Content for  TS 23.501  Word version:  19.1.0

Mobile gNB with Wireless Access Backhauling (MWAB) provides an NR access link to UEs in proximity and connects to the 5GC serving the UE through an IP connectivity provided by a Backhaul PDU session(s), as illustrated in Figure 5.49.1.1-1. The MWAB consists of a gNB component (MWAB-gNB) and a UE component (MWAB-UE). The MWAB-gNB is based on the gNB functionality specified in TS 38.300 and TS 38.401. The MWAB may be mounted on a moving vehicle and may serve UEs inside or outside the vehicle. The MWAB-UE establishes the IP connectivity for the backhaul links for the MWAB-gNB, via NR Uu, using the existing registration procedure and PDU session establishment procedure. The backhaul links are between the MWAB-gNB and entities of the network (e.g. AMF, UPF, other gNBs and OAM server) that a MWAB-gNB cell serves. The IP connectivity provided by the MWAB-UE may be either via the same PLMN/SNPN that the MWAB-gNB serves or a different PLMN/SNPN, depends on the MWAB-UE PLMN selection mechanism as specified in TS 23.122. Different possible deployment scenarios are presented in Annex S. MWAB operation supports both PLMN and SNPN cases. When the MWAB-gNB is serving a PLMN, the UEs served by MWAB may be non-roaming or roaming in the MWAB Broadcasted PLMN. In case the MWAB-gNB is serving a SNPN, the subscribed SNPN of the UEs may be different from the MWAB Announced SNPN. The UEs served by the MWAB are not aware of the network serving the MWAB-UE.

MWAB-UE has a single NR Uu hop to the NG-RAN, using either TN or NTN access technology. NR access is used for the radio link between a MWAB-gNB and the served UEs. The NR Uu access link between the MWAB-gNB and the served UE(s) does not use NTN access technology. 5G MOCN can be supported by the MWAB-gNB. The details of the MWAB configuration/provisioning process are described in clause 5.49.2. In order to operate as MWAB, the MWAB-gNB component and MWAB-UE component are authorized and controlled separately. The detailed procedures for the authorization of MWAB are described in clause 5.49.3. Service continuity for the UE(s) served by the MWAB-gNB is supported, when the MWAB moves and the UE(s) move or do not move together with the MWAB. The detailed procedures for the support of mobility are described in clause 5.49.5. The MWAB shall be able to serve UE(s) without any MWAB-specific enhancements. For some operations, the MWAB may be configured to provide access to only certain UEs. Existing access control mechanisms, e.g. CAG control, can be used to manage the UE(s)'s access to the MWAB-gNB. The details of the access control of the UEs served by MWAB are described in clause 5.49.6. The LCS framework as defined in TS 23.273 is used for providing the location service to the UE(s) served by MWAB. Details on supporting the LCS over MWAB are described in clause 5.49.7. Regulatory services (e.g. emergency services, priority services) can be supported by the MWAB, and the details are provided in clause 5.49.8.

The MWAB-UE manages the BH PDU Session(s) for the MWAB operation based on the configuration by the HPLMN or Subscribed SNPN of the MWAB-UE. The configuration of the MWAB-UE can be UE Local Configuration, or URSP rules as defined in TS 23.503, for the determination of the proper PDU session parameters, e.g. the DNN, S-NSSAI, the SSC Mode, etc. The URSP rules can be preconfigured or provisioned to the MWAB-UE by its HPLMN using UE Policy delivery as described in clause 4.2.4.3 of TS 23.502.

The MWAB-gNB's configuration is managed by the OAM of the MWAB Broadcasted PLMN/SNPN, and the address (or FQDN) of the OAM server per MWAB Broadcasted PLMN/SNPN may be configured at the MWAB-gNB. The OAM server of the MWAB Broadcasted PLMN/SNPN provides configuration parameters e.g. for the purpose including the access stratum operation of the MWAB-gNB, the N2, N3 and Xn interface management, activating/deactivating the MWAB-gNB operation, and to assist the MWAB-gNB providing information used by MWAB-UE for the BH PDU Session(s) management via URSP processing.

The existing UE mobility procedures without MWAB-specific UE enhancements can be reused to handle a UE mobility to and from a MWAB-gNB while the UE is in CM-IDLE or CM-CONNECTED modes, irrespective of whether the MWAB is static or the MWAB is moving, i.e.:

• For UEs in RRC_IDLE and RRC_INACTIVE state procedure for cell (re ) selection as specified in TS 38.304 and TS 23.122 for RRC_IDLE and RRC_INACTIVE is used as normal irrespective of cells are belonging to a MWAB-gNB or a gNB.
• For UEs in RRC_CONNECTED state, the MWAB-gNB or gNB triggers the handover procedures to the neighbouring cells (irrespective of whether they are belonging to a MWAB-gNB or a gNB) for UEs in RRC_CONNECTED state.

UEs and MWAB-gNB use existing procedures as specified in clause 8.23 of TS 38.401, TS 23.502, or TS 38.304.

For a UE served by an MWAB-gNB cell, the MWAB-gNB may trigger the handover procedures for UEs in CM-CONNECTED mode as specified in TS 38.401.

The mobility of MWAB includes the MWAB-UE and the MWAB-gNB aspect.

• The mobility of the MWAB-UE reuses the exiting UE mobility procedures specified for normal UE.
• The MWAB-gNB can obtain a new configuration from OAM server of MWAB Broadcasted PLMN during mobility.
• The MWAB-UE may request new or modify existing BH PDU Sessions for the corresponding N2, N3 and Xn interfaces, upon request from the MWAB-gNB as it moves in the network and the MWAB-gNB updates the TNL association as specified in clause 5.21.1 and TS 38.401 to use the new TNL information associated with the new BH PDU Session(s) as needed.
• SSC mode 3 may be applied to the BH PDU Sessions to minimize traffic interruption when UPF re-allocation for these BH PDU Sessions is required during the MWAB mobility.
• When it is required to change AMF for the UEs served by the MWAB-gNB upon mobility of a MWAB into a new region, the TAC(s) and Cell ID(s) the MWAB-gNB announces also change.