R1-2601857
discussion
Discussion on synchronization acquisition and beam measurement during initial access
From NEC
Summary
NEC's contribution proposes 20 specific study items for 6G Radio synchronization and initial access, focusing on SSB structure/periodicity, clustered common signaling, diverse device support, multi-TRP operation, and AI/ML-based beam management. The document provides detailed technical options across four main discussion areas.
Position
NEC proposes studying two concrete SSB bandwidth options (20 PRBs and 12 PRBs) to address 3MHz minimum spectrum allocation while managing sync raster sparsity and cell search complexity. They propose SSB periodicity extension to 80ms/160ms as a starting point, with mandatory support for SSB repetition in clusters using either consecutive or interleaved intra-cluster patterns. NEC requires PSS placement at the very beginning of the SSB block with SSS evenly distributed among PBCHs at a certain distance from PSS, maintaining NR's frequency offset estimation logic. They propose extending Rel-19 NES on-demand common signaling from SCell to PCell/isolated cell, specifically to utilize on-demand SSB transmissions for enhancing RLM, BFD, and Layer 3 mobility/handover measurements during extended periodicity gaps. NEC supports non-transparent multi-TRP schemes for early CSI acquisition and proposes studying AI/ML-based SSB prediction with RO selection using both UE-sided model inference (predicting ROs not associated with measured SSBs) and NW-sided model inference (via Msg1 repetition or Msg3 reporting).
Key proposals
- Proposal 1 (Sec 2.1.1): For 6GR SSB frequency bandwidth, study two options: 20 PRBs (same as NR) or 12 PRBs (smaller than NR, considering 3MHz minimum spectrum allocation).
- Proposal 2 (Sec 2.1.1): For 6GR SSB time-domain structure, study 4-symbol (same as NR) or 14-symbol (whole slot) options, with PSS at beginning and SSS distributed among PBCHs.
- Proposal 6 (Sec 2.1.2.1): Set UE default SSB periodicity assumption to 80ms or 160ms as starting point for 6GR, increased from NR's 20ms.
- Proposal 8 (Sec 2.1.2.2): Study SSB repetition in a cluster when long SSB periodicity is configured to reduce cell search latency.
- Proposal 10 (Sec 2.2.1): Study which channels/signals (SSB, SIB1, OSI, paging, random access) can be common or dedicated for diverse device types during initial access.
- Proposal 11 (Sec 2.2.1): Study two SIB1 options: separate SIB1s for eMBB and IoT devices, or one common SIB1 plus dedicated SIB1 for one device type.
- Proposal 12 (Sec 2.2.2): Extend Rel-19 NES on-demand common signaling from SCell/NES Cell to PCell or isolated cell for on-demand SSB/SIB1 transmission.
- Proposal 14 (Sec 2.2.3): Study ensuring PDCCH/PDSCH for SIB1 is adjacent and right after corresponding SSB transmission within one SSB periodicity.
- Proposal 15 (Sec 2.2.3): Study PF/PO configuration to minimize gap between first PO and last transmitted SSB in clustered common signal transmission.
- Proposal 17 (Sec 2.3): Study supporting early multi-TRP framework during initial access as a Day 1 6G feature.
- Proposal 18 (Sec 2.3): Study non-transparent TRP schemes for early CSI acquisition and beam management during initial access when UE enters RRC CONNECTED mode.
- Proposal 19 (Sec 2.3): Study AI/ML-based SSB and RO selection during initial access, considering both UE-sided and NW-sided model inference.
- Proposal 20 (Sec 2.4): Study AI/ML-based beam prediction for inter-cell beam management in mobility scenarios including LTM.