R1-2600039
discussion
On downlink-based CSI acquisition in 6GR
From Nokia
Summary
This Nokia Tdoc (R1-2600039) presents 34 proposals and 23 observations on DL-based CSI acquisition for 6GR. It covers CSI-RS design for large arrays (>128 ports), energy savings, AI/ML-based CSI compression and prediction, unified codebook design, and reporting mechanism simplifications, all aimed at enhancing 6GR over the 5G NR baseline.
Position
Nokia proposes establishing 5G Rel-20 CSI-RS design up to 128 APs as the baseline for 6GR CSI acquisition and strives for reusing existing 5G CSI-RS design principles for new 6GR antenna array configurations, including studying new frequency domain densities of 1/16 and 1/32. The company presents a technical case for a unified codebook design that delivers accurate PMI representation across the full range of feedback overhead for both SU-MIMO and MU-MIMO operations, while studying codebook adaptation aspects for different sub-array patterns. Nokia questions the necessity of periodic CSI reporting given semi-persistent reporting flexibility, proposes studying the feasibility of PUSCH-only CSI reporting to simplify UCI handling, and advocates for studying UE-initiated/event-based CSI reporting as a new type. In the AI/ML domain, Nokia observes that JSCC/JSCM primarily improves low-SNR performance by mitigating the cliff effect and that one-sided JSCM performs close to two-sided, while proposing to study generalization, scalability, and fine-tuning for CSI prediction under Rel-18-defined cases.
Key proposals
- Proposal 1 (Sec Overview): 6GR discussions on CSI acquisition framework to consider at least the following guiding design principles: Minimize overhead and save energy while at least maintaining, and preferably increasing, the system performance relative to 5G NR; Tackle CSI aging; Support UEs with different capabilities; Enable flexible CSI reporting; Enable early triggering/activation.
- Proposal 4 (Sec CSI-RS design and transmission): 5G Rel-20 CSI-RS design up to 128 APs should be used as a baseline for 6GR CSI-RS design for CSI acquisition.
- Proposal 7 (Sec CSI-RS design and transmission): Study new frequency domain antenna port densities, e.g. 1/16 and 1/32, for 6GR CSI-RS design and how reduced frequency domain antenna port densities impact PMI selection.
- Proposal 10 (Sec 4.1): 6GR CSI acquisition framework to accommodate coexistence of UEs with different capabilities (e.g., in terms of maximum number of CSI-RS ports, or support of interpolation/prediction), including provisioning flexibility in selecting port group(s) for each UE.
- Proposal 14 (Sec 4.2): Study how to evolve the Rel-18/Rel-19 CSI framework for energy saving in 6GR to at least address the shortcomings of legacy framework, such as by focusing on the following aspects: reducing reporting and higher-layer configuration overhead, considering RS (such as CSI-RS) adaptation, targeting jointly network and UE energy/power savings, studying leveraging SRS for the purpose of spatial adaptation.
- Proposal 17 (Sec 4.4): Study early CSI acquisition mechanisms in 6G to minimize throughput reduction during various UE transition scenarios.
- Proposal 19 (Sec 4.5): In 6GR, study a unified codebook design for PMI compression to target the best trade-off between UPT and overhead for a wide range of feedback overheads, for both SU-MIMO and MU-MIMO operations.
- Proposal 21 (Sec 4.6): Study generalization and scalability for JSCC/M with a baseline of the three cases defined in Rel-18.
- Proposal 23 (Sec 4.7): Study how/whether other DL RSs (e.g., DMRS) than CSI-RS can be leveraged for channel/interference measurements, including which CSI quantities can be derived, to mainly increase CSI accuracy and reduce CSI-RS overhead.
- Proposal 24 (Sec 4.8): In 6GR, study CSI reporting adaptation based on channel correlation metrics, calculated by the UE, in time, spatial, frequency domains, by comparing the following approaches: 1) UE-centric or event-triggered CSI reporting adaptation. 2) UE reporting of channel properties, followed by gNB triggering of CSI reporting based on the UE assistance information.
- Proposal 26 (Sec 4.9): For the frequency and/or spatial domain CSI prediction, study generalization and scalability with a baseline of the three cases defined in Rel-18.
- Proposal 30 (Sec 4.10): Study the benefits of supporting fine-tuning for inference-based CSI prediction in time domain as part of LCM procedures.
- Proposal 31 (Sec 4.11.1): Study the possibility/feasibility to limit CSI reporting to PUSCH-only in 6GR, where CSI reporting via L2 and via L1 signaling are considered.
- Proposal 33 (Sec 4.11.3): Study how CSI triggering and reporting framework can be evolved to avoid unnecessary limitations on PUSCH and PDSCH scheduling.
- Proposal 36 (Sec 4.11.5): Study how/whether to evolve and simplify the CSI processing framework in 6GR.