R1-2601789
discussion
Uplink transmission scheme(s) for uplink channels
From FUTUREWEI
FUTUREWEI's prior position on
10.5.2.3
at
RAN1#124
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Proposes adopting the 5G NR MIMO/RS/CSI framework as a 6G baseline without fundamental paradigm shifts, while studying targeted enhancements for upper midband (UMB) support including larger Tx/Rx antenna elements with hybrid architectures. For UL transmissions, proposes studying fine-granularity frequency-selective precoding via per-subcarrier matched-filter that simultaneously achieves finest precoding granularity and wideband channel estimation, presenting a technical case that 5G NR schemes cannot improve both at the same time. Requires studying AI/ML as an integral part of the MIMO framework from day-1, identifying specific use cases to facilitate AI/ML-ready framework design evaluation including AI/ML-based DMRS optimization. Proposes extending the unified TCI framework to support UL signals (SRS) as QCL source RS for DL TCI states, and consolidating UL power control and timing advance mechanisms through flexible component associations via only the unified TCI framework. Proposes studying UL carrier switching that maintains transmission continuity by moving all transmissions to the switching-to carrier and eliminating switching-back operations.
Summary
Futurewei's Tdoc R1-2601789 presents eight proposals and one observation for 6G uplink transmission schemes, covering AI/ML-based DMRS optimization, frequency-selective precoding, QCL/TCI enhancements, and unified frameworks for power control, timing advance, and carrier switching.
Position
Futurewei proposes including AI/ML-based DMRS configuration optimization for UL DMRS enhancement, citing experimental NMSE improvements using lower-density DMRS configurations with LS-based preliminary estimation as input to AI/ML models across SNR ranges of 10-30dB. They propose studying per-subcarrier matched-filter based frequency-selective precoding for UL PUSCH that achieves finest precoding granularity while enabling a single wideband channel estimation, claiming the effective channel impulse response collapses to one dominant zero-lag tap. They require supporting SRS as QCL source RS for DL TCI states to enable fast beam acquisition with mixed antenna architectures. They propose reusing and simplifying the 5G NR UL power control framework by consolidating four components (UL transmission, reference transmission, open-loop PC parameters, closed-loop TPC parameters) within a unified TCI framework. They propose eliminating switching-back overhead in UL carrier switching by moving all ongoing transmissions to the target carrier and maintaining a single set of signal/channel configurations across n carriers.
Key proposals
- Proposal 1 (Sec 2.1.2): Consider including AI/ML-based DMRS configuration optimization as a candidate approach for UL DMRS enhancement in 6G study.
- Proposal 2 (Sec 2.2.3): To support wider bandwidth PUSCH transmission, study fine-granularity frequency-selective precoding in UL transmissions without the need of separate/multiple receive-side channel estimations.
- Proposal 3 (Sec 2.2.3): To support wider bandwidth PUSCH transmission with reduced DMRS overhead in the frequency domain, study reduced DMRS frequency domain densities than 5G NR without reduced channel estimation performance.
- Proposal 4 (Sec 2.3): In 6GR, consider the unified TCI framework developed in 5G NR as a starting point for 6GR QCL/TCI framework.
- Proposal 5 (Sec 2.3): In 6GR, support QCL/TCI enhancements to enable the use of UL signal (e.g., SRS) as QCL source RS of DL TCI states.
- Proposal 6 (Sec 2.4): To provide efficient support of M-TRP, multi-carrier, and multi-beam scenarios in 6G, study to reuse and simplify 5G NR UL power control framework through providing flexible associations among the following four components via a unified TCI framework: Component A: UL transmission of a RS/channel; Component B: A reference transmission configured/indicated according to a unified TCI framework; Component C: Open-loop PC parameters; Component D: Closed-loop TPC parameters.
- Proposal 7 (Sec 2.5): To provide efficient support of M-TRP, multi-carrier, and multi-beam scenarios in 6G, study to support UL timing advance indication via a unified TCI framework.
- Proposal 8 (Sec 2.6): To support wider bandwidth / multi-carriers, study efficient UL switching to incorporate SRS carrier-based switching, PUCCH/PUSCH carrier-based switching, and 6GR UL switching among parts of bandwidth: Reduce / eliminate required switching-back; To maintain transmission continuity, move all transmissions to the switching-to carrier / part of bandwidth; Maintain one set (or m sets, where m << n) of signals / channels over n carriers / parts of bandwidth; May be additionally combined with DL carrier switching.
- Observation 1 (Sec 2.2.1): 5G NR precoding schemes cannot improve both precoding performance via finer precoding granularity in frequency domain and channel estimation performance at the same time.