4.13 Introduction of satellite support for Cellular IoT

23.4013GPPGeneral Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) accessRelease 18TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

4.13.1 General

This clause describes the functionality for supporting Cellular IoT over satellite access. Support for WB-E-UTRAN, NB-IoT and LTE-M satellite access is specified in TS 36.300 [5].

4.13.2 Support of RAT types defined in EPC for satellite access

In the case of satellite access with WB-E-UTRAN, NB-IoT or LTE-M, the RAT Types values "WB-E-UTRAN(LEO)", "WB-E-UTRAN(MEO)", " WB-E-UTRAN(GEO)", " WB-E-UTRAN(OTHERSAT)", "NB-IoT(LEO)", "NB-IoT(MEO)", "NB-IoT(GEO)", "NB-IoT(OTHERSAT)", "LTE-M(LEO)", "LTE-M(MEO)", "LTE-M(GEO)" and "LTE-M(OTHERSAT)" are used in EPC to distinguish the different WB-E-UTRAN, NB-IoT and LTE-M satellite access types.

In order to enable efficient enforcement of mobility restrictions:

– Cells of each NB-IoT satellite RAT type (NB-IoT(LEO), NB-IoT(MEO), NB-IoT(GEO) or NB-IoT(OTHERSAT)) need to be deployed in TAs that are:

– different from TAs for other NB-IoT satellite RAT types; and

– different from TAs supporting terrestrial NB-IoT RAT type; and

– different from TAs for WB-E-UTRAN satellite RAT types; and

– different from TAs for WB-E-UTRAN terrestrial RAT types.

The MME may initiate Detach of the UE when an S1 UE Context Release Request is received with Cause indicating the release is requested due to a UE using satellite access moved out of PLMN serving area, as specified in TS 36.413 [36].

4.13.3 Network/Access selection for satellite access

Network/Access selection principles specified in clause 4.3.2.2 also apply for satellite access for Cellular IoT.

In the case of satellite access for Cellular IoT, a UE with location capability (i.e. GNSS capability) should use its awareness of its location to select a PLMN that is allowed to operate the UE location as specified in TS 23.122 [10].

In order to ensure that regulatory requirements are met, the network may be configured to enforce this UE choice by verifying the UE location as specified in clause 4.13.4.

4.13.4 Verification of UE location

In order to ensure that the regulatory requirements are met, the network may be configured to enforce that the selected PLMN is allowed to operate in the current UE location by verifying the UE location during EMM and ESM procedures. In this case, when the MME receives the User Location Information (ULI) for a UE using satellite access for Cellular IoT, the MME may decide to verify the UE location.

If the MME determines based on the Selected PLMN ID and the identity of the cell serving this UE that it is not allowed to operate at the present UE location the MME should reject any NAS request with a suitable Cause value. If the UE is already registered to the network when the MME determines that the UE is not allowed to operate at the present UE location, the MME may initiate an explicit detach of the UE. The MME should not reject the request or detach the UE unless it has sufficiently accurate UE location information to determine that the UE is located in a geographical area where the PLMN is not allowed to operate.

NOTE: The area where the PLMN is allowed to operate can be determined based on local regulations and licensing conditions.

If the MME is not able to determine the UE location with sufficient accuracy to make a decision or if the received ULI is not sufficiently reliable, the MME proceeds with the Mobility Management or Session Management procedure and may initiate UE location procedure after the Mobility Management or Session Management procedure is complete, as specified in clause 9.1.17 of TS 23.271 [57], to determine the UE location. The MME shall be prepared to detach the UE if the information received from the E SMLC indicates that the UE is registered to a PLMN that is not allowed to operate in the UE location. In case of a NAS procedure, the MME should either reject any NAS request targeted towards a PLMN that is not allowed to operate in the known UE location and indicate a suitable cause value, or accept the NAS procedure and initiate the Detach procedure once the UE location is known. In the Detach Request message to the UE, the MME shall include a suitable cause value.

4.13.5 Use of extended NAS timers

Whenever the UE is accessing the network using a satellite RAT, the MME shall set the NAS timers long enough according to the worst transmission delay (see TS 24.301 [46]). For a UE accessing the network using satellite WB-E-UTRAN(GEO) RAT regardless whether CE mode B is used or not for this UE, the MME shall use the extended NAS timer settings for the UE as specified in TS 24.301 [46].

Editor’s note: The above text is FFS and to be aligned accordingly following CT WG1 discussions.

4.13.6 Support of Tracking Area Update

A moving cell for NB-IoT, LTE-M or WB-E-UTRAN satellite access may indicate support for one or more Tracking Areas Codes (TACs) for each PLMN (see clause 4.13.7). A UE that is registered with a PLMN may access a cell and does not need to perform a Tracking Area Update procedure for mobility reasons as long as at least one supported TAC for the RPLMN or equivalent to the RPLMN indicated in the cell is part of the UE’s Tracking Area List. A UE shall perform a Tracking Area Update procedure when entering a cell where none of the supported TACs for the RPLMN or equivalent to the RPLMN indicated in the cell are part of the UE’s Tracking Area List.

When indicating a last visited TAI in an Attach Request or a TAU Request, a UE may indicate any TAI supported in the last visited cell for that RPLMN or PLMN equivalent to the RPLMN.

4.13.7 Tracking Area handling

For Cellular IoT over satellite access with moving cells, in order to ensure that each TA is Earth-stationary, even if the radio cells are moving across the Earth’s surface, the E-UTRAN may change the TAC values that are broadcast in a cell’s system information as the cell moves, as described in TS 36.331 [37].

E-UTRAN may broadcast in a cell a single TAC per PLMN and change this TAC value as the cell moves. Alternatively, the E-UTRAN may broadcast in a cell more than one TAC for a PLMN and add or remove TAC values as the cell moves. The eNodeB provides either the single broadcast TAI or all broadcast TAIs corresponding to the Selected PLMN as described in TS 36.413 [36] to the MME as part of the ULI, whenever the TAI is included in the S1-AP message as described in TS 36.413 [36]. The eNodeB indicates, if known, also the TAI where the UE is geographically located.

NOTE: The MME can take into account the TAI where the UE is geographically located, and the last visited TAI to generate a suitable Tracking Area List for the UE.

The MME considers the UE to be in a forbidden area if the only TAI or all TAIs received from the eNodeB are forbidden based on subscription data. The UE considers it is in a cell within a forbidden area if the only TAI or all TAIs broadcast in this cell for the selected PLMN are forbidden. In a PLMN, the UE considers it is not in a cell within a forbidden area if at least one broadcast TAI for this PLMN in this cell is not forbidden.

If the MME receives multiple TAIs from E-UTRAN and determines that some, but not all, TAIs in the received list of TAIs are forbidden by subscription or by operator policy, the MME shall send the forbidden TAI(s) to UE as described in clause 5.3.2, 5.3.3 and 5.3.4. The UE stores the TAI(s) in the appropriate Forbidden Area list and removes the TAI(s) from the TAI list.