R1-2601845
discussion
On the design of WUS with OFDM based sequence
From Nokia
Nokia's prior position on
10.6.1.1
at
RAN1#124
· AI-synthesized, paraphrased
verify sources →
Proposes assuming a more stringent residual CFO of 1 ppm for the EE processing state, arguing that SSB-based calibration during active states can maintain this accuracy from initial cell search. Requires the minimum number of RX chains for 6G WUS reception to depend on RRC state and frequency range, noting that deep/ultra-deep sleep states justify single RX chain operation due to lack of channel state information and CFO accuracy. Proposes exploring m-sequence and Gold sequence families as alternatives to Zadoff-Chu for 6G WUS, while requiring evaluation of sequences based on auto correlation peak prominence, low cross correlation performance, and receiver complexity. Proposes studying both direct subgroup-specific sequence mapping (codepoint scheme) and segmented bitmap mapping to OFDM sequences, noting that controlling the number of segments allows the design to mimic either scheme. Also proposes striving for WUS coverage equivalent to paging PDCCH coverage at aggregation levels 8 and 16.
Summary
Nokia presents 19 observations and 9 proposals for the design of a 6G OFDM-based Wake-Up Signal (WUS) in Release 20, focusing on CFO assumptions, sequence selection, information mapping, and coverage targets to enable energy-efficient UE operation.
Position
Nokia proposes that RAN1 should assume a residual CFO of 2 ppm for the EE processing state rather than the previously agreed 5 ppm, arguing this benefits WUS signal design. They require RAN1 to explore sequence families beyond Zadoff-Chu, specifically m-sequence and Gold sequence, and evaluate them using auto-correlation peak prominence, cross-correlation, and receiver complexity as KPIs. They propose studying both subgroup-specific sequence mapping and segmented bitmap mapping schemes, with the design controlled by the number of segments to mimic either approach. For coverage, they require that WUS match paging PDCCH coverage (AL8 and AL16) in RRC IDLE mode and extend the same target to RRC CONN mode, citing the ability to use more receive chains.
Key proposals
- Proposal 1 (CFO Assumption): RAN1 should assume residual CFO of 2 ppm for EE processing state for efficient use of 6G WUS signal design.
- Proposal 2 (Sequence family): Unlike 5G, where Zadoff-Chu sequence is overlaid on OOK, RAN1 shall explore the possibility of other sequence families, such as m-sequence, Gold sequence, can be considered for 6G WUS.
- Proposal 3 (Sequence family): RAN1 shall evaluate sequences, if any, using the following KPIs, namely, auto correlation peak prominence, low cross correlation performance, and the receiver complexity to generate and correlate multiple sequences.
- Proposal 4 (Sequence length): Depending on the coverage requirements and minimum channel BW, the length of WUS sequence can be extended up to 256.
- Proposal 5 (Information Mapping and Subgroups): RAN1 shall study direct mapping of a specific sequence to a subgroup and a sequence indicating the wake-up of all subgroups.
- Proposal 6 (Information Mapping and Subgroups): RAN1 shall study bitmap scheme with segmented bits mapped to a specific sequence.
- Proposal 7 (MO Design): RAN1 shall design WUS to provide wake-up indication of subgroups by encoding the content using at least 8 different OFDM sequences that UE can monitor in an OFDM symbol.
- Proposal 8 (Coverage and System Overhead): RAN1 shall strive to achieve the WUS coverage same as that of paging PDCCH coverage (AL8 and AL16) at least for RRC IDLE mode.
- Proposal 9 (Coverage and System Overhead): RAN1 shall strive to achieve the WUS coverage target same as the RRC IDLE mode coverage as the UE may use more receive chains and processing power.