R1-2600037
discussion
On transmission schemes for uplink channels in 6GR
From Nokia
Summary
This document from Nokia contains 23 Observations and 31 Proposals addressing uplink transmission schemes for 6GR, covering PUCCH simplification, PUSCH MIMO layer imbalance mitigation, DMRS design for up to 48 antenna ports, enhanced multi-slot resource allocation, and AI/ML receiver evaluation frameworks for sparse and DMRS-free operation.
Position
Nokia proposes simplifying 6GR UCI arbitration by limiting CSI reporting to PUSCH only and adopting slot-level one-shot multiplexing/prioritization to eliminate the iterative symbol-level procedures of NR. They argue NR's five PUCCH formats are excessive and proposes a limited set of scalable PUCCH formats with high similarity to PUSCH design for larger UCI sizes. For PUSCH, Nokia identifies MIMO layer imbalance as a significant performance degradation factor and proposes studying multi-codeword operation and MCS table optimizations to decouple modulation order from code rate, along with new codeword-to-layer mapping to mitigate imbalance. They require a single unified DMRS type with a scalable comb-type pattern supporting up to 48 orthogonal antenna ports, using Rel-18 e-type 1 as baseline, and propose native multi-slot PUSCH resource allocations exceeding 14 symbols rather than NR's slot-bounded framework with later-release optional extensions. For AI/ML receivers, Nokia presents simulation evidence of throughput gains with sparse DMRS and proposes studying three categories of sparse DMRS patterns (time-domain, frequency-domain, and combined) within the unified 6G DMRS framework while emphasizing realistic aligned evaluation assumptions for both AI and legacy receivers.
Key proposals
- Proposal 1 (Sec 2.1): Study CSI reporting via PUSCH only for 6GR, where CSI reporting via L2 and via L1 signaling are considered.
- Proposal 2 (Sec 2.1): Study one-shot UCI multiplexing/prioritization with timeline conditions determined at PUCCH slot level.
- Proposal 3 (Sec 2.2): In 6GR, PUCCH transmission schemes continue to be defined as PUCCH formats.
- Proposal 4 (Sec 2.2): Consider PUCCH formats that are scalable in terms of supported UCI sizes and PUCCH durations.
- Proposal 5 (Sec 2.2): For UCI sizes of tens of bits or larger, high similarity with PUSCH design, e.g. in terms of DMRS symbols, should be considered.
- Proposal 6 (Sec 3.1): Study codeword-to-layer mapping for layer imbalance mitigation in uplink.
- Proposal 7 (Sec 3.1): Study MCS table design in 6G to consider layer imbalance in uplink.
- Proposal 8 (Sec 3.2): Study the need for higher number of PUSCH DMRS antenna ports up to 48 APs.
- Proposal 10 (Sec 3.2): Strive for single DMRS type and single scalable pattern for 6GR considering channel estimation performance and complexity.
- Proposal 13 (Sec 3.2): Study multi-slot based PUSCH DMRS design in 6GR.
- Proposal 17 (Sec 3.3): Study PUSCH resource allocations of more than 14 OFDM symbols in addition to the NR (slot-based) PUSCH (repetitions).
- Proposal 19 (Sec 3.3): 6GR to support only contiguous PUSCH frequency domain resource allocation based on FDRA Type 1.
- Proposal 22 (Sec 3.4): Study new UL power control solutions for: (1) mitigating impacts of energy saving features and interference, (2) adaptive maximum output power, (3) enhanced assistance information and (4) AI/ML based pathloss prediction.
- Proposal 23 (Sec 4.2): RAN1 defines the evaluation assumptions for AI-receivers (e.g. benchmark definition, DMRS configuration, and usedness of free up REs) to compare DMRS patterns (including sparse DMRS) for legacy receivers and AI.
- Proposal 25 (Sec 4.3): For AI receivers, RAN1 to study sparse DMRS configurations for 6G that reduce DMRS overhead while remaining aligned with the unified 6G DMRS framework.