R1-2601868
discussion
Discussion on aspects of downlink-based CSI acquisition
From ZTE
Summary
This ZTE document on 6G-R CSI acquisition presents 16 formal proposals and 12 observations covering a broad evolution from 5G-NR. Key areas include a flexible CSI framework with decoupled measurement/reporting, a unified fixed codebook based on enhanced Rel-16 eType-II, downloadable codebooks, AI-powered CSI compression, and early CSI acquisition for initial access and handover scenarios.
Position
ZTE proposes a decoupled CSI acquisition framework where measurement and report configurations, as well as their triggering, are separated to natively support features like AI/ML-based beam management and spatial-domain CSI-RS overhead reduction, and opposes moving CSI containers to L2 signaling, requiring L1 (UCI) to carry CSI reports due to latency, reliability, and overhead concerns. For CSI compression, ZTE proposes a unified fixed codebook based on the Rel-16 eType-II structure with layer-specific SD basis selection when L ≤ 2 and layer-common SD basis selection when L > 2, supplemented by both Type-I-like and Type-II-like downloadable codebooks to cover broader scenarios like multi-panel UEs and near-field. ZTE presents a technical case against prioritizing JSCC/JSCCM for AI-powered CSI compression, arguing that performance gains diminish to ~2.5% SGCS at typical SINR ranges and requiring further justification on NW-side complexity, reliability, PAPR, generality, and scalability, while supporting SSCC with a UE-sided linear matrix and NW-sided AI model. ZTE proposes early CSI acquisition during initial access and inter-cell-cluster handover to enable mTRP CJT for small/medium-sized data packets that dominate >90% of real-field traffic, with early CSI reports transmittable before or after handover command reception. For CSI-RS, ZTE proposes supporting up to 256 ports in a single resource with cross-RB/slot mapping, and a hybrid high-density + low-density CSI-RS transmission pattern with UE-side AI/non-AI channel prediction to reduce overhead for ultra-massive MIMO.
Key proposals
- Proposal 1 (Sec 3.4): For 6G-R CSI acquisition framework, study at least decoupled measurement & report configurations, decoupled triggering of measurement & reporting, and dynamic update of key parameters for CSI report configurations.
- Proposal 2 (Sec 3.5): For 6G-R CSI acquisition framework, support using L1 signaling (i.e., UCI) to carry the CSI report.
- Proposal 3 (Sec 4.1.2): For 6G-R CSI compression, support a unified fixed codebook with the Rel-16 eType-II codebook structure.
- Proposal 5 (Sec 4.2.2): For 6G-R CSI compression, study both Type-I-like and Type-II-like downloadable codebook.
- Proposal 6 (Sec 4.3.3): For 6G-R CSI compression, study AI-powered CSI compression following the principles that 5G-NR AI/ML-based CSI compression should serve as the baseline and the performance-complexity trade-off should demonstrate improvement over 5G-NR at both UE and NW side.
- Proposal 7 (Sec 4.3.4): For 6G-R CSI compression, AI-powered JSCC/JSCCM should be further justified in at least NW-side complexity and cost, reliability and robustness, PAPR, generality, and scalability.
- Proposal 8 (Sec 4.3.5): For 6G-R CSI compression, study AI-powered SSCC with UE-sided linear matrix and NW-sided AI model for CSI reconstruction.
- Proposal 9 (Sec 5.2): For 6G-R, study DMRS-based CSI acquisition for at least DMRS-based CSI feedback for fast link adaptation, DMRS port/rank selection, CQI adjustment, and DMRS-based RSRP/SINR feedback for assisting NW in performing anti-waterfilling.
- Proposal 10 (Sec 6.4): For 6G-R, study UE-assisted CSI measurement and report, including at least TDCP/FDCP/SDCP, CJT calibration report, and UE-assisted report for CJT interference mitigation.
- Proposal 11 (Sec 7.2): For 6G-R, study early CSI acquisition for initial access in mTRP (cell-cluster) CJT scenario, with FFS on SRS/DMRS-based early CSI acquisition.
- Proposal 12 (Sec 7.3): For 6G-R, study at least early CSI acquisition in inter-cell-cluster handover scenario, where an early CSI report can be transmitted before or after the reception of a handover command.
- Proposal 13 (Sec 8.1.4): For 6G-R CSI-RS design, support up to 256 ports in one single resource, and study at least cross-RB or cross-slot CSI-RS resource mapping, CSI-RS pattern for fast CSI acquisition for hybrid beamforming, and CSI-RS power boosting.
- Proposal 15 (Sec 8.2.3): Support a hybrid framework with high-density + low-density CSI-RS transmission pattern to enable AI-based and non-AI-based CSI prediction.
- Proposal 16 (Sec 8.2.4.2): For 6G-R CSI-RS design, study FD/SD low-density CSI-RS with non-AI/AI channel/CSI prediction, prioritizing UE-side implementation/AI model.