Semi-Static HARQ-ACK Codebook Payload Reduction via Slot Exclusion
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Solution Overview
Problem
The existing semi-static HARQ-ACK codebook determination in 3GPP 5G New Radio (NR) results in a large HARQ-ACK codebook size, leading to significant overhead, especially with the introduction of the PDSCH-to-HARQ_feedback timing indicator field, necessitating methods for payload reduction while maintaining consistency between the User Equipment (UE) and gNB.
Innovation Solution
The proposed solution involves determining the downlink association set for the semi-static HARQ-ACK codebook by excluding specific slots based on predefined rules, including excluding slots configured only for UL, slots before or after the gNB-initiated COT, and slots with failed PDSCH receptions, and dynamically handling overlapping slots or carriers with failed LBT, thereby reducing the codebook size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the semi-static HARQ-ACK codebook includes all downlink slots in the association set, then the codebook completeness is maintained, but the codebook size becomes large causing significant overhead
Solution Approach 1:
The patent extracts and removes unnecessary slots from the downlink association set based on predefined rules (e.g., excluding slots with failed LBT, slots configured only for UL, slots before/after gNB-initiated COT). This extraction reduces the codebook size while maintaining completeness for valid downlink transmissions, directly resolving the contradiction between codebook size and completeness.
Solution Approach 2:
The patent applies different quality characteristics to different slots within the association set. Not all slots are treated equally - only slots meeting specific criteria (successful LBT, valid downlink configuration, within COT boundaries) are included. This local differentiation allows selective inclusion that reduces overall codebook size while preserving necessary completeness.
2Quantity of substance
If the HARQ-ACK codebook size is reduced by excluding slots, then the overhead is minimized, but the complexity of determining the association set increases
Solution Approach 1:
The patent performs preliminary actions by pre-defining exclusion rules before HARQ-ACK codebook generation. The rules (excluding slots with failed LBT, UL-only slots, slots outside COT) are established in advance, allowing the UE to simply apply these pre-established criteria rather than performing complex real-time determination, thus reducing operational complexity.
Solution Approach 2:
The UE autonomously determines the downlink association set by self-applying the predefined exclusion rules to the received downlink transmission information. This self-service approach eliminates the need for complex gNB-side computation or signaling, reducing system complexity while achieving codebook size reduction.
3Quantity of substance
If slots with failed LBT are excluded from the codebook, then the codebook payload is reduced, but the synchronization between UE and gNB may be affected
Solution Approach 1:
The patent incorporates feedback mechanisms where the UE reports HARQ-ACK information for excluded slots to the gNB. This feedback ensures that even though slots with failed LBT are excluded from the codebook payload, the gNB remains informed and can maintain proper synchronization and retransmission control, resolving the contradiction between payload reduction and synchronization reliability.
Data Source
AI summary
Methods, a remote unit and a base unit are disclosed. According to one embodiment, a remote unit comprising: a receiver that receives, from a base unit, one or multiple downlink transmissions within a channel occupancy time initiated by the base unit; a processor that determines a downlink association set for a HARQ-ACK codebook, excludes one or more downlink slots from the downlink association set based on a predefined rule, and generates the HARQ-ACK codebook corresponding to the downlink association set, wherein the HARQ-ACK codebook comprises HARQ-ACK information bits for the one or multiple downlink transmissions; and a transmitter that transmits the HARQ-ACK codebook to the base unit.