R1-2601838
discussion
On beam management for downlink and uplink in 6GR
From Nokia
Nokia's prior position on
10.5.2.4
at
RAN1#124
· AI-synthesized, paraphrased
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Proposes that NR Release-17 unified TCI framework principles serve as the 6G baseline while studying enhancements to address identified limitations including the limited number of indicated TCI states, reliance on periodic TRS as QCL source RS, and lack of TCI-state specific physical-layer parameter configuration. Proposes a unified design for UE-initiated L1 measurement reporting framework across beam management and beam-based cell switch procedures, citing fragmentation between RAN1-led UEIBR (UCI-based) and RAN2-led LTM event-triggered reporting (MAC CE-based) as a key lesson from 5G NR. Argues that the term beam is non-descriptive and potentially misleading for specifications and should be replaced with procedures reflecting the involved reference signals. Proposes studying CBRA-based BFR with MAC CE signaling as the baseline while also studying streamlined CFRA-based BFR and UL beam failure recovery within a unified TCI state framework. Presents simulation results for inter-cell beam prediction showing Top-1 beam ID accuracy exceeding 90% and Top-2 approaching 99%, and proposes studying cross-frequency beam prediction using one-sided AI/ML models for collocated deployments predicting beams across different component carriers within the same frequency range.
Summary
Nokia's Tdoc R1-2601838 proposes a comprehensive study for 6G Radio Layer 1 beam management, presenting 21 proposals and 16 observations. The document addresses the QCL/TCI framework, downlink and uplink beam measurement/reporting with AI/ML enhancements, beam indication, beam failure recovery, and evaluation methodology.
Position
Nokia proposes a unified 6GR beam management framework based on 5G NR Rel-17 unified TCI principles, while studying enhancements to address identified limitations. They propose studying a more flexible QCL parameterization that allows per-RS configuration of channel properties instead of fixed QCL types, and reducing reliance on periodic TRS as the main QCL source to improve energy efficiency. For AI/ML beam prediction, they position 5G NR Rel-19 spatial domain (BM-case1) and temporal domain (BM-case2) DL Tx beam prediction as the starting point, and propose direct extensions for inter-cell/multi-TRP and cross-frequency beam prediction. They propose studying UE-initiated beam reporting based on 5G NR Rel-19 Event-2 and Event-7, and studying BFR-type signaling as a fallback mechanism, with CBRA-based BFR using MAC CE signaling as the baseline. For evaluation, they provide simulation results showing inter-cell beam prediction achieving over 90% Top-1 beam ID accuracy and cross-frequency beam prediction achieving 2-3 dB mean RSRP error for UEs below -80 dBm.
Key proposals
- Proposal 1 (Sec 2.1): Study the QCL framework for 6GR, including QCL properties and QCL relationships/chains between source and target channel(s)/RS(s), with the objective of supporting UE mobility for different deployment scenarios, and improved energy efficiency.
- Proposal 3 (Sec 2.2): Support a unified beam measurement and reporting framework in 6GR that avoids fragmented designs for single-TRP and multi-TRP operation and supports both intra-cell and inter-cell BM scenarios, using both AI/ML and non-AI/ML based mechanisms.
- Proposal 8 (Sec 2.2.1): Study UE-initiated beam reporting when multiple TCI states are indicated for the UE for the serving cell.
- Proposal 10 (Sec 2.2.2): RAN1 to study inter-cell/multi-TRP DL Tx beam prediction as an extension of 5G NR AI/ML beam prediction by considering measurements from Set B of one or more TRPs/cells as input to an AI/ML model to predict best beam information and/or predicted measurements from Set A of target cell/TRP(s) of the current or a future time instance.
- Proposal 13 (Sec 2.3): Study beam correspondence assumptions and capabilities for UL beam management in 6GR.
- Proposal 16 (Sec 2.4): Study the components of beam indication mechanisms for 6GR BM, applicable to both UE-initiated/event driven and network-initiated BM, including: Configuration of TCI states; Definition of source and target RSs/channels for a TCI state; TCI state switching mechanism, e.g., TCI state activation and indication (for intra and inter-cell).
- Proposal 17 (Sec 2.4): Study beam indication for predicted beams within the unified TCI framework considering reducing the application time for predicted beams in addition to enhance the indication of multiple TCI states corresponding to future time instances.
- Proposal 18 (Sec 2.5): Study CBRA based BFR, with MAC CE based signaling as the baseline solution for 6GR BFR within a unified TCI state framework.
- Proposal 20 (Sec 2.5): Study UL beam failure recovery for 6GR.
- Proposal 21 (Sec 2.6): Adopt Table 1 for EVM Assumptions for 6GR BM SLS.