R1-2600058
discussion
Aspects of uplink-based CSI acquisition
From FUTUREWEI
Summary
This Futurewei contribution presents 13 proposals and 3 observations on 6G uplink-based CSI acquisition, advocating for evolving the 5G NR MIMO/RS/CSI framework rather than a fundamental redesign. The document covers MIMO framework design with AI/ML integration, UL-based CSI acquisition for hybrid antenna architectures in upper midband (UMB), UL carrier switching enhancements, SRS enhancements for cooperative MIMO and interference probing, and QCL/TCI framework evolution.
Position
Futurewei proposes that 5G NR MIMO/RS/CSI framework serves as the starting point for 6G with enhancements focused on upper midband (UMB) support, general SE/UPT performance, and fast FR2 beam acquisition. They propose integrating AI/ML as part of the 6G MIMO framework from day-1, urging RAN1 to discuss high-level MIMO framework principles enabling AI/ML-based functionality and identifying AI/ML use cases to facilitate assessment. For UMB base stations, they propose hybrid antenna architecture as a key focus area for panels with >512 elements or ≥100 MHz bandwidth, specifying particular antenna combinations to study (2048 elements with 256 TXRUs at 7 GHz; 2048 elements with 32 or 128 TXRUs at 15 GHz) and proposing enhanced SRS repetition schemes for fast full CSI acquisition to support efficient MU-MIMO. They propose a general carrier switching framework that reduces/eliminates switching-back by moving all transmissions to the switching-to carrier and maintaining one set of signals/channels over n carriers, potentially combined with DL carrier switching. They propose studying cooperative MIMO via DL interference probing based on SRS enhancements, presenting simulation results showing capacity gains of 64.8% in dense urban and 26.9% in urban macro scenarios for 45Mbps XR traffic. They propose QCL/TCI enhancements to enable UL signals such as SRS as QCL source RS for DL TCI states.
Key proposals
- Proposal 1 (Sec 2): For 6G MIMO/RS/CSI, adopt 5G NR MIMO/RS/CSI framework as a starting point and study enhancements for upper midband (UMB) support, general performance (SE and UPT) enhancements, and fast beam acquisition for FR2.
- Proposal 2 (Sec 2): RAN1 to discuss high-level MIMO framework principles that enable integration of AI/ML-based functionality from day-1 of 6G, which also facilitates evaluation for AI/ML use cases.
- Proposal 3 (Sec 2): Identify a few AI/ML use cases to facilitate the study and assessment of AI/ML-ready MIMO framework design.
- Proposal 4 (Sec 4.1): For UMB base stations, hybrid antenna architecture with a large number of antenna elements (>512) and moderate number of TXRUs supporting hybrid beamforming should be a key focus area for carriers with ≥100 MHz bandwidth or frequencies at the high upper midband.
- Proposal 6 (Sec 4.1): For hybrid BS antennas, study the issue of how to acquire full CSI faster for efficient MU MIMO support.
- Proposal 7 (Sec 4.1): Study enhanced SRS transmission (e.g., repetition schemes) for fast full CSI acquisition by hybrid BS antennas.
- Proposal 8 (Sec 4.2): For 6G UL carrier switching, incorporate SRS carrier-based switching into a general carrier switching framework that reduces/eliminates required switching-back and maintains one set of signals/channels over n carriers.
- Proposal 9 (Sec 4.3.1): For 6G SRS, use 5G NR SRS designs as baseline including carrier-based switching, hopping, 1/2/4/8 ports, physical antenna switching, and frequency-domain/time-domain resource allocation.
- Proposal 10 (Sec 4.3.2): Study cooperative MIMO via DL interference probing based on SRS enhancements to improve 6G system capacity for TDD.
- Proposal 11 (Sec 4.3.2): Study cooperative MIMO for TDD with downlink interference probing via SRS including SRS trigger enhancement for dynamic signaling with low overhead, SRS transmission parameters associated with PRB/port allocation of corresponding PDSCH, and SRS beamforming based on DL channel and interference measurement.
- Proposal 12 (Sec 4.4): In 6GR, consider the unified TCI framework developed in 5G NR as a starting point for 6GR QCL/TCI framework.
- Proposal 13 (Sec 4.4): In 6GR, support QCL/TCI enhancements to enable the use of UL signal (e.g., SRS) as QCL source RS of DL TCI states.