R1-2600043
discussion
Views on HARQ related aspects in 6GR
From Nokia
Summary
Nokia's contribution on 6G (6GR) HARQ aspects proposes retaining NR's asynchronous adaptive HARQ for UL/DL, and introduces 6 study proposals and 7 observations focused on decoupling UL/DL scheduling coordination for CA and improving missed DL assignment handling via PDCCH detection feedback, totaling 13 proposals/observations.
Position
Nokia proposes that 6GR shall retain NR's asynchronous adaptive HARQ operation for UL-SCH and DL-SCH. They present a technical case against NR's tight coordination between UL and DL schedulers in HARQ-ACK reporting, observing that DAI dependencies in Type-2 HARQ-ACK codebooks and timing indication in DL assignments increase scheduling complexity, and propose studying mechanisms that decouple DL assignment from HARQ-ACK feedback triggering to enable parallel CA processing. They argue that a 6G flexible CA framework with decoupled UL and DL carriers requires HARQ-ACK reporting with decoupled scheduling, targeting a design that allows decoupling of DL scheduling information between cell groups. They also propose studying enhanced feedback techniques including multi-value NACK to differentiate PDSCH decoding failure from missed DL assignment, and indication of detected PDCCH count, to limit the impact of missed DL assignments on adaptive DL HARQ operation.
Key proposals
- Proposal 1 (Sec Esssentials): UL-SCH and DL-SCH operations for 6GR are based on asynchronous adaptive HARQ operation.
- Proposal 2 (Sec Suggested 6G studies): Studies on 6GR HARQ feedback design should consider key requirements including efficient/reliable DL HARQ, simple structure with complex configurations, parallel CA processing without low-latency inter-carrier dependencies, and reduced UL/DL scheduling coordination.
- Proposal 3 (Sec Suggested 6G studies): Study HARQ enhancements to reduce coordination between UL and DL schedulers for single and multiple cells, including decoupling DL assignment from HARQ-ACK feedback triggering and transmission on PUSCH or PUCCH.
- Proposal 4 (Sec Suggested 6G studies): Study Type-3 and Type-2 HARQ-ACK codebooks and enhancements necessary to support HARQ-ACK reporting with decoupled scheduling.
- Proposal 5 (Sec Suggested 6G studies): Target for a 6G HARQ-ACK feedback design that allows decoupling of DL scheduling information between cells or cell groups.
- Proposal 6 (Sec Missed DL assignment): Study feedback techniques with reasonable overhead for PDCCH detection as part of the 6GR PDSCH HARQ feedback framework, including NACK with multiple values and indication of detected PDCCHs or failed PDSCH decodings.
- Observation 1 (Sec Suggested 6G studies): For NR HARQ operation, the UL scheduler for the serving cell receiving HARQ-ACK feedback needs to coordinate with DL schedulers for all DL serving cells transmitting PDSCHs.
- Observation 2 (Sec Suggested 6G studies): For NR Type-2 HARQ-ACK with self-scheduling, DAI information on a DCI scheduling PDSCH depends on simultaneous scheduling decisions on other DL cells, increasing inter-cell scheduling coordination.
- Observation 3 (Sec Suggested 6G studies): For NR Type-2 HARQ-ACK mapped on PUSCH, final DAI information in the UL grant DCI increases scheduling/timing coordination between DL and UL.
- Observation 4 (Sec Suggested 6G studies): HARQ-ACK reporting with decoupled UL and DL scheduling simplifies implementation and allows more parallel processing of different CA serving cells.
- Observation 5 (Sec Suggested 6G studies): For a 6G flexible CA framework with decoupled UL/DL carriers, HARQ-ACK reporting with decoupled UL and DL scheduling is needed.
- Observation 6 (Sec Missed DL assignment): Missed DL assignments severely impact fully adaptive HARQ-ACK operation as the gNB may not use PDSCH re-transmission with reserved MCS or non-self-decodable RV.
- Observation 7 (Sec Missed DL assignment): PDCCH detection feedback can help improve DL control reliability and efficiency, and limit the impact of missed DL assignments on adaptive DL HARQ operation.