R1-2601867
discussion
Discussion on beam management for downlink and uplink
From ZTE
Summary
This ZTE contribution for the 6G Radio study item proposes a cell-cluster-based beam management framework for 6GR to support multi-TRP/cell-free operations from Day-1. The document contains 7 observations analyzing 5G design shortcomings and 33 detailed proposals covering beam measurement/report, QCL and beam indication, and unified UE-initiated beam management procedures.
Position
ZTE proposes adopting cell-cluster-based beam management as the foundational 6GR framework, defining TRP groups of up to 12-20 within a cluster for multi-TRP/cell-free Day-1 operation. They observe that 5G's overly complicated QCL-chain design including TRS proves commercially impractical and wastes time-frequency resources, proposing simplified QCL chains that remove TRS or replace it with DMRS. They require studying both AI/ML and non-AI compressed-sensing based beam prediction methods, presenting simulation results showing multi-TRP collaborative DNN+attention models achieve higher spatial domain prediction accuracy than single-TRP models. ZTE proposes studying UE antenna port-specific beam reporting under the R19 UT antenna model, noting RSRP differences between ports reach approximately 30 dB versus 10 dB in legacy modeling, making port-selection-based transmission preferable for handheld UTs. They propose a unified UE-initiated BM framework covering BFR, UEI beam reporting, and beam/TRP/cell switching, preferring UCI-based reporting with flexible payload size and optional association between UL transmission and NW response.
Key proposals
- Proposal 1 (Sec 2): For 6G Day-1 cell-free/multi-TRP, cell-cluster-based beam management with inter/intra-cluster beam measurement/report and QCL/indication procedures shall be supported.
- Proposal 2 (Sec 3.2): 6G beam measurement and reporting should natively support CSI-RS/SSB-based DL measurement with multi-TRP extensions, SRS-based UL measurement with multi-UE panel extensions, and P/SP/AP reporting of L1-RSRP/L1-SINR with CRI/SSBRI.
- Proposal 4 (Sec 3.3): Study early sync/CSI for multi-TRP during initial access, e.g., RSRP measurement and report for mTRP before Msg4.
- Proposal 5 (Sec 3.4): Study beam measurement and reporting with regards to UE antenna port-specific beam reporting to facilitate transmission schemes with UT antenna modelling.
- Proposal 7 (Sec 3.5.1): Consider native AI/ML based beam management methods for 6GR in diverse frequency bands, including spatial and temporal beam prediction.
- Proposal 9 (Sec 3.5.2): Study non-AI-based/advanced beam prediction such as compressed-sensing based solutions in 6GR for overhead and latency reduction.
- Proposal 11 (Sec 3.5.3): Study spatial/temporal domain beam prediction for mTRP/cell-cluster and frequency domain beam prediction at least for co-located scenarios, prioritizing intra-frequency-range inter-band.
- Proposal 18 (Sec 3.6): Study measurement and reporting mechanism for cell-cluster in 6GR.
- Proposal 22 (Sec 4.2): Study simplified QCL chains for 6G beam indication, e.g., by removing TRS or replacing it with DMRS to cut down on the base station's setup work and transmission overhead.
- Proposal 24 (Sec 4.3): Study unified TCI framework involving both joint and separate-DL/UL TCI state(s) for mTRP with consideration of sTRP as a special case, using hierarchical RRC+MAC CE+DCI structure.
- Proposal 27 (Sec 4.4): Study intra-cell cluster inter-TRP beam management in 6GR, e.g., inter-TRP switching performed by L1-level beam switching based on unified TCI framework.
- Proposal 29 (Sec 4.4): Study inter-cell cluster handover in 6GR by taking NR LTM as a starting point, including TCI state indications in cell-cluster switching command signaling.
- Proposal 30 (Sec 5.1): Strive to design a unified procedure framework of UE-initiated BM to accommodate different purposes (BFR, UEI/EDBR, RLF) and scenarios (sTRP or mTRP/cell-free) in 6GR.
- Proposal 31 (Sec 5.2.1): Study identifications of RSs for BFD/BFR for new scenarios like intra-cell or intra-cell cluster with counter-based triggering and UCI-based UL transmission.
- Proposal 33 (Sec 5.2.3): Study temporal domain beam prediction-based beam switching and beam failure recovery with reduced latency.