5.4.8 Support for identification and restriction of using unlicensed spectrum

Support for NG-RAN using unlicensed spectrum is defined in TS 38.300 [27] and TS 36.300 [30].

For NG-RAN, in the case of NR in stand-alone mode, all cells are in unlicensed spectrum and the NR is used as primary RAT. NR or E-UTRA cells in unlicensed spectrum, can be used as secondary cells as specified in the Dual Connectivity architecture defined in clause 5.11 or in addition can be configured to support the Carrier Aggregation Architecture (CA) defined in TS 38.300 [27] and TS 36.300 [30].

For either case the serving PLMN can enforce Access Restriction for Unlicensed Spectrum (either signalled from the UDM, or, locally generated by VPLMN policy in the AMF) with the following:

• To restrict the use of NR in unlicensed spectrum as primary RAT, the AMF rejects the UE Registration procedure with appropriate cause code defined in TS 24.501 [47] if the UE performs initial access from NR using unlicensed spectrum. If the UE is accessing through some other allowed RAT, the AMF signals this access restriction to NG-RAN as part of Mobility Restriction List.
• To restrict the use of use of unlicensed spectrum with NR or E-UTRA as secondary RAT using Dual Connectivity or Carrier Aggregation Architecture (CA) defined in TS 38.300 [27] and TS 36.300 [30], the AMF signals this access restriction to NG-RAN as part of Mobility Restriction List.

An NG-RAN node supporting aggregation with unlicensed spectrum using either NR or E-UTRA checks whether the UE is allowed to use unlicensed spectrum based on received Mobility Restriction List. If the UE is not allowed to use Unlicensed Spectrum, the NG-RAN node shall restrict the using of unlicensed spectrum, either NR or E-UTRA as secondary RATs when using either Dual Connectivity or Carrier Aggregation (CA) as defined in TS 38.300 [27] and TS 36.300 [30].

At inter-RAT handover from E-UTRAN/EPS, the Access Restriction for Unlicensed Spectrum is either already in the AMF's UE context, or is obtained from the UDM during the subsequent Registration Area Update procedure (i.e. not from the source MME or source RAN). In both inter-RAT handover cases, any Access Restriction for use of Unlicensed Spectrum is then signalled to NG-RAN or enforced in AMF.

NOTE: This signalling of the Access Restriction during the Registration Area Update after the inter-RAT handover procedure means that there is a small risk that unlicensed spectrum resources are transiently allocated.

When the UE is accessing 5GS using unlicensed spectrum as primary RAT:

• The NG-RAN node shall provide an indication to the AMF in N2 interface that NR access is using unlicensed spectrum as defined in TS 38.413 [34].
• In order to restrict access to NR in unlicensed spectrum, cells supporting NR in unlicensed spectrum have to be deployed in Tracking Area(s) different to cells supporting licensed spectrum.
• When the AMF receives an indication from NG-RAN over N2 whether NR in unlicensed spectrum is being used as defined in TS 38.413 [34], the AMF provides to the SMF an indication that the RAT type is NR with usage of unlicensed spectrum during PDU Session Establishment or as part of the UP activation and Handover procedures.
• The PCF can also receive the indication whether the UE is using NR in unlicensed spectrum, when applicable, from the AMF using the PCRT on Access Type change specified in clause 6.1.2.5 of TS 23.503 [45] during AM Policy Association Establishment or AM Policy Association Modification procedure and from the SMF using the PCRT on Access Type change specified in clause 6.1.3.5 of TS 23.503 [45] during SM Policy Association Establishment or SM Policy Association Modification procedure.
• The NFs generating CDRs shall include the indication that the UE is using NR in unlicensed spectrum in their CDRs.

When the UE is accessing NR or E-UTRA using unlicensed spectrum as secondary RAT, procedures for Usage Data Reporting for Secondary RAT as defined in clause 5.12.2 can apply.