Type-2 HARQ-ACK Codebook Grouping for 5G NR Unlicensed Spectrum
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Solution Overview
Problem
The challenge in 5G NR systems is efficiently scheduling and timing Hybrid Automatic Repeat Request (HARQ) acknowledgments (ACK) in unlicensed spectrum, particularly due to the listen-before-talk (LBT) requirements, which affect the reliability and timing of HARQ feedback mechanisms.
Innovation Solution
The implementation of Type-2 HARQ-ACK codebook grouping and retransmission procedures, where the user equipment (UE) decodes downlink control information (DCI) to schedule PDSCH groups and multiplex HARQ-ACK bits for transmission in a PUCCH occasion, while refraining from unscheduled PDSCH receptions, and uses set indices and DAIs to manage HARQ-ACK retransmissions effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional HARQ-ACK scheduling is used in NR-U, then HARQ feedback mechanism operates with fixed timing, but LBT requirements cause transmission failures and timing mismatches
Solution Approach 1:
The patent implements dynamic HARQ-ACK scheduling where the UE and gNB can adaptively adjust timing parameters based on LBT outcomes. The gNB receives indication information from the UE about LBT status and dynamically modifies HARQ-ACK transmission timing accordingly, transforming the fixed scheduling mechanism into a flexible one that responds to channel conditions.
Solution Approach 2:
The patent introduces a feedback mechanism where the UE provides indication information to the gNB about LBT status and HARQ-ACK transmission status. This feedback loop enables the gNB to adjust scheduling decisions based on actual transmission conditions, improving reliability while managing complexity through informed control.
2Loss of information
If UE transmits HARQ-ACK for all scheduled PDSCHs, then complete feedback is provided, but LBT failures cause transmission interruptions
Solution Approach 1:
The patent segments the HARQ-ACK feedback into multiple transmission opportunities. Instead of requiring a single transmission containing all HARQ-ACK bits, the system allows split transmissions where the UE can send feedback in multiple smaller packets, each subject to independent LBT attempts, thereby increasing the probability of successful delivery.
Solution Approach 2:
The patent implements preliminary actions by having the UE prepare and buffer HARQ-ACK information in advance, along with indication information about LBT status. This preparation allows the UE to quickly transmit feedback when channel conditions permit, reducing the impact of LBT failures and maintaining feedback completeness.
3Device complexity
If fixed HARQ-ACK timing is enforced, then scheduling simplicity is maintained, but LBT requirements create timing conflicts and transmission failures
Solution Approach 1:
The patent transforms fixed timing into dynamic timing by allowing the gNB to adjust HARQ-ACK transmission timing based on LBT status indications received from the UE. The system maintains relative timing structure for simplicity while introducing flexibility where needed, balancing complexity and reliability.
4Loss of information
If UE includes HARQ-ACK bits for unscheduled PDSCH receptions, then complete feedback coverage is achieved, but transmission resources are wasted
Solution Approach 1:
The patent applies partial action by having the UE selectively include HARQ-ACK bits only for scheduled PDSCH receptions in the feedback transmission. The UE uses indication information to determine which PDSCHs were actually scheduled and transmitted, excluding unscheduled PDSCHs from the feedback, thereby avoiding waste of transmission resources on non-applicable data.
Data Source
AI summary
A user equipment (UE) configured for operation in a fifth-generation new radio (5G NR) system may be configured for Type-2 Hybrid automatic repeat request (HARQ) acknowledge (ACK) (HARQ-ACK) codebook grouping and HARQ-ACK retransmission. The UE may decode a downlink control information (DCI) format for scheduling a physical downlink shared channel (PDSCH) group of one or more PDSCHs. The DCI format may include a downlink assignment index (DAI) comprising a counter DAI (C-DAI) for the scheduled PDSCH group. The DCI format may also include a total DAI (T-DAI) for at least one of the scheduled PDSCH group and a non-scheduled PDSCH group. When the DCI format includes a new feedback indicator field for at least one of the scheduled PDSCH group and the non-scheduled PDSCH group, the UE may multiplex HARQ-ACK bits only for PDSCH receptions for transmission in a PUCCH transmission occasion scheduled by the DCI format and may refrain from multiplexing HARQ-ACK bits for PDSCH receptions that are not scheduled by the DCI format. For HARQ-ACK retransmission, the UE may retransmit HARQ-ACK bits from more than one PDSCH group in the PUCCH transmission occasion.