Dynamic HARQ-ACK Codebook Adjustment for LTE Carrier Aggregation
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Solution Overview
Problem
In existing LTE systems, the bit size of ACKs/NACKs (codebook size) is semi-statically determined and fixed based on the number of configured component carriers, leading to inefficient overhead and potential communication quality issues when the number of scheduled carriers differs from the configured carriers, especially with the expected increase in configurable carriers in later versions.
Innovation Solution
A user terminal dynamically determines the HARQ-ACK codebook size based on the number of cells receiving downlink signals, using a bundling window defined in TDD as a grid of subframes and HARQ-ACK codebook indicators (HCIs) to adjust the number of HARQ-ACK bits transmitted, ensuring accurate feedback even with multiple component carriers.
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 feedback structure is simple and reliable, but the overhead becomes inefficient when the number of scheduled carriers differs from configured carriers
Solution Approach 1:
The patent applies dynamics by transitioning from a semi-static codebook size determination to a dynamic one. The codebook size is now determined based on the actual number of scheduled component carriers rather than pre-configured carriers, allowing the feedback structure to adapt to varying scheduling conditions and reduce overhead when fewer carriers are scheduled.
Solution Approach 2:
The patent changes the parameter used for codebook size determination from the number of configured carriers to the number of scheduled carriers. This parameter change enables the system to adjust the codebook size according to actual scheduling needs, improving overhead efficiency while maintaining feedback reliability through proper indication mechanisms.
2Device complexity
If the HARQ-ACK codebook size is fixed based on configured carriers, then the system structure is simple, but mismatch recognition between user terminal and radio base station occurs when scheduled carriers differ from configured carriers
Solution Approach 1:
The patent introduces feedback mechanisms through HARQ-ACK codebook indicators (HCIs) that are transmitted in downlink assignments. These indicators provide feedback information about the actual number of scheduled carriers to the user terminal, enabling accurate codebook size determination and preventing mismatch recognition issues while maintaining relatively simple system structure.
Solution Approach 2:
The patent uses HCIs as intermediary elements that mediate between the radio base station's scheduling decisions and the user terminal's codebook construction. These indicators serve as a communication bridge that ensures both sides have consistent understanding of the actual number of scheduled carriers, eliminating information loss without significantly complicating the overall system structure.
3Adaptability or versatility
If the number of configurable carriers is increased in later LTE versions, then the system capacity increases, but the fixed codebook size approach becomes increasingly inefficient
Solution Approach 1:
The patent makes the codebook size determination dynamic to match the increasing flexibility of carrier aggregation. By determining codebook size based on the actual number of scheduled carriers rather than configured carriers, the system can efficiently handle varying numbers of carriers from a small number up to 32, adapting the feedback structure to actual usage patterns and reducing overhead as the system scales.
Data Source
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AI summary
The present invention is designed so that HARQ-ACKs can be fed back 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 cells that apply TDD, and a control section that performs control to transmit in a predetermined UL subframe HARQ-ACKs for the DL signals transmitted from a plurality of cells based on a bundling window defined in TDD, and the control section determines a cell whose HARQ-ACK is to be transmitted based on HARQ-ACK codebook indicators (HCIs) transmitted in each subframe in the bundling window.