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3GPP TR 24.821 衛星アクセス向けのPLMN選択メモ

2023/01/02に公開約16,300字

はじめに

3GPP TR 24.821 Study on PLMN selection for satellite access (Release 17)をザクッと斜め読みしたときのメモです。

まとめ

  • PLMN側でUEの位置情報をみて登録を拒否。"PLMN not allowed to operate at the present UE location"を返却する。UEは、PLMN選択手順に入るが"PLMN not allowed to operate at the present UE location"を返却したPLMNは衛星アクセスのPLMN候補としてもう利用しない。もしNWがMCCとして国情報を与えていたとき、UEは同じ国のPLMN(MCCが同じPLMN)を衛星アクセスのPLMN候補として利用してもいい。
  • 国際エリアにイン・アウトするときにPLMN選択をトリガしてもよい(実装依存)。
  • PLMN選択のために衛星NG-RANは新しくRATとして定義する。
  • UEが高優先PLMNの周期サーチをするとき、候補PLMNまたはサービングPLMNがshared MCCのときは、MCCの値により候補となるPLMNを落としてはならない。
  • USIMのEFファイルに新しいRATを追加する。(CT6)
  • 衛星アクセスの複数利用可能なPLMNでの優先順位は、CT6でRAT識別子を追加することで対応する。
  • 衛星アクセスでの高優先PLMN向けの周期サーチは必要。TS 23.122に導入される。
  • 周期サーチの間隔の新しい値は導入されなかった。
  • RPLMNの国/MCCにマッチするMCCのPLMNに限定して、高優先PLMNサーチを行うかは結論が出なかった。
  • UEが位置する国での動作が許可されてないことをPLMNが示すときは、そのPLMNで緊急呼を試みてはいけない。

シナリオ

シナリオA

  • 国Aをカバーするように衛星セルが向けられる。
  • 国A向けのPLMN IDをブロードキャストしている。
  • 意図しないCross-border leakageが発生してしまう。

シナリオB

  • 複数の国をまたがっている。国A,B,Cにサービスを提供。
  • 意図しないCross-border leakageが国Dに発生してしまう。
  • 欧州や中央アメリカ、中東など比較的小さな国が接しているときに発生。

さらに、3つのシナリオに分けられる。
Scenario B1: Three PLMN IDs are broadcast, with three different MCCs corresponding to Country A, Country B and Country C, respectively. This scenario assumes that the PLMN operator is registered and obtains MNC in each country.
Scenario B2: Single PLMN ID corresponding to one country (Country A) is broadcast. Extra-territorial use of a PLMN ID, along with the conditions for such use, is defined in ITU-T E.212 [6] (see Annex E).
Scenario B3: PLMN ID with a global/shared PLMN ID (with MCC 9xx) is broadcast. The use of global/shared PLMN ID, along with the associated conditions, is defined in ITU-T E.212 [6] (see Annex A and clause F.6).

シナリオC

  • 島国や海に面している国に海にまでサービスを提供。
  • 日本のようなケース。国AのPLMN IDを使う。
  • international waterにleakageが発生することがある。

シナリオD

  • international areaのカバレッジを持つ。
  • 国Aにleakageが発生することがある。

さらに、2つのシナリオに分けられる。
Scenario D1: The PLMN ID broadcast in the cell is a global/shared PLMN ID (with MCC 9xx)
Scenario D2: The PLMN ID broadcast in the cell is the PLMN ID of the operator of the PLMN. The MCC will be the MCC of the home country of the PLMN.

しかし、このシナリオは次にような課題がある。(ただ、PLMN選択には関係ない)

  • Maritime MSSの周波数割当は他のMSSと関係が少ない
  • 国際周波数干渉調整
  • 低い電力効率(ユーザ密度が小さい)

課題

Key issue #1: Determination of the country of the UE's location

In [8], SA3-LI has established the requirement that "Any solution shall support the ability to enforce the use of a Core Network of PLMN in the country where the UE is physically located". This means that, if the UE is able to determine the country of its physical location, it use this to select a PLMN. This goes beyond the requirements in the legacy PLMN selection procedure in 3GPP TS 23.122 [3], where the country is defined by the MCC or a range of MCCs (see 3GPP TS 23.122 [3]), of the serving PLMN.

