R1-2601812
discussion
Discussion on uplink transmission scheme(s) for uplink channels for 6GR
From Spreadtrum
Spreadtrum's prior position on
10.5.2.3
at
RAN1#124
· AI-synthesized, paraphrased
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Proposes using NR closed-loop transmission (codebook-based and non-codebook-based) as the baseline for 6G PUSCH, but requires limiting 8-port transmission to FFS status for CPE/FWA only due to lack of commercial 8-port devices despite NR spec support. Proposes studying a simplified unified uplink codebook with antenna port group configuration to cover full-coherent/partial-coherent/non-coherent types, full power mode transmission, and asymmetric UL panels simultaneously. Requires defining a single DMRS type for both DL and UL to avoid implementation complexity from multi-type support, and supports DMRS overhead reduction sub-case A (sparse orthogonal DMRS in frequency and/or time domain) as a 6GR Day 1 AI/ML use case backed by simulation results showing AI channel estimation with 2-symbol DMRS achieving similar BLER to non-AI with 3-symbol DMRS. Opposes prioritizing superimposed pilot (SIP) as a use case pending further multi-user interference evaluation and standardization impact analysis. For PUCCH, proposes radical simplification from five NR formats to two formats (≤2 bits and >2 bits), eliminating sub-slot based PUCCH, two PUCCH configurations, semi-persistent PUCCH, and PUCCH SCell, while retaining PUCCH group concept and supporting proactive conflict avoidance for PUCCH resource determination.
Summary
Spreadtrum's contribution to 3GPP RAN1#124b provides 23 proposals and 5 observations on 6G uplink transmission schemes, covering PUSCH antenna ports, DMRS design with AI/ML overhead reduction, resource allocation, PUCCH formats, and new technologies like L1 UE aggregation and remote shared uplink panels.
Position
Spreadtrum proposes limiting 6G Day 1 PUSCH antenna ports to {1,2,4}, with 8-port studied only for CPE/FWA, arguing 8-port UEs have not been commercially used despite NR spec support. They propose a simplified unified uplink codebook supporting coherent type consumption, full power transmission, and symmetric/asymmetric UL panels, and study of frequency selective precoding for PUSCH. For multi-TRP, they require using NR schemes as baseline while avoiding multiple transmission schemes for similar scenarios, and propose studying L1 UE aggregation and remote shared uplink panels for performance enhancement. They propose a single DMRS type for UL supporting up to 32 ports with FDM/TDM/CDM multiplexing, and present simulation results showing AI channel estimation with 2-symbol DMRS achieves similar BLER to non-AI with 3-symbol DMRS, supporting DMRS overhead reduction sub-case A for Day 1 AI/ML. They take a cautious stance on superimposed pilot, requiring sufficient evaluation of multi-user interference and standardization impact before selection as priority use case.
Key proposals
- Proposal 1 (PUSCH): Support UE antenna ports {1,2,4} for PUSCH; 8-port studied only for CPE/FWA.
- Proposal 5 (PUSCH multi-TRP): Use NR multi-TRP PUSCH schemes as starting point; avoid multiple schemes for similar scenarios.
- Proposal 7 (New Technologies): Study remote shared uplink panel for UL performance enhancement in 6G.
- Proposal 8 (DMRS Design): Strive to define a single DMRS type for UL.
- Proposal 12 (AI/ML DMRS): Support DMRS overhead reduction sub-case A for 6GR Day 1 AI/ML use case in time, frequency, or joint domains.
- Proposal 14 (Superimposed Pilot): SIP needs sufficient evaluation before selection as priority use case, investigating multi-user interference and standardization impact.
- Proposal 16 (PTRS): Reuse PT-RS in 5G NR as baseline for 6GR.
- Proposal 17 (Time Domain RA): Support only one PUSCH mapping Type with flexible starting symbol; up to 14 symbols; symbol granularity; allocation can cross slot boundary.
- Proposal 19 (Frequency Domain RA): Support physically contiguous allocation determined by starting RB/number of RBs or starting RBG/number of RBGs.
- Proposal 21 (PUCCH): Support Option 1 with dedicated physical channel (PUCCH) for UCI in Layer 1.
- Proposal 22 (PUCCH Formats): Two PUCCH formats: Format 1 for UCI ≤2 bits, Format 2 for UCI >2 bits.
- Proposal 23 (PUCCH Design): Reuse flexible duration/starting symbol and configurable max RB number for PUCCH format with >2 bits from NR.