HARQ-ACK Codebook Sizing for Carrier-Aggregated TDD Feedback
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Solution Overview
Problem
In existing LTE systems, the bit size of HARQ-ACKs (ACKs/NACKs) fed back by a user terminal is semi-statically determined, leading to mismatch between the number of configured and scheduled component carriers, resulting in unnecessary overhead and potential decoding errors due to differing recognition of codebook size between the user terminal and the radio base station.
Innovation Solution
Dynamic adjustment of the HARQ-ACK codebook size based on reported counter and total DAIs, allowing the user terminal to match the number of scheduled carriers, using counter DAIs for accumulative counts within bundling windows and total DAIs for overall counts, ensuring accurate feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the HARQ-ACK codebook size is semi-statically determined based on the number of configured component carriers, then the user terminal can maintain a fixed feedback structure, but the codebook size does not match the actual number of scheduled carriers, causing unnecessary overhead and potential decoding errors
Solution Approach 1:
The patent applies dynamics by making the HARQ-ACK codebook size variable rather than fixed. The codebook size is dynamically adjusted based on the actual number of scheduled component carriers in each downlink subframe. This is achieved through the base station transmitting DAI (Downlink Assignment Indicator) information that indicates the cumulative number of scheduled carriers, allowing the user terminal to determine the appropriate codebook size for each feedback instance, thus matching the feedback structure to the actual scheduling situation
Solution Approach 2:
The patent changes the parameter of codebook size from a semi-static configuration-based value to a dynamic value determined by the actual number of scheduled carriers. The DAI information serves as a parameter that directly controls the codebook size, enabling the system to adapt the feedback overhead to the actual data transmission requirements, reducing unnecessary feedback when fewer carriers are scheduled
2Ease of operation
If the codebook size is determined semi-statically, then the user terminal can simplify its determination process, but the radio base station and user terminal may have differing recognition of codebook size, leading to decoding errors
Solution Approach 1:
The patent implements feedback by having the base station transmit DAI (Downlink Assignment Indicator) information to the user terminal. This DAI information provides feedback about the actual number of scheduled component carriers, enabling the user terminal to adjust its codebook size determination accordingly. The feedback mechanism ensures both the base station and user terminal have consistent understanding of the codebook size, preventing decoding errors while maintaining operational simplicity
Solution Approach 2:
The DAI (Downlink Assignment Indicator) information acts as an intermediary between the base station's scheduling decisions and the user terminal's codebook size determination. This intermediary carries the necessary information about the number of scheduled carriers, allowing the user terminal to accurately determine the codebook size without complex calculations or assumptions, thus maintaining ease of operation while ensuring decoding accuracy
3Productivity
If carrier aggregation is expanded to include more component carriers, then the data rate can be increased, but the HARQ-ACK feedback overhead increases and codebook size mismatch becomes more likely
Solution Approach 1:
The patent applies dynamics by making the codebook size adaptable to the actual number of scheduled carriers rather than being fixed based on the maximum configured carriers. When carrier aggregation is expanded, the system can still maintain efficient feedback by dynamically adjusting the codebook size to match the actual scheduling needs, preventing feedback overhead from increasing proportionally with the number of configured carriers
Solution Approach 2:
The patent changes the codebook size parameter based on the actual scheduling situation. With expanded carrier aggregation, the DAI information enables the system to adjust the codebook size to reflect only the number of carriers that are actually scheduled for data transmission, rather than using a fixed size based on the maximum possible carriers, thus maintaining productivity benefits while controlling feedback overhead
Data Source
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Figure 3A~3B
AI summary
The present invention is designed so that it is possible to feed back HARQ-ACKs adequately even when a plurality of component carriers are configured in a radio communication system. The present invention provides a receiving section that receives DL signals transmitted from a plurality of component carriers (CCs), including CCs using TDD, and a control section that performs control so that HARQ-ACKs in response to the DL signals transmitted from the plurality of CCs based on a bundling window defined in TDD are transmitted in predetermined UL subframes, and the receiving section receives first information, which indicating the codebook size included in the downlink control information of each CC that is subject to DL transmission, and second information that indicates the counter values of CCs with DL assignments, in the bundling window, and the control section controls the transmission of HARQ-ACKs based on the first information and the second information.