UEが物理的に位置する国のPLMNのコアネットワークを利用しないといけない。
既存の前提では、MCCから国の判断はできるが、衛星アクセスでは機能しない。
なぜなら

  • a 3GPP satellite access cell may span across multiple countries;
  • there are global/shared PLMN IDs with MCC that does not correspond to any country (MCC 9xx); and
  • in international areas, the UE cannot rely on the MCC.

どうやって利用している国を特定するのか?

Key issue #2: Use of core network of PLMN in country where UE is located

課題1と似ているけど、課題1で国を特定した上で(determined country)、ある国の中で適切なコアネットワークを選択する、ということか。

The following questions are expected to be studied within this key issue:

  • how the UE determines which PLMN(s) can be selected in determined country of its physical location (if it is determined that the UE is not in an international area);
  • what information could be available to the UE to help in selecting, in a given country, a PLMN whose CN is physically located in the same country as the UE:
    • pre-configured in the UE; and
    • provided by PLMN.

Key issue #3: PLMN selection in international areas

シナリオDでの課題

Satellite access networks are expected to cover large portions of the globe. This includes international areas. Additionally, in [8], SA3-LI also provided requirements specific to international areas: "Any solution addressing extraterritorial (e.g. international maritime zone and aeronautical) use cases should provide means to notify the HPLMN on roaming in and out of those areas".

Key issue #4: Handling of shared/global PLMN IDs

Key issue #5: Handling of new satellite RAT

SA1 has specified a new Access Technology Identifier "satellite NG-RAN" to be used in the Operator Controlled PLMN Selector list and the User Controlled PLMN Selector list in USIM (see 3GPP TS 22.011 [11]). SA2 has specified deployment scenarios in which a PLMN deploys both terrestrial and satellite access with overlapping coverage (see 3GPP TR 23.737 [5]).

Operator Controlled PLMN, User Controlled PLMNにも衛星のRAT識別子が追加されてる。
USIMのPLMN選択手順にインパクトあり。優先順位。

Key issue #6: PLMN search for satellite access

The range for the search interval for periodic search for higher priority PLMNs is specified in TS 23.122 [3]. Currently, there are two different search interval ranges: for non-NB-IoT UE, and for NB-IoT UE, respectively. What interval will be used for PLMN search in satellite access needs to be studied.

サーチインターバル:non-NB-IoT UE or NB-IoT UE

In the legacy PLMN selection procedure, the UE searches for higher priority PLMN only among PLMNs with the same country as the RPLMN. It needs to be studied whether this rule should remain for satellite access.

Key issue #7: Emergency calls

Satellite access networks are expected to cover the large geographical areas which cover some countries and several PLMNs from the legacy communication system perspective. To support emergency call services for UE might be influenced by adopting satellite access. Therefore, it is needed to study for the routing of emergency call to appropriate PSAP in the case of adopting satellite access.

結論

解決策、評価は飛ばして結論のみまとめる。

8.1 Conclusion for key issue 1

There are no conclusions for this key issue.

8.2 Conclusion for key issue 2

  • PLMN側でUEの位置情報をみて登録を拒否。"PLMN not allowed to operate at the present UE location"を返却する。
  • UEは、PLMN選択手順に入る。"PLMN not allowed to operate at the present UE location"を返却したPLMNは衛星アクセスのPLMN候補としてもう利用しない。
  • もしNWがMCCとして国情報を与えていたとき、UEは同じ国のPLMN(MCCが同じPLMN)を衛星アクセスのPLMN候補として利用してもいい。

KI#2 on PLMN search resulting from network informing the UE that NW is unable to provide service to UE's physical location has the following study points:
a) how the UE determines which PLMN(s) can be selected in determined country of its physical location (if it is determined that the UE is not in an international area);
b) what information could be available to the UE to help in selecting, in a given country, a PLMN whose CN is physically located in the same country as the UE:
pre-configured in the UE; and
provided by PLMN.

