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EP-4736531-A1 - METHODS AND APPARATUSES FOR PERFORMING LAYER 1/LAYER 2 TRIGGERED MOBILITY

EP4736531A1EP 4736531 A1EP4736531 A1EP 4736531A1EP-4736531-A1

Abstract

Embodiments described herein relate to methods and apparatuses for enabling a user equipment to determine whether to perform a layer 2, L2, reset for a first layer 1/layer 2 triggered mobility, LTM, cell switch procedure from a source cell towards a target LTM candidate cell. A method performed by a user equipment comprises receiving at least an LTM candidate cell configuration for the target LTM candidate cell; obtaining a reset indication of whether an L2 reset procedure is to be performed for the first LTM cell switch procedure; obtaining an indication of an L2 reset group of the target LTM candidate cell; performing the first LTM cell switch procedure; and determining, based on the reset indication and the indication of the L2 reset group of the target LTM candidate cell, whether to perform an L2 reset.

Inventors

  • DA SILVA, Icaro Leonardo
  • WALLENTIN, PONTUS
  • ORSINO, Antonino
  • BERGQVIST, JENS
  • WAGER, STEFAN

Assignees

  • Telefonaktiebolaget LM Ericsson (publ)

Dates

Publication Date
20260506
Application Date
20240610

Claims (20)

  1. 1 . A method, performed by a user equipment, for determining whether to perform a layer 2, L2, reset for a first layer 1/layer 2 triggered mobility, LTM, cell switch procedure from a source cell towards a target LTM candidate cell, the method comprising: receiving (402) at least an LTM candidate cell configuration for the target LTM candidate cell; obtaining (404) a reset indication of whether an L2 reset procedure is to be performed for the first LTM cell switch procedure; obtaining an indication of an L2 reset group of the target LTM candidate cell; performing (406) the first LTM cell switch procedure; and determining (408), based on the reset indication and the indication of the L2 reset group of the target LTM candidate cell, whether to perform an L2 reset.
  2. 2. The method of claim 1 further comprising, responsive to determining to perform an L2 reset procedure, performing an L2 reset procedure.
  3. 3. The method of any previous claim further comprising performing the first LTM cell switch procedure in response to receiving an LTM cell switch command.
  4. 4. The method of any one of claims 1 to 3 wherein the reset indication comprises: an indication associating the source cell with a first L2 reset group of LTM candidate cells.
  5. 5. The method of claim 4 wherein the step of determining whether to perform an L2 reset comprises: responsive to the indication of the L2 reset group of the target LTM candidate cell indicating that the target LTM candidate cell belongs to the first L2 reset group of LTM candidate cells, determining not to perform an L2 reset.
  6. 6. The method of claim 4 or 5 wherein the step of determining whether to perform an L2 reset comprises: responsive to the indication of the L2 reset group of the target LTM candidate cell indicating that the target LTM candidate cell does not belong to the first L2 reset group of LTM candidate cells, determining to perform an L2 reset.
  7. 7. The method of any one of claim 1 to 6 wherein obtaining the reset indication comprises receiving the reset indication in a first LTM configuration.
  8. 8. The method of claim 7 wherein receiving the first LTM configuration before receiving the at least one LTM candidate cell configuration.
  9. 9. The method of any one of claims 7 to 8, further comprising receiving the first LTM configuration from a source network node providing the source cell or from a third network node via the source network node.
  10. 10. The method as in any one of claims 1 to 9 further comprising using the indication of the L2 reset group of the target LTM candidate cell as an indication of a L2 reset group of a new serving cell after the execution of the first LTM cell switch procedure.
  11. 11 . The method as in any one of claims 1 to 10, further comprising setting the value of the reset indication to the value of the indication of the L2 reset group of the target LTM candidate cell after performing the first LTM cell switch procedure.
  12. 12. The method as claimed in any one of claims 1 to 11 wherein the reset indication comprises a Itm-ServingCellNoResetID.
  13. 13. The method as claimed in any one of claim 1 to 12 wherein the L2 reset group of the target LTM candidate cell comprises an Itm-NoResetID.
  14. 14. A method in a source network node for enabling a user equipment, UE, to determine to perform a layer 2, L2, reset for a first layer 1/layer 2 triggered mobility, LTM, cell switch procedure from a source cell towards a target LTM candidate cell, comprising: transmitting (602), to the UE, at least an LTM candidate cell configuration for the target LTM candidate cell comprising an indication of an L2 reset group of the target LTM candidate cell; and transmitting (604), to the UE, a reset indication of whether a L2 reset is to be performed for the first LTM cell switch procedure.
  15. 15. The method as in claim 14 further comprising transmitting an LTM cell switch command to the UE in order to trigger the execution of the first LTM cell switch procedure.
  16. 16. The method as in claim 14 or 15 further comprising receiving from a third network node a first LTM configuration comprising the reset indication.
  17. 17. The method as in claim 14, further comprising receiving a request from the third network node to setup an LTM candidate cell configuration.
  18. 18. The method as in claim 14, further comprising receiving the first LTM configuration in the same signaling that requests source network node to configure an LTM candidate cell configuration at the UE.
  19. 19. The method as in claim 14 further comprising receiving the first LTM configuration responsive to transmitting a request for the first LTM configuration to the third network node.
  20. 20. The method as claimed in any one of claims 14 to 19 wherein the reset indication comprises a Itm-ServingCellNoResetID.

