R1-2601918
discussion
Discussion on beam management for 6GR downlink and uplink
From BeammWave AB
Summary
This document from BeammWave AB identifies key limitations in 5G-NR beam management based on deployment experience and provides 12 proposals for 6GR enhancements. The proposals focus on defining new SLS/LLS evaluation methodologies with latency and overhead metrics, evolving the TCI/QCL framework toward spatial-context-based indication, and studying mechanisms for faster beam measurement, UE-initiated reporting, and uplink beam management.
Position
BeammWave proposes defining new SLS and LLS evaluation methodologies with explicit metrics—beam acquisition latency (SSB detection to stable beam), beam application time (beam report to actual PDSCH/PUSCH usage), beam recovery time, and control signaling overhead ratio—arguing that conventional throughput and BLER-based assessments fail to capture deployment pain points. They propose evolving the unified TCI/QCL framework from 1:1 per-beam TCI states to spatial-context-based indication entities capable of 1:N associations with multiple reference signals, enabling UE-side beam selection within network-indicated spatial groups. They support capability-dependent CSI-RS configuration that adapts resource mapping based on UE beamforming capability and favors studying DMRS-based beam measurement alongside CSI-RS for reduced application time during active data transmission. They propose studying UE-initiated and event-driven beam management with lightweight uplink indication mechanisms to avoid multi-step MAC-CE/DCI signaling delays.
Key proposals
- Proposal 1 (Sec 2.2): Define SLS and LLS evaluation methodologies that explicitly capture beam management performance, including beam acquisition latency, beam application time, beam recovery time, and control signaling overhead metrics.
- Proposal 2 (Sec 2.2): Define UE antenna and TRXU modeling assumptions for SLS and LLS that reflect a range of UE beamforming capabilities, enabling fair comparison across different beam management approaches.
- Proposal 3 (Sec 2.2): Define beamforming assumptions for SLS and LLS evaluation that include a baseline beamforming scheme (e.g., DFT-based) while allowing companies to report results based on more advanced implementations (e.g., digital or hybrid beamforming).
- Proposal 4 (Sec 2.2): Define a common reference procedure for beam sweeping in SLS and LLS, while allowing companies to report detailed sweeping assumptions used for the evaluated beam management mechanism.
- Proposal 5 (Sec 2.3): Study capability-dependent CSI-RS configuration mechanisms where mapping of CSI-RS resources in time, frequency, and spatial domains is adapted based on UE beamforming capability.
- Proposal 6 (Sec 2.3): Study beam indication mechanisms that evolve the unified TCI/QCL framework beyond per-beam TCI states, including definition of QCL properties and QCL chains for group-based or spatial-context-based representations.
- Proposal 7 (Sec 2.4): Study mechanisms enabling a single spatial-context-based indication entity (e.g., carried in a DCI TCI field) to be associated with a set of reference signals and corresponding QCL behaviours.
- Proposal 8 (Sec 2.5): Study mechanisms that reduce the time required to evaluate candidate beams, including support for faster or parallel evaluation of multiple candidate beams and AI/ML-based beam prediction mechanisms.
- Proposal 9 (Sec 2.5): Study efficient and scalable beam reporting mechanisms, including grouped or compressed reporting and the ability to report multiple candidate beams or spatial contexts.
- Proposal 10 (Sec 2.5): Study UE-initiated and event-driven beam management mechanisms, associated reporting formats, lightweight uplink indication mechanisms, and corresponding network responses with the objective of reducing beam application time.
- Proposal 11 (Sec 2.5): Study the signaling framework for beam measurement, reporting, and indication, including support for spatial-context-based information exchange across layers and the role of uplink beam measurement.
- Proposal 12 (Sec 2.5): Study a framework for uplink beam management based on spatial-context-based indication, including UE transmit beam selection and aNB receive beam determination within a network-indicated spatial context.