R1-2601807
discussion
Discussion on synchronization acquisition and beam measurement
From Spreadtrum
Spreadtrum's prior position on
10.5.1.1
at
RAN1#124
· AI-synthesized, paraphrased
verify sources →
Proposes that NR initial access procedures serve as the baseline for 6GR design with specific evolutionary enhancements. Argues that reducing 6GR sync signal bandwidth by a small margin does not significantly reduce sync raster entries but seriously degrades SSB receiving performance, and presents evaluation results showing only 6% additional NES gain when extending SSB periodicity from 40ms to 80ms under zero load. Requires same SCS between 6GR PSS/SSS and other channels/signals (except PRACH) for a given band across all frequency ranges, opposing different SCS for SSB versus other channels in FR2-1. Proposes studying beam prediction for initial access (Sub-use case D) leveraging AI/ML experience from NR BM-Case 1 for both SSB spatial prediction (Set B subset of Set A) and beam refinement prediction (Set B different from Set A). Supports introducing cell DTX/DRX operation in idle state and on-demand sync signals for both single-cell and multi-cell deployments, with NR SSB-less solutions as starting points for sync signal-less operation.
Summary
Spreadtrum (UNISOC) presents 43 proposals and 8 observations on 6GR synchronization acquisition and beam measurement, advocating a conservative evolutionary approach that largely inherits NR's initial access procedures, SSB structure, and signaling while selectively enhancing energy efficiency, coverage, and beam management.
Position
Spreadtrum proposes that 6GR initial access design should inherit NR's fundamental procedures, SSB structure (20 PRBs, 4 OFDM symbols), and PSS/SSS/PBCH architecture as the baseline, with a default SSB periodicity of 40ms for initial access to balance UE experience and network energy saving—citing that extending to 80ms yields only 6% additional energy-saving gain under zero load. They require a single unified SSB structure applicable across all deployment scenarios (single/multi-cell, multi-TRP, TN/NTN, all frequency ranges) and oppose introducing different SCS for SSB versus other channels/signals for a given band across all frequency ranges. They propose studying SSB repetition within one SSB period via three options (within burst set, burst set repetition, or combination) and require that at least two SSBs be mappable to one slot of 14 symbols. For on-demand sync signals, they propose further identifying valid scenarios for both network-triggered and UE-triggered mechanisms under standalone (DS#1b, DS#1c) and multi-cell/carrier (DS#2a, DS#2b) deployments, while supporting on-demand SSB for SCell in Day1 and sync signal-less operation for SCell using NR solutions. They require studying AI-based beam prediction for initial access (Sub-use case D) leveraging NR BM-case 1 experience for both SSB spatial prediction and beam refinement prediction, and propose studying enhanced cell DTX/DRX operation in both RRC connected and idle states.
Key proposals
- Proposal 1 (Sec 2): NR initial access procedure should be a starting point for 6GR initial access design.
- Proposal 2 (Sec 3): A single unified SSB structure design needs to be defined to meet all supported deployment scenarios including single and multiple cells/carriers/TRPs/beams, frequency ranges, and TN and NTN.
- Proposal 4 (Sec 3.1.1): In order to balance UE experience and network energy-saving requirements, 40ms SSB periodicity for initial access can be a starting point.
- Proposal 8 (Sec 3.1.3): For 6GR SSB structure design, NR SSB can be as a starting point, preferring 20 PRB bandwidth and 4 OFDM symbols.
- Proposal 14 (Sec 3.3): For 6GR, at least two initial synchronization signal types, i.e., 6GR primary SS and 6GR secondary SS, are supported, with PSS used for initial symbol boundary synchronization and partial cell ID detection.
- Proposal 17 (Sec 3.3): For 6GR PSS/SSS design, at least target detection performance/latency/complexity, supported PCI number, minimum spectrum allocation, and other identified functionalities carried by PSS/SSS should be considered.
- Proposal 19 (Sec 3.4): At least SFN, half-frame-index (if necessary), SSB index, SSB subcarrier offset, RMSI PDCCH configuration, and DL DMRS position should be carried by 6GR PBCH.
- Proposal 22 (Sec 3.6): The valid scenarios and demands of network-triggered on-demand sync signals need to be further identified and discussed.
- Proposal 26 (Sec 3.8): NR RMSI delivery scheme should be inherited to 6GR, with coverage enhancements and NR time domain repetition scheme as starting point.
- Proposal 30 (Sec 3.9): Regarding channel structure for 6GR paging, the legacy NR solution can be considered, i.e., PDCCH + PDSCH.
- Proposal 36 (Sec 4): In 6GR idle mode, at least SSB can be used for DL based RRM measurement for L3 mobility.
- Proposal 38 (Sec 4.1): For beam management in 6GR RRC idle mode, at least 5G NR solution where SSB used for PRACH association serves as QCL source RS without additional beam measurement and reporting can be a baseline.
- Proposal 41 (Sec 4.1): At least transparent M-TRP operation can be considered for initial access; non-transparent M-TRP operation needs justification.
- Proposal 42 (Sec 4.2): Beam prediction for 6GR initial access (Sub-use case D) should be studied, leveraging NR AI-BM experience.
- Proposal 43 (Sec 5): For 6GR cell DTX/DRX operation, enhanced cell DTX/DRX operation compared with NR in RRC connected state and cell DTX/DRX operation in idle state need to be studied.