Description

METHODS AND APPARATUSES FOR PERFORMING LAYER 1/LAYER 2 TRIGGERED MOBILITY TECHNICAL FIELD Embodiments described herein relate to methods and apparatuses for determining whether to perform a layer 2 (L2) reset for a first Layer 1 (L1)/L2 triggered mobility, LTM cell switch procedure from a source cell to a target LTM candidate cell. BACKGROUND L1/L2 based inter-cell mobility in Rel-18 In 3GPP Release 18, a work item known as Further New Radio (NR) mobility enhancements is ongoing. This work item includes a technical area entitled Layer 1/Layer 2 (L1/L2) based inter-cell mobility. According to the Work Item Description, “when the UE moves from the coverage area of one cell to another cell, at some point a serving cell change needs to be performed. Currently serving cell change is triggered by L3 measurements and is done by RRC signaling triggered Reconfiguration with Synchronization for change of PCell and/or PSCell, as well as release add for SCells when applicable. All cases involve complete L2 (and L1) resets, leading to longer latency, larger overhead and longer interruption time compared to beam switch mobility (beam management procedures, TCI state activation). The goal of L1/L2 based inter-cell mobility is to enable a serving cell change via L1/L2 signaling, in order to reduce the latency, overhead and interruption time.” In this work item, the following is included as one objective of the work: 1. To specify mechanism and procedures of L1/L2 based inter-cell mobility for mobility latency reduction: o Configuration and maintenance for multiple candidate cells to allow fast application of configurations for candidate cells [RAN2, RAN3] o Dynamic switch mechanism among candidate serving cells (including SpCell and SCell) for the potential applicable scenarios based on L1/L2 signalling [RAN2, RAN1] o L1 enhancements for inter-cell beam management, including L1 measurement and reporting, and beam indication [RAN 1, RAN2] Note 1: Early RAN2 involvement is necessary, including the possibility of further clarifying the interaction between this bullet with the previous bullet o Timing Advance management [RAN 1, RAN2] o CU-DU interface signaling to support L1/L2 mobility, if needed [RAN 3] Note 2: FR2 specific enhancements are not precluded, if any. Note 3: The procedure of L1/L2 based inter-cell mobility are applicable to the following scenarios: □ Standalone, CA and NR-DC case with serving cell change within one CG □ Intra-DU case and intra-CU inter-DU case (applicable for Standalone and CA: no new RAN interfaces are expected) □ Both intra-frequency and inter-frequency □ Both FR1 and FR2 □ Source and target cells may be synchronized or non-synchronized In 3GPP, discussions have started regarding solutions for L1/L2 based inter-cell mobility (sometimes also referred to as LTM, L1/L2-triggered mobility or lower layer-triggered mobility). A basic principle with L1/L2-triggered mobility is that a user equipment (UE) may be preconfigured, by the network, with an RRC configuration per LTM candidate cell, sometimes also known as a LTM candidate cell configuration. Such a LTM candidate cell configuration may be comprised in an RRCReconfiguration message or one or more information elements (IEs)/ fields/ parameters such as CellGroupConfig. The UE may perform measurements on these LTM candidate cells and may transmit corresponding measurement reports to the network. The network then triggers the execution of a LTM cell switch procedure in the UE to one of these LTM candidate cells by transmitting lower layer signaling in a MAC CE, sometimes also referred to as an LTM cell switch command, to the UE, which then connects to the particular LTM candidate cell and switches to the LTM candidate cell configuration. The interactions between UE, CU, S-DU and C-DU may be summarized as in the latest version of the running CR for TS 38.401 a section quoted from R3-23349 is provided below for reference. Inter-qNB-DU LTM This procedure is used for the case when the UE moves from one gNB-DU to another gNB- DU within the same gNB-CU during NR operation for LTM. Figure 1 illustrates the inter-gNB- DU LTM procedure for intra-NR. Figure 1: inter gNB-DU LTM 1. The UE sends a MeasurementReport message (L3 measurement result FFS) to the source gNB-DU containing measurements of neighboring cells. The source gNB-DU sends an UL RRC MESSAGE TRANSFER message conveying the received MeasurementReport message to the gNB-CU. 2. The gNB-CU determines to initiate LTM configuration. 3. The gNB-CU sends a UE CONTEXT SETUP REQUEST message to the candidate gNB-DU, containing one target candidate cell ID. 4. If the candidate gNB-DU accepts the request of LTM configuration, it responds to the gNB-CU with a UE CONTEXT SETUP RESPONSE message including the generated lower layer RRC configuration for the accepted target candidate cell. 5. The gNB-CU sends a DL RRC MESSAGE TRANSFER message to the source gNB- DU, which includes the generated RRCReconfiguratio