R1-2600194
discussion
Discussion on downlink based CSI acquisition
From OPPO
Summary
OPPO's Tdoc R1-2600194 provides 17 observations and 37 proposals on the 6G CSI framework, recommending the NR CSI framework as the baseline with simplifications. Key proposals include supporting up to 256 CSI-RS ports, studying AI/ML-based CSI-RS overhead reduction, adopting a unified fixed codebook with low/high-resolution types, studying JSCC/JSCM for CSI feedback, and addressing specific scenarios like mTRP and NES.
Position
OPPO proposes using the NR CSI framework as a starting point for 6G, requiring simplification of CSI-ReportConfig and CPU/timeline calculations to avoid over-design. They propose supporting up to 256 CSI-RS ports, asserting that 512 ports provide no additional performance gain, and recommend large CSI-RS periodicity (e.g., 20ms) for realistic evaluation. For codebook design, they propose a unified fixed codebook baseline with low-resolution (Type I scheme A as starting point) and high-resolution (eType II with layer-common or layer-specific SD basis) types, while also studying downloadable codebooks as a complement. They present technical evaluations showing JSCC and JSCM with two-side models alleviate cliff effects in CSI feedback, and they propose studying fusion of downlink CSI feedback with SRS measurements for TDD systems.
Key proposals
- Proposal 2 (Sec 2.2): For CSI evaluation, it is recommended to assume large CSI-RS periodicity (e.g. 20ms) rather than small CSI-RS periodicity (e.g. 5ms) for realistic performance.
- Proposal 3 (Sec 2.2): It is sufficient to support CSI-RS design and CSI report for up to 256 ports.
- Proposal 4 (Sec 3.2.1): Unified design for CSI-RS resources with different number of antenna ports in 6G.
- Proposal 10 (Sec 3.2.3): For CSI-RS overhead reduction, study the channel prediction with sparse CSI-RS in spatial and/or frequency domain.
- Proposal 12 (Sec 4.1): 6GR supports unified and fixed codebook as baseline codebook.
- Proposal 17 (Sec 4.1): For high resolution codebook in 6G, consider the following candidates: eType II CB with layer-common SD basis (L>1); eType II CB with layer-specific SD basis (L>=1).
- Proposal 20 (Sec 4.4.1): To facilitate accurate CSI feedback with limited UL overhead, study the following CSI feedback schemes in 6GR: Joint Source and Channel Coding (JSCC) with two-side model; Joint Source and Channel coding and Modulation (JSCM) with two-side model.
- Proposal 22 (Sec 4.5): For 6GR, support carrying CSI report in L1 signaling.
- Proposal 25 (Sec 5.1): CSI enhancement for NC-JT transmission could be deprioritized in 6GR.
- Proposal 30 (Sec 5.2): Study CSI report for SD and PD NES considering the following aspects: Design following unified CSI framework; CSI overhead reduction considering correlation among different CSIs.
- Proposal 31 (Sec 5.3): Study early CSI report during RRC connection establishment for 6GR.
- Proposal 33 (Sec 5.5): The following two mechanisms for xDCP measurement and report can be studied for 6GR: xDCP report from UE based on DL measurement; SRS based xDCP measurement at gNB.
- Proposal 34 (Sec 5.6): Study fusion of downlink CSI feedback and SRS measurement in 6GR.
- Proposal 36 (Sec 5.8): Consider UE initiated CSI reporting in 6G to avoid unnecessary CSI report.
- Proposal 37 (Sec 5.9): Study CSI report mechanism for multiple carriers within one cell in 6GR.