R1-2600117
discussion
Discussion on uplink transmission scheme(s) for uplink channels for 6GR
From Spreadtrum
Summary
This Spreadtrum/UNISOC contribution to 3GPP RAN1#124 contains 8 Observations and 26 Proposals addressing 6G uplink channel design. The document provides positions on PUSCH transmission schemes, DMRS design with AI/ML receiver enhancements, and PUCCH simplification, collectively advocating for a streamlined design philosophy that reduces NR complexity while selectively introducing new capabilities.
Position
Spreadtrum 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. They propose 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. For DMRS, they require defining a single DMRS type for both DL and UL to avoid implementation complexity from multi-type support, and they support 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. They oppose prioritizing superimposed pilot (SIP) as a use case pending further multi-user interference evaluation and standardization impact analysis. For PUCCH, they propose radical simplification from five NR formats to two formats (≤2 bits and >2 bits), eliminate 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.
Key proposals
- Proposal 2 (Sec 2.1): 4-port PUSCH transmission scheme in NR can be a starting point to design 6G PUSCH transmission. FFS: 8-port PUSCH transmission scheme can be studied for 6G CPE/FWA.
- Proposal 4 (Sec 2.1): Strive to study a simplified unified uplink codebook to support multiple use cases, e.g. coherent type consumption, full power transmission, transmission from symmetric or asymmetric UL panels etc.
- Proposal 5 (Sec 2.1): Study frequency selective precoding for PUSCH transmission in 6G.
- Proposal 6 (Sec 2.1): Study L1 UE aggregation to improve performance of the uplink transmission in 6G.
- Proposal 7 (Sec 2.1): Study remote shared uplink panel for UL performance enhancement in 6G.
- Proposal 8 (Sec 2.2): For DMRS design, strive to define a single DMRS type for both DL and UL.
- Proposal 12 (Sec 2.2.2): Support DMRS overhead reduction sub-case A for 6GR Day 1 AI/ML use case.
- Proposal 14 (Sec 2.2.2): SIP needs to have sufficient evaluation results before selected as the priority use case. At least the following aspects should be investigated: Interference from multiple users, Standardization impact, e.g., DMRS design.
- Proposal 16 (Sec 3.1): PUCCH should continue to be supported in 6GR, carrying at least SR and HARQ-ACK, but not CSI, while addressing pain points of NR PUCCH.
- Proposal 17 (Sec 3.2): Two PUCCH formats are supported in 6GR: PUCCH format 1 is for UCI with less than or equal to 2 bits, PUCCH format 2 is for UCI with more than 2 bits.
- Proposal 19 (Sec 3.3): Support two types of time-domain behaviors for 6GR PUCCH, only periodic and aperiodic, while semi-persistent PUCCH is not necessary.
- Proposal 24 (Sec 3.3): To optimize PUCCH collision, study the PUCCH resource determination mechanism by prioritizing proactive conflict avoidance mechanism including: PUCCH resource determination in a slot, PUCCH resource determination across slots.
- Proposal 25 (Sec 3.3): Support slot based PUCCH transmission in 6GR, sub-slot based PUCCH and two PUCCH configurations are unnecessary.
- Proposal 26 (Sec 3.4): To design 6G PUCCH transmission scheme(s), consider PUCCH transmission schemes for multi-TRP case in NR as a starting point, study the necessity of other PUCCH transmission schemes.