R1-2600122
discussion
Discussion on downlink control channel, scheduling for DL and UL transmission for 6GR
From Spreadtrum
Summary
This document from Spreadtrum/UNISOC provides a comprehensive analysis of NR DCI design issues and presents 30 proposals/observations for 6G DCI formats. It identifies key problems like excessive unicast DCI format pairs, missing BWP switching recovery, cumbersome field re-interpretation for control without data, and underused group common DCIs, then proposes a simplified DCI framework centered on unified fallback, scalable non-fallback, and two-stage DCI structures.
Position
Spreadtrum proposes reducing the number of fallback DCI formats to exactly one DL and one UL format with identical size, and requires fields and bit lengths in DCI scrambled by specific RNTIs to be fixed and independent of RRC configurations. They present a technical case against NR's use of four DL/UL unicast DCI format pairs, citing extreme PDCCH blind decoding complexity and cumbersome size alignment procedures. For non-fallback DCI, they propose studying two-stage DCI structures where only first-stage DCI undergoes blind detection and second-stage DCI carries variable payload without blind decoding, specifically to support multi-carrier scheduling and mixed services with better spectrum utilization. They propose identifying and clarifying which functions necessitate group common DCI rather than unicast DCI, and narrow the scope to only TPC-related commands and energy efficiency functions like NES or UE power saving.
Key proposals
- Observation 1 (Sec 2.1): Fallback DCI formats and non-fallback DCI formats are defined in NR, the former is for basic scheduling and the latter is for advanced scheduling.
- Proposal 5 (Sec 3): Considering the lessons learned from fallback DCI formats in NR and new requirements of 6GR, following points should be taken into account for the fallback DCI design in 6GR:
- Proposal 9 (Sec 4.1): Considering the lessons learned from non-fallback DCI formats in NR and new requirements of 6GR, the following points should be taken into account for the non-fallback DCI design in 6GR:
- Observation 6 (Sec 4.2): Two stage DCI at least has the following advantages: Improved PDCCH reliability, Reduced Constraints of DCI Size Budget, Scalable and forward compatibility design, Better spectrum utilization and flexibility.
- Proposal 12 (Sec 4.2): Study two-stage DCI to support scalable design of non-fallback DCI formats, including only blind detection on the first-stage DCI, and no blind detection for second-stage DCI
- Observation 11 (Sec 5): The highest priority in the study of group common DCI should be to identify and clarify which functions necessitate the use of group common DCI instead of unicast DCI.
- Proposal 13 (Sec 5): Two major functions of group common DCI are identified for 6GR: Function 1: TPC related, e.g. power Control for PUSCH, PUCCH, and SRS; Function 2: energy efficiency related, e.g. NES or UE power saving.
- Proposal 2 (Sec 3): Only one DL and one UL fallback DCI format should be defined, and both should have the same DCI size.
- Proposal 6 (Sec 3): A unified fallback DCI format should be shared across all device types.
- Proposal 11 (Sec 4.1): Strive for unified non-fallback DCI formats for diverse and mixed services.
- Observation 3 (Sec 2.1): When BWP switching DCI is missing, there would be misalignment of active BWP between UE and gNB. Only implementation basis method can recover from missing BWP switching DCI which introduces significant latency.
- Proposal 4 (Sec 3): Fields and their bit lengths in DCI scrambled by a specific RNTI should be fixed and as independent from RRC configurations as much as possible.
- Proposal 10 (Sec 4.1): Scalable and forward compatible design of non-fallback DCI formats.
- Proposal 8 (Sec 3): Fallback DCI formats should be leveraged for new features in the initial access procedure, such as multi-carrier scheduling.
- Observation 2 (Sec 2.1): Four pairs of DL/UL unicast DCI formats are defined in NR, which significantly increase complexity of PDCCH monitoring and blind decoding, especially introduce extremely cumbersome DCI size alignment procedure.