HARQ-ACK Feedback Mapping for Unlicensed Carrier Timing
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Solution Overview
Problem
In LTE Release-14 systems, the transmission of uplink control signals on unlicensed bands is challenging due to the dynamic nature of uplink-downlink configurations, leading to uncertainties in HARQ-ACK feedback timing, which affects the efficiency of data transmission.
Innovation Solution
A method for feeding back HARQ-ACK information involves determining a second uplink subframe for feedback, selecting an appropriate uplink carrier, and mapping HARQ-ACK bits based on downlink assignment indices, allowing for flexible and adaptive HARQ-ACK feedback even on unlicensed carriers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If uplink control signals are transmitted on unlicensed bands with dynamic uplink-downlink configurations, then spectrum utilization is improved, but HARQ-ACK feedback timing becomes uncertain
Solution Approach 1:
The patent applies preliminary action by pre-configuring multiple uplink subframes and establishing predetermined mapping relationships between downlink subframes and uplink feedback subframes before actual transmission occurs. This allows the system to prepare multiple potential feedback paths in advance, so when channel conditions change dynamically, the UE can quickly determine which pre-configured uplink subframe to use for HARQ-ACK feedback, eliminating timing uncertainty without sacrificing spectrum utilization flexibility
2Adaptability or versatility
If HARQ-ACK feedback timing is made flexible to adapt to dynamic channel conditions, then system adaptability is improved, but feedback timing uncertainty increases
Solution Approach 1:
The patent implements dynamics by configuring multiple uplink subframes with different timing relationships and allowing the system to dynamically select the appropriate feedback timing based on actual channel conditions. The base station can indicate through downlink control information which specific uplink subframe should be used for feedback, enabling flexible adaptation to varying channel states while maintaining deterministic timing through explicit signaling
Solution Approach 2:
The patent applies feedback principles by establishing a closed-loop mechanism where the base station monitors channel conditions and sends indications to the UE about which uplink subframe to use for HARQ-ACK feedback. This feedback loop ensures that the system adapts to dynamic channel conditions while maintaining timing certainty through explicit base station guidance rather than leaving the UE to independently determine feedback timing
3Reliability
If multiple uplink subframes are configured for HARQ-ACK feedback, then feedback reliability is improved, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the uplink resources into multiple distinct uplink subframes, each with specific timing relationships to downlink subframes. Instead of using a single complex feedback mechanism, the system segments the feedback opportunity into multiple simpler, pre-configured options. The UE only needs to identify which segment (uplink subframe) to use based on simple comparison logic, reducing overall device complexity while improving reliability through multiple potential feedback paths
Data Source
AI summary
The present disclosure provides a method for feeding back HARQ-ACK information. In the method provided by the present disclosure, a UE receives DL-GRANT scheduling downlink HARQ transmission in a time-frequency bundling window corresponding to respective uplink subframe for feeding back HARQ-ACK in turn, obtains a DL DAI in the DL-GRANT, and determines a mapping value of each DL DAI; then, maps bundling window corresponding to respective uplink subframe for feeding back the HARQ-ACK to corresponding bits of a feedback bit sequence according to the mapping value of the DL DAI; and transmits the HARQ-ACK on an available uplink carrier.