Dynamic HARQ-ACK Codebook Sizing for LTE Carrier Aggregation
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Solution Overview
Problem
In LTE systems, the fixed codebook size for HARQ-ACK feedback leads to inefficient communication quality when the number of configured component carriers differs from the number of carriers scheduled in a subframe, causing recognition mismatches between user terminals and radio base stations, resulting in decreased communication quality.
Innovation Solution
A user terminal and radio base station system that dynamically controls the codebook size of HARQ-ACK feedback based on information about the cells scheduled, using downlink control information to adjust the bit size of ACK/NACK signals transmitted, ensuring proper decoding and maintaining communication quality even with multiple component carriers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the codebook size is fixedly determined based on the number of configured component carriers, then the user terminal can maintain a predetermined codebook size for HARQ-ACK feedback, but the codebook size becomes larger than necessary when fewer carriers are scheduled, leading to inefficient communication quality
Solution Approach 1:
The patent applies dynamics by enabling the codebook size to change dynamically based on the actual scheduling situation. The user terminal determines the codebook size according to the number of component carriers where downlink signals are actually scheduled in each subframe, rather than using a fixed size based on the maximum configured carriers. This dynamic adaptation ensures the codebook size matches the actual feedback needs, improving communication efficiency while maintaining reliability.
2Quantity of substance
If the codebook size is dynamically controlled based on received downlink signals, then the codebook size can be optimized to match the scheduled carriers, but recognition mismatches occur when the user terminal fails to detect downlink signals, leading to decoding failures at the radio base station
Solution Approach 1:
The patent implements feedback mechanisms through downlink control information (DCI) that includes indicators about the number of scheduled component carriers and their identities. The radio base station provides feedback to the user terminal about which carriers are scheduled, enabling the user terminal to accurately determine the codebook size without relying solely on its own detection. This feedback loop prevents recognition mismatches and ensures both ends agree on the codebook size for proper HARQ-ACK decoding.
Solution Approach 2:
The patent uses downlink control information as an intermediary to convey scheduling information between the radio base station and user terminal. The DCI includes specific fields that indicate the number of scheduled carriers and their identities, serving as a mediator that resolves potential recognition mismatches. This intermediary mechanism ensures that even if the user terminal fails to detect certain downlink signals, it can still determine the correct codebook size based on the control information provided by the base station.
3Adaptability or versatility
If the number of configured component carriers is expanded beyond 5 in LTE Rel. 13 and later versions, then the system can support more carriers for carrier aggregation, but the difference between configured and scheduled carrier numbers increases significantly, exacerbating the codebook size inefficiency problem
Solution Approach 1:
The patent applies dynamics by enabling the codebook size to change dynamically based on the actual scheduling situation. The user terminal determines the codebook size according to the number of component carriers where downlink signals are actually scheduled in each subframe, rather than using a fixed size based on the maximum configured carriers. This dynamic adaptation ensures the codebook size matches the actual feedback needs, improving communication efficiency while maintaining reliability.
Data Source
AI summary
A user terminal is disclosed including a transmitter that transmits delivery acknowledgment signals (ACK/NACK) in response to downlink (DL) signals transmitted from a plurality of cells, a receiver that receives information about cells to be scheduled, and a processor that controls transmission of the ACK/NACK based on the information about the cells to be scheduled. Further, a radio base station is disclosed that communicates with a user terminal using a plurality cells, the radio base station including a processor that controls scheduling of downlink (DL) signals transmitted respectively from the plurality of cells; a transmitter that transmits information about cells to be scheduled; and a receiver that receives delivery acknowledgement signals (ACK/NACK) transmitted from the user terminal based on the information about the cells to be scheduled.