HARQ Codebook Determination for Low-Latency Sub-Slot Feedback
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Solution Overview
Problem
The current NR standard does not enable differentiation between PUCCHs in fractional slots, preventing efficient HARQ feedback for multiple PDSCHs within a slot, leading to latency issues in low latency communication services.
Innovation Solution
The method involves dividing downlink and uplink channel slots into sub-slots, with HARQ codebooks constructed for each group of sub-slots, using DCI to determine PUCCH resources based on the latest DCI for each sub-slot, enabling efficient HARQ ACK/NACK feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If semi-static HARQ codebook is used, then feedback structure is simple and fixed, but latency increases due to reserved bits regardless of transmission presence
Solution Approach 1:
The patent implements dynamic HARQ codebook construction where the codebook size and content adapt based on actual transmission conditions. The UE determines which PDSCHs require feedback by checking the dynamic grant DCI, and the codebook is constructed dynamically to include only necessary ACK/NACK bits rather than using a fixed semi-static structure with reserved bits.
Solution Approach 2:
The patent changes the parameter of codebook size dynamically based on the number of actual PDSCH transmissions. The DAI (Downlink Assignment Indicator) field in DCI dynamically indicates the codebook size, allowing the system to adjust the feedback structure parameters to match actual traffic conditions, thereby reducing latency when fewer transmissions occur.
2Loss of time
If dynamic HARQ codebook is used, then latency is reduced by avoiding reserved bits, but device complexity increases due to dynamic determination requirements
Solution Approach 1:
The patent uses the DAI (Downlink Assignment Indicator) field in DCI as a feedback mechanism to inform the UE about the codebook size and which PDSCHs require acknowledgment. This feedback from the gNB simplifies the UE's determination process by providing explicit guidance rather than requiring complex autonomous decisions, thus reducing device complexity while maintaining dynamic latency optimization.
Solution Approach 2:
The DAI field acts as an intermediary that carries information from the gNB to the UE about the HARQ codebook structure. Instead of the UE directly determining complex codebook parameters, the DAI intermediary provides the necessary information, simplifying the UE's task and reducing device complexity while enabling dynamic codebook construction.
3Adaptability or versatility
If multiple PUCCHs are supported within a slot for low latency, then resource allocation flexibility improves, but differentiation between PUCCHs in fractional slots becomes complex
Solution Approach 1:
The patent segments the slot into multiple PUCCH occasions and uses the DAI field to differentiate between them. Each PUCCH occasion is identified by a specific DAI value, allowing the system to support multiple PUCCHs within a slot for low latency feedback while managing differentiation complexity through structured segmentation and explicit identification.
Data Source
AI summary
According to certain embodiments, a method performed by a wireless device includes receiving, from a network node, downlink control information (DCI). The method also includes determining, based on the DCI, a first group of downlink channel sub-slots for downlink channel transmissions. The first group of downlink channel sub-slots corresponds to a group of uplink channel sub-slots and is associated with one or more uplink resources in the corresponding group of uplink channel sub-slots. The method additionally includes constructing a first HARQ codebook comprising acknowledgment (ACK) and/or negative acknowledgement (NACK) feedback for the downlink channel transmissions scheduled in the first group of downlink channel sub-slots. The method further includes transmitting the ACK and/or NACK feedback, using the one or more uplink resources, according to the first HARQ codebook.