R1-2601814
discussion
Discussion on aspects of downlink-based CSI acquisition for 6GR
From Spreadtrum
Spreadtrum's prior position on
10.5.3.1
at
RAN1#124
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Proposes a unified CSI acquisition framework design that associates a CSI report configuration with a channel measurement configuration and/or an interference measurement configuration, supporting multiple scenarios including early CSI for candidate cells. Proposes studying both NW-controlled and UE-initiated CSI reporting, and considers PUSCH-only based CSI reporting for all time domain behaviors in 6GR. For CSI-RS design, supports up to 128 ports per single CSI-RS resource and proposes PN sequence with UE-specific seed with component RE pattern aggregation. On AI/ML, presents technical case showing JSCC/JSCM performance gains over SSCC especially at low SNR but proposes postponing two-side model work until NR standardization completes. Prioritizes low overhead CSI-RS for 6GR Day 1 AI use case, presenting evaluation results showing less than 5% SGCS loss with 87% frequency domain and 75% spatial domain RS overhead reduction, while noting spatial domain generalization across deployment scenarios needs further study due to approximately 28% SGCS loss.
Summary
Spreadtrum's R1-2601814 presents 21 proposals and 12 observations on 6G downlink CSI acquisition, covering a unified CSI framework, basic CSI-RS design supporting up to 128 ports, and AI/ML-based CSI compression and low-overhead CSI-RS. The document recommends postponing two-side AI/ML models (JSCC/JSCM) until NR work completes while prioritizing low-overhead CSI-RS as a Day-1 6G AI use case.
Position
Spreadtrum proposes a unified CSI acquisition framework spanning sTRP, mTRP, mTRP calibration, and early CSI scenarios, preferring to study inclusion of candidate cell early CSI rather than creating separate frameworks. They oppose L2-based (MAC-CE) CSI reporting as a Day-1 6G priority, arguing it introduces substantial latency from MAC PDU construction and HARQ retransmission, and incurs significant overhead from MAC sub-headers and CRC compared to L1 UCI. For CSI-RS design, Spreadtrum supports up to 128 ports as a starting point (opposing 256 ports due to UE measurement complexity), requires using a single CSI-RS resource to contain all ports rather than resource aggregation, and proposes sparse frequency/spatial domain density combined with component RE pattern aggregation for overhead reduction. On AI/ML, Spreadtrum presents a case for postponing JSCC/JSCM standardization until NR two-side model work completes, citing unresolved inter-vendor issues, while prioritizing low-overhead CSI-RS reconstruction as the Day-1 6G AI use case based on simulation results showing less than 5% SGCS loss with 87% frequency domain and 75% spatial domain RS overhead reduction.
Key proposals
- Proposal 1 (Sec 2.1.1): Strive to design a unified CSI acquisition framework supporting multiple scenarios. Study whether/how early CSI for candidate cell(s) can be included in unified CSI acquisition framework.
- Proposal 2 (Sec 2.1.1): For CSI acquisition framework, support to associate a CSI report configuration with a channel measurement configuration and/or an interference measurement configuration.
- Proposal 6 (Sec 2.1.2): Consider CSI measurement over aperiodic, periodic and semi-persistent RS.
- Proposal 10 (Sec 2.1.3): For the time domain behavior of CSI reporting, consider at least periodic and aperiodic. Study whether semi-persistent CSI reporting is needed.
- Proposal 12 (Sec 2.1.3): For CSI acquisition, study both implicit CSI feedback (PMI, RI, CQI) and explicit CSI feedback (channel matrix, channel eigen-vector).
- Proposal 13 (Sec 2.1.3): Regarding PMI, strive to design a unified codebook for SU-MIMO and MU-MIMO, and for sTRP and mTRP use cases.
- Proposal 15 (Sec 2.2): Regarding the number of CSI-RS ports, support up to 128 as starting point.
- Proposal 16 (Sec 2.2): For either X<=32-port or X>32-port CSI-RS in 6GR, support using one CSI-RS resource to contain the X ports.
- Proposal 17 (Sec 2.2): For CSI-RS overhead reduction, consider sparse density in frequency and spatial domains.
- Proposal 19 (Sec 2.2): Consider CSI-RS RE pattern as aggregated by one or multiple component RE patterns.
- Proposal 20 (Sec 2.3): Given that the standardization work for the two-side model has not yet been completed, JSCC/JSCM can be postponed until the work in NR is completed.
- Proposal 21 (Sec 2.4): Prioritizing low overhead CSI-RS for 6GR Day 1 AI use case.
- Proposal 5 (Sec 2.1.1): For 6G-R, study early CSI acquisition including UE transition from IDLE/INACTIVE to CONNECTED mode, lower layer mobility, and SCell deactivation/dormancy to activation.
- Proposal 7 (Sec 2.1.2): Study mechanism to support dynamic port on/off switching for channel measurement RS.
- Proposal 11 (Sec 2.1.3): Consider PUSCH-only based CSI reporting for all supported time domain behaviors in 6GR.