R1-2601840
discussion
On uplink-based CSI acquisition in 6GR
From Nokia
Nokia's prior position on
10.5.3.2
at
RAN1#124
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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, proposes studying support for more than 8 SRS antenna ports and new antenna-switching configurations. Presents 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. 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.
Summary
This Nokia contribution (R1-2601840) presents 10 observations and 24 proposals focused on UL-based CSI acquisition for 6GR, emphasizing reuse of the 5G SRS design framework while identifying specific enhancements needed for capacity, coverage, latency, and new device types.
Position
Nokia proposes reusing the existing 5G UL SRS design framework, basic SRS resource definition, and Zadoff-Chu sequences as foundational building blocks for 6GR. They propose studying enhancements to TD-OCC upon SRS repetition for multiplexing capacity and co-scheduling of PUSCH with UL SRS without impacting channel estimation. For FWA devices specifically, they propose studying support for SRS APs greater than 8 and new antenna-switching configurations. They propose studying the use of DMRS associated with PUSCH transmissions as a complementary or alternative CSI acquisition mechanism to SRS, citing discrepancies in power and interference between SRS and PUSCH. They strive for streamlining through unified SRS configurations across aperiodic, semi-persistent, and periodic types, as well as unified frequency hopping.
Key proposals
- Proposal 1 (Sec 2): Strive for reusing existing 5G UL SRS design framework in 6GR.
- Proposal 5 (Sec 2): For FWA devices in 6GR, RAN1 should study how to support higher number of SRS APs >8.
- Proposal 9 (Sec 2): Study different mechanisms and techniques to enhance UL SRS multiplexing capacity, like TD-OCC upon SRS repetition, as well as SRS interference randomization in 6GR.
- Proposal 14 (Sec 2): Study need for new antenna-switching configurations and how to support new antenna-switching configurations for FWA devices in 6GR.
- Proposal 19 (Sec 2): Study SRS transmission procedure to facilitate sounding in the UL of all parts of the DL bandwidth where the DL bandwidth is larger than supported UL CBW so that switching gaps can be minimized by e.g. defining/assuming that the UE changes from one UL CBW to another during DL phase/slots.
- Proposal 20 (Sec 3.1): Study whether/how to improve DL CSI acquisition for TDD systems, especially with large bandwidths.
- Proposal 22 (Sec 3.2): In 6GR, study using UL RS, such as DMRS, associated with PUSCH transmissions/allocations for the purpose of CSI acquisition (e.g., for rank and TPMI updates).
- Proposal 23 (Sec 3.3): Study SRS as a potential QCL source reference for 6G UL beam management.
- Proposal 12 (Sec 2): Strive for unifying UL SRS configurations among aperiodic, semi-persistent, and periodic in 6GR.
- Proposal 13 (Sec 2): Study unified frequency hopping for 6GR.
- Proposal 7 (Sec 2): Study how antenna port imbalance impacts to CSI obtained via SRS antenna-switching and related procedures.