R1-2601832
discussion
On synchronization acquisition and beam measurement
From Nokia
Nokia's prior position on
10.5.1.1
at
RAN1#124
· AI-synthesized, paraphrased
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Proposes studying ZC sequence-based designs for PSS to exploit robustness against frequency offset, contrasting with NR's m-sequence approach and noting ZC sequences require fewer frequency hypotheses for reliable correlation peak strength. Proposes studying a single PSS sequence to reduce initial cell selection complexity by a factor equal to the number of frequency hypotheses and synchronization raster points. For SSS, proposes Gold sequences as baseline, while noting these sequences lose their autocorrelation/cross-correlation properties under frequency offset, requiring the UE to have sufficient synchronization for IDLE mode measurements. Proposes studying on-demand SIB1 delivery in both stand-alone and non-stand-alone scenarios, extending beyond Rel-19's multi-cell limitation. For FR2-1, requires 240kHz SCS SS/PBCH support to halve the time-domain footprint and increase cell spectral efficiency, with numerical analysis showing 2-12% DL resource gain depending on channel bandwidth and FDM assumptions. Proposes studying AI/ML in initial access by fully reusing Rel-19 AIML beam management models for spatial-domain and temporal-domain DL Tx beam prediction.
Summary
This Nokia 3GPP RAN1 contribution (R1-2601832) on 6G initial access, synchronization, and broadcast signaling presents 38 proposals and 55 observations. It covers sync raster design, SS/PBCH structure with a focus on UE complexity reduction via single PSS sequences, on-demand SIB1/paging delivery for network energy saving, additional on-demand synchronization signals, mobility measurements based on SSS, and AI/ML beam prediction for initial access.
Position
Nokia proposes reducing UE initial cell selection complexity by limiting PSS sequences to one (studying m-sequence and Zadoff-Chu based designs) and by using PSS bandwidth instead of SSB bandwidth for sync raster definition (Option 4) to make the raster sparser without impacting PBCH/SSB performance or channel allocation flexibility. They present evaluation results showing Zadoff-Chu with u=1/2 achieves lowest complexity, while 1/3rd m-sequence with 5 hypotheses and Zadoff-Chu with u=1 have similar complexity. For network energy saving, they propose studying relaxed SS/PBCH periodicity up to 160ms in clustered transmission patterns, on-demand SIB1 delivery extended from Rel-19 to standalone scenarios, and paging-conditional additional synchronization signals. For mobility measurements, they propose SSS-based measurements across all RRC states to ensure consistent cell coverage, with NZP-CSI-RS studied for CONNECTED mode, and argue L3 CSI-RS are not used in practice in NR.
Key proposals
- Proposal 1 (Sec 2): To limit the possible impact of NTN cell search to TN UE initial cell selection, separate synchronisation raster locations should be considered.
- Proposal 4 (Sec 3.2.1): RAN1 should study the benefit of single PSS sequence to reduce the initial cell selection complexity.
- Proposal 5 (Sec 3.2.1.2): RAN1 to consider Gold sequence as a baseline for SSS sequence design.
- Proposal 9 (Sec 3.3): Study the information carried by MIB/PBCH considering the support of energy efficiency and coverage extension related features, i.e. on-demand SIB1 transmission, clustering based cell-common channel and fixed transmissions.
- Proposal 11 (Sec 3.3): 6GR PBCH design should enable PBCH combining by avoiding time variant payload.
- Proposal 14 (Sec 3.4): Evaluate the initial synchronization signals and channel periodicity accounting possible presence of signal/channel repetitions at the start of the cycle in clustered manner in terms of the following KPIs: NES gain, measurement performance (including impact to mobility) and detection performance.
- Proposal 17 (Sec 3.5.1): For frequency ranges using 120kHz SCS (i.e. FR2-1, and potentially the upper part of the around 15GHz range), 240kHz SCS SS/PBCH should be supported for 6GR to enable smaller time domain footprint of SS/PBCH transmissions providing higher cell spectral efficiency.
- Proposal 18 (Sec 4): Consider extending the Rel-19 OD-SIB1 for different deployment scenarios, including the single cell scenario, to realize the additional NES gains.
- Proposal 23 (Sec 5): Study additional on-demand reference signals for facilitating UE synchronization for paging reception.
- Proposal 25 (Sec 6): Study synchronization signal (SS), as measurement signal for mobility in all RRC states.
- Proposal 27 (Sec 6): Study NZP-CSI-RS as mobility measurement signal at least in CONNECTED MODE.
- Proposal 32 (Sec 6.1): Study Radio Link Monitoring for 6GR.
- Proposal 33 (Sec 6.2): Support studying early beam reporting and refinement for 6GR initial access after sufficient progress has been made on the general beam management framework.
- Proposal 36 (Sec 7): Study beam prediction in initial access and RA procedure including the relevant aspects for applying predicted/narrow beams, including predicted beam reporting/refinement during RACH, Msg2/Msg3/Msg4 improvements, and beam management after Msg4.