DL Synchronization and TCI State Activation Discussion
Discussing DL synchronization including TCI state activation with scenarios for beam indication timing, unified TCI framework, and reducing handover delay for Rel-18 LTM. Different procedures for DL synchronization and TCI state activation are explored, highlighting the importance of understanding activated TCI states for candidate cells. The need for a common understanding between serving and candidate DUs is emphasized.
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AI9.12.1 Offline discussion (Wed)
Agenda DL synchronization (including TCI state activation) 5.3.3-1c and 5.5.2 L1 measurement report LS
DL Synchronization - background [Conclusion at RAN1#111] Agreement - For beam indication timing for Rel-18 LTM, - Support Scenario 2: Beam indication together with cell switch command, - For Rel-17 unified TCI framework, - Beam indication indicates TCI state for each target serving cell - FFS: Scenario 1: Beam indication before cell switch command - FFS: Scenario 3: Beam indication after cell switch command - FFS: Activation of TCI state(s) of target serving and/or candidate cell(s). [Conclusion at RAN1#111] Agreement Regarding the potential RAN1 enhancements to reduce the handover delay / interruption for Rel- 18 LTM - Support at least DL synchronization for candidate cell(s) based on at least SSB before cell switch command - Further study mechanism, e.g. capability the necessary and signaling UE Problem: It is not clear if these descriptions with yellow shadow are the same thing. Do companies have the same understanding?
DL Synchronization Question 1 Alt.1 Two-step DL synchronization procedure UE maintains DL synchronization with SSB after L1 measurement and then gNB activates TCI state(s), and then the UE starts DL synchronization with the QCL source of the TCI states Alt.2-1 One-step DL synchronization procedure UE maintains DL synchronization with SSB after L1 measurement Alt.2-2 One-step DL synchronization procedure gNB activates TCI state(s), and then UE starts DL synchronization with the QCL source of the TCI states activate includes - activation before cell switch command, if agreed - activation together with beam indication included in cell switch command
DL synchronization Way forward?? - Keep the separate discussion on TCI state activation and DL sync - For scenario 2, TCI state activation procedure is introduced, which is performed before beam indication based on Rel-17 unified TCI framework included in MAC CE conveying cell switch command. - [UE performs the DL synchronization with the QCL source RS for the activated TCS state(s)] - TCI state activation is supported for candidate cells including intra- and inter- frequency - It is assumed that the serving DU and candidate/target DU have a common understanding on the activated and indicated TCI state(s) for a UE, detailed procedure/mechanism is up to RAN3/RAN2 - The TCI state indicated in the beam indication is selected from the activated TCI states
L1 measurement reporting [FL proposal 5-2-1-v3] - For L1 measurement reporting for LTM, - At maximum [4] beams (4 is a starting point, FFS: the values and UE capabilities) from candidate cell(s) [and serving cells] configured for measurement & reporting can be reported in a single report instance - FFS whether the configured candidate cell(s) can be activated - FFS how to choose the beams to be reported from multiple candidate cells, e.g. from all configured/activated candidate cells, from each candidate cell, from each group of candidate cells, from selected candidate cells, one beam from serving cell is always chosen - [Additionally/At least]1 beam from the serving cell is included in the report instance - FFS: always included or depending on the gNB configuration FL note: RRC configuration is not the scope of this proposal
LS Send an LS to RAN2,3,4 on the RAN1 agreements in this meeting All agreements in AI 9.12.1 and 9.12.2 in RAN1#112 are included The LS contents agreed in AI 9.12.1 (on L1 measurement configuration) and AI 9.12.2 (on RAR) are also included
