HARQ-ACK Feedback Window for Unlicensed Spectrum Reliability
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Solution Overview
Problem
HARQ-ACK codebook transmission on unlicensed spectrum faces challenges due to the failure of Listen Before Talk (LBT) procedures, leading to unreliable transmission and potential resource waste.
Innovation Solution
Implementing a HARQ-ACK codebook feedback window with multiple consecutive or non-consecutive slots, allowing the UE to transmit the HARQ-ACK codebook within this window after successful LBT, and optionally repeating transmissions if LBT fails initially.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If LBT procedure is performed before transmission on unlicensed spectrum, then channel access fairness is improved, but transmission reliability deteriorates due to LBT failure
Solution Approach 1:
The gNB performs LBT procedure in advance to acquire Channel Occupancy Time (COT) before scheduling downlink transmissions. This preliminary action ensures that the gNB has secured the channel resources beforehand, allowing it to guarantee transmission opportunities for HARQ-ACK feedback without requiring the UE to perform separate LBT procedures, thereby improving transmission reliability while maintaining channel access fairness.
2Reliability
If multiple transmission opportunities are provided for HARQ-ACK codebook, then transmission reliability is improved, but resource waste increases due to unused transmission slots
Solution Approach 1:
The system dynamically adjusts the number of HARQ-ACK transmission opportunities based on the actual COT duration and channel conditions. The gNB configures the feedback window size and transmission opportunities adaptively according to the available channel resources, ensuring that multiple transmission opportunities are provided only when channel conditions permit, thereby improving reliability without causing excessive resource waste.
3Reliability
If HARQ-ACK codebook is transmitted in every available slot within feedback window, then transmission reliability is improved, but device complexity increases due to multiple LBT attempts
Solution Approach 1:
The gNB's COT acquisition serves multiple functions: it simultaneously provides channel access for downlink transmissions and guarantees uplink transmission opportunities for HARQ-ACK feedback. This multi-functionality eliminates the need for separate LBT procedures at the UE side for each transmission opportunity, reducing device complexity while maintaining high transmission reliability through the configured feedback window.
Data Source
AI summary
Methods and apparatuses for HARQ-ACK code book transmission on unlicensed spectrum are disclosed. 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 first message indicating a first candidate opportunity for transmission of a Hybrid Automatic Repeat Request-Acknowledgement (HARQ-ACK) code book corresponding to the one or multiple downlink transmissions and a second message indicating a number of allowed opportunities for transmission of the HARQ-ACK codebook; a processor that determines the HARQ-ACK codebook and a number of total candidate opportunities for transmission of the HARQ-ACK codebook; and a transmitter that, in response to a channel access for the first candidate opportunity being successful, transmits the HARQ-ACK codebook in the first candidate opportunity, and, in response to the channel access for the first candidate opportunity being failed and the number of the total candidate opportunities being larger than one, attempts to transmit the HARQ-ACK codebook in a second candidate opportunity.