In the normative phase, for study point a), when the UE is rejected by the NW with the indication "PLMN not allowed to operate at the present UE location", the UE shall enter PLMN selection procedures detailed in 3GPP TS 23.122 [3], sublause 4.4.3.1 on "At switch on or recovery from lack of coverage" but with the following additional requirements:

  1. the PLMN that provide the reject cause "PLMN not allowed to operate at the present UE location" shall not be considered as a candidate for PLMN selection for satellite NG-RAN access. The scope and duration that this PLMN is considered as not allowed for NTN access will be dealt with in normative phase; and
  2. if NW has provided an indication of the country of UE location in the form of one or more MCCs, and the HPLMN has configured the UE to take the network indicated information into account, then the UE should consider PLMN of the same country – as defined in 3GPP TS 23.122 [3] - as the indicated MCCs, or PLMNs with a shared MCC as defined in ITU-T E.212 [6] clause F.6, as candidates for satellite NG-RAN access for PLMN selection.

For study point b), with regards to information to assist the UE in selecting in a given country, PLMNs whose CN is physically located in same country as the UE:-

  • no locally pre-configured information and mappings in the UE that negatively bias operator and user PLMN selection rules and prioitization (such as deprioitising the entries in the User Controlled PLMN selector and Operator Controlled PLMN selector lists) as set out in 3GPP TS 22.011 [11] clause 3.2, shall be progressed in normative phase; and
  • only the AMF provided information as detailed in SA2's CR in S2-2101667 shall be progressed in normative phase.

8.3 Conclusion for key issue 3

  • 国際エリアにイン・アウトするときにPLMN選択をトリガしてもよい(実装依存)。

Key issue 3 was about PLMN selection in international areas.
The following is the list of the issues studied in this key issue and the respective conclusions for the normative phase:
a) how the UE selects PLMN if it is determined that the UE is in an international area; and
b) what information could be available to aid in PLMN selection in international areas:

  • pre-configured in the UE; and
  • provided by PLMN.
    For a), the following conclusion is adopted to proceed to the normative phase:
  • As implementation option, upon a transition in and out of international areas, the UE may trigger a PLMN selection.
    For b), no conclusions have been agreed to proceed to the normative phase in Release 17.

8.4 Conclusion for key issue 4

  • UEが高優先PLMNの周期サーチをするとき、候補PLMNまたはサービングPLMNがshared MCCのときは、MCCの値により候補となるPLMNを落としてはならない。

Key issue 4 was about Handling of shared/global PLMN IDs.
The following is the list of the issues studied in this key issue and the respective conclusions for the normative phase:
a) what modifications are needed to the PLMN selection procedure to handle shared/global PLMN IDs
b) should these changes also apply to the legacy PLMN selection procedure;
c) what information could be available to aid in handling shared/global PLMN IDs:
▪ pre-configured in the UE; and
▪ provided by PLMN; and
d) how to accommodate LI requirements when handling shared/global PLMN IDs.
For a), the following conclusion is adopted:
When the UE is performing periodic search for higher priority PLMN, the UE should not eliminate any candidate PLMN due to the value of its MCC not representing the same country as the MCC of the serving PLMN if:

  1. The candidate PLMN has a PLMN ID with shared MCC; or
  2. The serving PLMN has a PLMN ID with shared MCC.
    For b), the changes should apply to non-terrestrial access only.
    For c), no information needs to be pre-configured in the UE or provided by the PLMN to aid in handling of shared/global PLMN ID within the scope of key issue 4.
    NOTE: Information may be provided to the UE as part of the solutions to other key issues.
    For d), no solution is needed under key issue 4. This issue is handled under key issue 2.

8.5 Conclusion for key issue 5

  • PLMN選択のために衛星NG-RANは新しくRATとして定義する。
  • USIMのEFファイルに新しいRATを追加する。(CT6)

The following is the list of the issues studied in this key issue and the respective conclusions for the normative phase:
a) what is the prioritization of the new RAT and how it is implemented in the PLMN selection procedure; and
b) what information is configured in the UE related to RAT prioritization.
For a), the following conclusion is adopted:

  • Satellite NG-RAN is defined as a new radio access technology for PLMN selection.
    For b) the following conclusion is adopted:
  • New Access Technology Identifier in the appropriate EF files in USIM (under the responsibility of CT6).

