The difference the record actually gives is the difference between those two titles — one says mobility support, the other says handover enhancements — and the second one adds RAN4 and a fourth document. Nothing here says more than that, and this course does not fill the gap in.

4.9 The whole line in one table

Release	Short name	Leading group	Documents on the biggest row
Rel-15	FS_NR_nonterr_nw	RAN1	124 [5]
Rel-16	FS_NR_NTN_solutions	RAN3	794 [6]
Rel-17	NR_NTN_solutions	RAN2	4346 [8]
Rel-18	NR_NTN_enh	RAN2	3249 [13]
Rel-19	NR_NTN_Ph3	RAN2	2807 [18]
Rel-20	narrower items, one per problem	RAN1, RAN2 and RAN4 between them	—

The last row is the point of the table. For five releases this line was one big item with one leading group. In Release 20 it is not: resilience without a navigation fix belongs to RAN1, the guard band and the band features to RAN4, and the two mobility items to RAN2.

That is what a subject looks like once the hard general problem has been solved and what is left is a list of specific ones.

4.10 Where this line meets everything else

The same phases exist on the older radio for things that are not phones, and that is The same idea on the older radio, for things that are not phones — including one Release 20 item, the extended guard band, that belongs to both lines at once.

The counts above sit inside the frame set out in How the work is cut up, and who carries it, and the reasons the groups gave for each step are Why anyone wanted it, and who said so.

To read the line in the original, take it in the order it was written: TR 38.811 TR 38.811, then TR 38.821 TR 38.821, then TS 38.108 for what a satellite base station has to be TS 38.108 and TS 38.181 for how that is proved TS 38.181.