R1-2600040
discussion
On uplink-based CSI acquisition in 6GR
From Nokia
Summary
Nokia's R1-2600040 presents 30 proposals and 14 observations on uplink-based CSI acquisition for 6G, covering SRS design evolution, UL/DL CSI acquisition, and AI/ML for overhead reduction. The document argues for reusing the 5G NR SRS framework as a baseline while studying enhancements for higher antenna counts, new directional UE antenna models, and dynamic adaptation.
Position
Nokia proposes reusing the existing 5G NR UL SRS design framework, basic resource definition, and Zadoff-Chu sequences as the baseline for 6G, with SRS support up to 8 antenna ports for UEs. For Fixed Wireless Access (FWA) devices, Nokia proposes studying support for more than 8 SRS antenna ports and new antenna-switching configurations. They present system-level simulation results indicating legacy 5G codebooks deliver no notable performance improvement for fully coherent transmissions with the new Rel-19 directional UE antenna model, proposing studies for new codebook designs tailored to handheld devices and potential relaxation of power control to enable non-uniform transmit power allocation across UE antenna ports. Nokia argues that open-loop transmission schemes should remain specification-transparent and proposes studying the use of DMRS or other PUSCH-associated reference signals for UL CSI acquisition to reduce SRS overhead.
Key proposals
- Proposal 1 (Sec 2): Strive for reusing existing 5G UL SRS design framework in 6GR.
- Proposal 12 (Sec 2): Study a need for new antenna-switching configurations and how to support new antenna-switching configurations for FWA devices in 6GR.
- Proposal 18 (Sec 3.1): Study whether/how to improve flexible SRS sounding to facilitate DL channel acquisition for user pairing in DL MU-MIMO operations.
- Proposal 22 (Sec 3.2.1): Study new codebook design for UE handheld devices with a new directional antenna model to address the limitations of the legacy 5G codebooks.
- Proposal 26 (Sec 3.2.2): Further study NCB UL transmission scheme only if UE supports RF reciprocity capability.
- Proposal 28 (Sec 3.2.3): Open-loop transmission schemes should be considered as 'specification transparent' for 6G uplink MIMO.
- Proposal 29 (Sec 3.3): In 6GR, study the use of reference signals other than SRS, associated with PUSCH transmissions, for UL CSI acquisition (inc. for rank and TPMI updates etc.).
- Proposal 30 (Sec 3.4): Study SRS as a potential QCL source reference for 6G UL beam management.
- Proposal 5 (Sec 2): For FWA devices in 6GR, RAN1 should study how to support higher number of SRS APs >8.
- Proposal 7 (Sec 2): Study how antenna port imbalance impacts to CSI obtained via SRS antenna-switching and related procedures.
- Proposal 9 (Sec 2): Study different mechanisms and techniques to enhance UL SRS multiplexing capacity as well as SRS interference randomization in 6GR.
- Proposal 14 (Sec 2): Strive for enhancing support for semi-persistent and aperiodic UL SRS transmission procedures and related signaling for UL/DL CSI in 6GR.
- Proposal 23 (Sec 3.2.1): RAN1 to study potential relaxation of power control requirements for PUSCH and SRS transmissions, enabling non-uniform transmit power allocation across UE antenna ports.
- Proposal 24 (Sec 3.2.1): Study the impact of channel aging on the codebook-based UL MIMO performance for different UE speeds.