8.6 Conclusion for key issue 6

  • 衛星アクセスの複数利用可能なPLMNでの優先順位は、CT6でRAT識別子を追加することで対応する。
  • 衛星アクセスでの高優先PLMN向けの周期サーチは必要。TS 23.122に導入される。
  • 周期サーチの間隔の新しい値は導入されなかった。
  • RPLMNの国/MCCにマッチするMCCのPLMNに限定して、高優先PLMNサーチを行うかは結論が出なかった。

KI#6 on PLMN search for satellite access has the following study points:-
a) Whether there are different priority levels for available PLMNs in satellite access?
b) Whether the periodic search for higher priority PLMNs in satellite access is needed? and
c) Whether the need to have a separate range of values for the search interval for periodic search for higher priority PLMNs in satellite access.
d) Whether the search for higher priority PLMN should be limited to PLMNs where MCC matches the MCC or country of the RPLMN.
For study point a),

  • Other than CT6's responsibilities for introducing an access technology identifier to for satellite NG-RAN, and the use of this new access technology identifier in CT1 TSes, no normative work is needed by CT1.
    For study point b),
  • Yes, periodic search for higher priority PLMNs in satellite access is needed. In normative phase, requirements for periodic search for higher priority PLMNs in satellite access will be introduced to 3GPP TS 23.122 [3].
    For study point c),
  • A new range of values for the search interval for periodic search for higher priority PLMNs in satellite access is not needed. No normative work is needed other than documenting the resuse of existing ranges for timer T to be used for satellite access.
    For study point d),
  • Only solution#13 covers this study point d). However, solution#13 has outstanding Editor's notes, leaving the proposed solution unclear.
  • In normative phase, no solution for study point d) will be pursued and thus the search for higher priority PLMN will remain as it is currently specified in 3GPP TS 23.122 [3].

8.7 Conclusion for key issue 7

  • UEが位置する国での動作が許可されてないことをPLMNが示すときは、そのPLMNで緊急呼を試みてはいけない。

For this Key issue, SA1 provided a guidance by SA1 LS reply (S1-211319) as follows:
The UE should first determine a most suitable PLMN based on its own physical location determination. As there may be border cases where the UE cannot determine sufficiently accurate or sufficiently precise in which country it is, the UE may also still attempt to obtain (emergency) services from a PLMN that according to the UE is not allowed to operate in the country of the UE's location. If the PLMN indicates it is not allowed to operate in the country of the UE's location, the UE should not (re)-attempt emergency calls.
Based on the above requirements, the following conclusions are adopted:

  • If a PLMN indicates it is not allowed to operate in the country of the UE's location, the UE should not (re)-attempt emergency calls in that PLMN.
  • Otherwise, if the UE is unable to obtain normal services from any PLMN, the UE may attempt to obtain emergency services from any available PLMN.

Normative Phase

Work Item Code

911030 - 5GSAT_ARCH_CT

TS 23.122

Access Technology Identifier "satellite NG-RAN" C1-212407

Validity of cause code #78 C1-221824

x

Higher priority PLMN search for MS in satellite NG-RAN access C1-220742

x

Interval of Time between Searches for Higher Priority PLMN via Satellite NG-RAN C1-221735

x

TS 24.501



MCC list for 5GMM message C1-213895
New 5GMM cause for satellite access C1-213089
5QI for satellite access C1-212538
5GMM procedures for satellite access for reject cause on UE location – alternative handling C1-214891
UE's handling of the indication of country of UE location C1-213835
PDU session establishment for NR satellite access C1-213850
Validity of cause code #78 C1-217450
Multiple TACs from the lower layers C1-224099
Alignment to KI#2 conclusions on EPLMN list C1-216163
Addition of extended NAS timers via a satellite NG-RAN cell – Alternative A Details C1-222030

TS 24.571

CT3, CT4 TS

CT6 TS

Discussion

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