HARQ-ACK Feedback Mapping for Carrier Aggregation Efficiency
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Solution Overview
Problem
The existing HARQ-ACK feedback mechanism in LTE systems is inefficient for supporting downlink carrier aggregation with up to 32 carriers, leading to a decrease in downlink peak rate due to the inclusion of unnecessary HARQ-ACK bits.
Innovation Solution
A method and apparatus for HARQ-ACK information feedback that involves determining a time-frequency bundling window, receiving a downlink grant, and mapping HARQ-ACK bits to a feedback bit sequence based on a downlink assignment index, effectively removing invalid bits and optimizing the feedback process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the existing HARQ-ACK feedback mechanism is used in downlink carrier aggregation with 32 carriers, then the system supports a large number of carriers, but the feedback efficiency decreases due to inclusion of unnecessary HARQ-ACK bits
Solution Approach 1:
The patent extracts and removes unnecessary HARQ-ACK bits from the feedback sequence by identifying which downlink subframes actually contain data transmissions. The UL DAI parameter is used to indicate the actual number of downlink subframes with transmissions, allowing the UE to exclude corresponding unnecessary ACK/NACK bits from the uplink feedback, thereby improving feedback efficiency while maintaining support for 32 carriers
Solution Approach 2:
The patent changes the parameter representation by introducing UL DAI (Uplink Downlink Assignment Index) to dynamically indicate the actual number of downlink subframes containing transmissions. This parameter change allows the system to adapt the feedback sequence length according to actual transmission conditions, resolving the contradiction between supporting many carriers and maintaining feedback efficiency
2Reliability
If HARQ-ACK bits are included for all downlink subframes in the time-frequency bundling window, then the feedback is comprehensive, but unnecessary bits reduce the downlink peak rate
Solution Approach 1:
The patent extracts only the necessary HARQ-ACK bits corresponding to downlink subframes that actually contain data transmissions. By using UL DAI to indicate the actual number of transmitted subframes, the system removes unnecessary ACK/NACK bits for subframes without transmissions, maintaining feedback reliability for actual data while improving downlink peak rate by reducing overhead
Solution Approach 2:
Instead of providing feedback for all possible downlink subframes in the bundling window, the patent applies partial action by providing feedback only for the actual number of subframes containing transmissions as indicated by UL DAI. This partial feedback approach maintains sufficient reliability for actual data transmissions while avoiding the excessive overhead that would reduce peak rate
Data Source
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AI summary
An apparatus and method for feeding back hybrid automatic repeat request-acknowledgement (HARQ-ACK) information are provided. The apparatus and method include user equipment (UE) that first receives a downlink grant (DL-GRANT) which schedules downlink HARQ transmission in a time-frequency bundling window corresponding to an uplink subframe used for feeding back HARQ-ACK, obtains a DL downlink assignment index (DL DAI) in the DL-GRANT, and determines a mapping value of each DL DAI. Then, according to the mapping value of the corresponding DL DAI, the HARQ-ACK bit of each HARQ feedback unit is mapped to a corresponding bit of a feedback bit sequence. According to the method and apparatus provided by the present disclosure, useless HARQ-ACK bits may be effectively removed, and efficiency for feeding back HARQ-ACK may be increased. As such, a downlink peak rate of a UE is ensured.