R1-2600192
discussion
Discussions on 6GR Uplink Transmission
From OPPO
Summary
This document contains approximately 30 proposals and 7 observations across 6 sections covering 6G uplink PUSCH and PUCCH design, addressing codebook-based transmission, coherent MIMO, DMRS design (including AI/ML-based superimposed pilots), power control, and PUCCH formats.
Position
OPPO requires codebook-based UL transmission as the 6G day 1 baseline and proposes studying non-codebook-based feasibility only after evaluating hardware cost and complexity for antenna calibration. They present technical case for UE-assisted coherent state reporting and multiple RAN4 coherency capability levels, arguing that practical UEs lose lab-verified coherency due to implementation-dependent events such as PA non-linearity, temperature extremes, and antenna blocking. OPPO proposes a unified/fixed uplink codebook framework for 1,2,3,4,[8] ports with at least fully-coherent and non-coherent codebooks, while further studying downloadable or mixed codebooks for different UE antenna models. They require frequency-selective precoding to be limited to configuration with more than 4 ports using CP-OFDM, citing no gain for 2/4-port or large subband sizes, and propose TPMI overhead reduction via less frequent TPMI update based on observed slower PMI variation relative to CQI. OPPO proposes 6G support only a single DMRS type (Type 2-like) with extension in frequency domain for more than 24 orthogonal ports, and introduces study of both low-density DMRS (PRB-level and slot-level) and AI/ML-based SuperImposed Pilot (SIP) schemes that completely eliminate DMRS time-frequency overhead by superimposing pilots and data on the same REs.
Key proposals
- Proposal 1 (Sec 2.1): Consider supporting coherent transmission of practical 6GR UEs, designing uplink codebook for different ports with a whole picture, robust performance for coverage-limited/high mobility cases, supporting full power mode at 6G day 1, and considering low/zero overhead DMRS for different scenarios.
- Proposal 1 (Sec 2.2.1): Codebook based UL transmission can be baseline for 6G day 1.
- Proposal 1 (Sec 2.2.2): Consider UL coherent MIMO with UE-assisted signaling report and multiple requirements to support UEs with different coherent capabilities/levels.
- Proposal 1 (Sec 2.2.3): Support unified/fixed uplink codebook for 1,2,3,4,[8] ports in 6G day 1.
- Proposal 1 (Sec 2.2.4): Consider frequency selective precoding only for larger than 4 ports and CP-OFDM, taking TPMI overhead, channel estimation performance and PAPR into account.
- Proposal 1 (Sec 2.2.5): Consider TPMI overhead reduction for uplink especially for large number of antenna ports or frequency selective precoding.
- Proposal 1 (Sec 2.2.6): Consider UL TxD for coverage-limited and high mobility UEs in 6G.
- Proposal 1 (Sec 2.3.1): Consider design principles for 6G regular UL DMRS: strive to only support single DMRS type, the same design for DL/UL DMRS as much as possible, nested structure for different number of DMRS ports, potentially support more orthogonal DMRS ports, and take the fundamental design of Rel-15/18 DMRS as starting point.
- Proposal 1 (Sec 2.3.2): 6G only supports single DMRS Type, e.g. Type 2 like DMRS.
- Proposal 1 (Sec 2.3.3): Consider simplified port indication signaling to support more DMRS ports.
- Proposal 1 (Sec 2.3.5): For DMRS overhead reduction, study the uplink SuperImposed Pilot (SIP) scheme with DMRS and data over the same resource elements.
- Proposal 1 (Sec 2.4.1): Consider to down select one from power control parameters associated with SRI or power control parameters associated with unified TCI state.
- Proposal 1 (Sec 2.4.3): Support UE to report capability of full power per port (similar to full power mode 0 in NR) in 6G day 1.
- Proposal 1 (Sec 3.1): Sequence-based PUCCH format for small payload UCI should be supported; a NR PF1-like channel structure with configurable time-domain resources, frequency-domain resources and spreading factor can be considered as a baseline.
- Proposal 1 (Sec 3.3): Prefer power control parameters associated with unified TCI state instead of PUCCH-SpatialRelationInfo in 6GR.