HARQ-ACK Codebook Sizing via DAI Fields in Carrier Aggregation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In wireless communication systems supporting carrier aggregation, there is a challenge in accurately determining the size of the HARQ-ACK codebook, which is dynamic and changes due to varying downlink data channels, leading to potential misalignment between the UE and eNB, affecting reliable uplink transmission and downlink data performance.
Innovation Solution
The system employs an accumulated downlink assignment indicator (A-DAI) and total DAI (T-DAI) fields in downlink and uplink grants to determine the size of the HARQ-ACK codebook, ensuring both the UE and eNB can accurately recognize and manage the codebook size, thereby optimizing HARQ operations and reducing overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of serving cells is increased to support higher data rates, then the system capacity and throughput are improved, but the complexity of HARQ-ACK codebook management increases and alignment between UE and eNB becomes more difficult
Solution Approach 1:
The patent segments the HARQ-ACK feedback by introducing separate DAI (Downlink Assignment Indicator) fields for different serving cells and groups. The A-DAI (Accumulated DAI) and T-DAI (Total DAI) fields divide the codebook management into manageable segments, allowing independent tracking of downlink assignments across multiple serving cells. This segmentation enables the UE to construct the HARQ-ACK codebook in an organized manner even when many serving cells are aggregated.
Solution Approach 2:
The patent implements a feedback mechanism where the eNB transmits DAI information in downlink grants, and the UE uses this feedback to dynamically adjust its HARQ-ACK codebook construction. The A-DAI provides cumulative feedback about the number of downlink assignments, while T-DAI provides total assignment information. This feedback loop ensures both UE and eNB maintain consistent understanding of the codebook size and content, enabling reliable HARQ operations in carrier aggregation scenarios.
2Productivity
If dynamic HARQ-ACK codebook size is used to adapt to varying downlink data channels, then the overhead is reduced and efficiency is improved, but the risk of misalignment between UE and eNB increases
Solution Approach 1:
The patent applies preliminary action by having the eNB pre-configure the UE with DAI parameters and codebook construction rules before actual HARQ operations begin. The eNB transmits configuration information including DAI field formats, codebook sizing rules, and mapping relationships in advance. This preliminary configuration ensures that when dynamic codebook size changes occur, both UE and eNB already have the necessary information to maintain alignment without requiring real-time negotiation.
Solution Approach 2:
The patent uses feedback mechanisms where the eNB monitors HARQ-ACK reception and adjusts downlink grant transmissions accordingly. The DAI fields provide continuous feedback about the state of downlink assignments, allowing the UE to dynamically adjust its codebook size while maintaining synchronization with the eNB. This feedback-driven adaptation enables efficient overhead management while preserving reliability through consistent UE-eNB understanding of the current codebook state.
3Reliability
If a larger number of HARQ ACKs are transmitted to cover more downlink data channels, then the coverage and reliability are improved, but the uplink control overhead increases
Solution Approach 1:
The patent merges multiple HARQ-ACK bits into a compact codebook structure that can be efficiently transmitted. Instead of sending separate ACK/NACK signals for each downlink data channel, the patent combines them into a unified HARQ-ACK codebook with a dynamically determined size. The DAI fields enable this merging by providing compact representation of multiple downlink assignments, reducing the total number of uplink control bits needed while maintaining complete coverage of all downlink channels.
Solution Approach 2:
The patent changes the parameter of codebook size dynamically based on the actual number of downlink assignments. Rather than using a fixed maximum size that would always accommodate all possible serving cells, the codebook size adapts to the current transmission scenario. The DAI fields drive this parameter change by informing the UE of the actual number of downlink assignments, allowing the HARQ-ACK overhead to scale with the actual traffic load rather than the maximum potential load.
Data Source
AI summary
Provided is a method of performing HARQ by a UE in a wireless communication system that supports carrier aggregation (CA). The method includes: receiving, from an evolved nodeB (eNB), a downlink grant on a first Physical Downlink Control Channel (PDCCH), the downlink grant including an accumulated downlink assignment indicator (A-DAI) field and a total DAI (T-DAI) field; receiving a first PDSCH indicated by the first PDCCH, the first PDSCH being transmitted from the eNB; receiving, from the eNB, an uplink grant on a second PDCCH, the uplink grant indicating a transmission of a Physical Uplink Shared Channel (PUSCH); determining a size of a HARQ-ACK codebook to which a HARQ-ACK with respect to the first PDSCH is to be mapped, based on the A-DAI and the T-DAI; and transmitting, to the eNB, the HARQ-ACK with respect to the first PDSCH on the PUSCH.