HARQ-ACK Sub-codebook Combination for 5G NR Feedback
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Solution Overview
Problem
The existing 3GPP 5G NR technology lacks details on determining HARQ enhancement for NR-U with the concept of PDSCH grouping, leading to potential errors in HARQ-ACK codebook construction and subsequent DL performance degradation.
Innovation Solution
A method and apparatus for hybrid automatic repeat request acknowledgement (HARQ-ACK) sub-codebook combination, where a UE receives a DCI format indicating that HARQ-ACK feedback for two PDSCH groups should be transmitted in the same HARQ-ACK codebook, and transmits a codebook with at least two parts, one for each PDSCH group, to prevent errors caused by missing DCI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If HARQ-ACK feedback for multiple PDSCH groups is transmitted in the same HARQ-ACK codebook, then the feedback efficiency is improved, but the risk of misunderstandings between UE and BS due to missing DCI increases
Solution Approach 1:
The HARQ-ACK codebook is segmented into multiple parts, with each part corresponding to a specific PDSCH group. This segmentation allows the UE and BS to clearly identify which PDSCH group each HARQ-ACK bit refers to, preventing misunderstandings even when feedback for multiple groups is transmitted in the same codebook. The segmentation resolves the contradiction by maintaining reliability through clear identification while achieving improved feedback efficiency through combined transmission.
Solution Approach 2:
An indicator field in the DCI format acts as an intermediary to explicitly indicate which PDSCH group the HARQ-ACK feedback corresponds to. This intermediary mechanism allows the UE and BS to unambiguously associate HARQ-ACK bits with specific PDSCH groups, eliminating misunderstandings while enabling efficient combined feedback transmission for multiple groups.
2Quantity of substance
If HARQ-ACK feedback for PDSCH group 0 and PDSCH group 1 are combined in one codebook, then the transmission overhead is reduced, but the complexity of determining the correct codebook structure increases
Solution Approach 1:
The DCI format includes pre-configured indicator fields that specify which PDSCH groups should be feedback in the current HARQ-ACK codebook. This preliminary indication simplifies the codebook construction process by providing clear guidance on the expected codebook structure, reducing the complexity of determination while enabling efficient combined feedback transmission.
Solution Approach 2:
Indicator fields in the DCI format serve as intermediaries that convey the intended codebook structure from the BS to the UE. These indicators simplify the codebook construction process by providing explicit instructions on which PDSCH groups are being acknowledged, reducing determination complexity while maintaining low transmission overhead through combined feedback.
3Ease of operation
If the UE transmits HARQ-ACK feedback assuming a specific last PDSCH reception, then the feedback generation is simplified, but errors occur when the actual last PDSCH differs from the assumed one
Solution Approach 1:
Indicator fields in the DCI format act as intermediaries that explicitly identify the last PDSCH transmission for each PDSCH group. This eliminates the need for the UE to independently determine which PDSCH is the last one, simplifying feedback generation while ensuring accuracy by using the BS's authoritative identification.
Solution Approach 2:
The DCI format includes feedback indicators that inform the UE about the last PDSCH reception status. This feedback mechanism ensures that the UE generates HARQ-ACK feedback based on accurate information provided by the BS, maintaining both simplicity in generation and accuracy in the resulting feedback.
Data Source
AI summary
Embodiments of the present application are related to a method and apparatus for hybrid automatic repeat request acknowledgement (HARQ-ACK) sub-codebook combination under 3GPP (3rd Generation Partnership Project) 5G new radio (NR). A method for wireless communications performed by a user equipment (UE) includes: receiving a downlink control information (DCI) format for scheduling a physical downlink shared channel (PDSCH) transmission in a PDSCH group, wherein the DCI format includes an indicator for requesting that hybrid automatic repeat request acknowledgement (HARQ-ACK) feedback corresponding to the PDSCH group and HARQ-ACK feedback corresponding to another PDSCH group are to be transmitted in same HARQ-ACK codebook, and the PDSCH transmission is a last PDSCH transmission in the PDSCH group received by the UE before transmission of the HARQ-ACK feedback corresponding to the PDSCH group; and transmitting a HARQ-ACK codebook, wherein the HARQ-ACK codebook includes at least two parts, one part comprises HARQ-ACK information bits for the PDSCH group, and the other pad comprises HARQ-ACK information bits for the above mentioned another PDSCH group.