HARQ Buffer Management for Configured Grant Retransmissions
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Solution Overview
Problem
In wireless communication systems, particularly in 3GPP LTE and NR, there is a challenge in efficiently managing hybrid automatic repeat request (HARQ) transmissions for configured grants (CGs), leading to unnecessary allocation of retransmission resources and inefficient handling of HARQ buffers, especially in scenarios involving vehicle-to-everything (V2X) communications.
Innovation Solution
A method and apparatus are provided to perform retransmissions of data units using a retransmission resource for a HARQ process ID based on the number of transmissions not reaching a maximum, and to flush the HARQ buffer in a sidelink process when the maximum number of transmissions is reached, ensuring proper resource allocation and management for HARQ processes using configured grants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If retransmission resources are allocated for configured grants, then reliability of data transmission is improved, but device complexity and resource management overhead increase
Solution Approach 1:
The patent segments the HARQ buffer management by introducing separate indicators (first indicator and second indicator) for different CG-DAI values. When the first CG-DAI equals the second CG-DAI, one HARQ buffer management approach is applied; when they differ, a different approach is used. This segmentation resolves the contradiction by providing granular control over buffer management based on specific transmission conditions, improving reliability without uniformly increasing complexity across all scenarios.
Solution Approach 2:
The patent changes the parameter of CG-DAI (Configured Grant Downlink Assignment Index) to trigger different HARQ buffer management behaviors. By monitoring whether the first CG-DAI equals the second CG-DAI, the system dynamically adjusts buffer flushing decisions. This parameter-based control mechanism improves transmission reliability through appropriate retransmission handling while avoiding unnecessary buffer management complexity in cases where CG-DAI values match.
2Loss of energy
If maximum number of transmissions is enforced, then resource waste is reduced, but loss of information may occur in HARQ buffer
Solution Approach 1:
The patent implements a feedback mechanism through CG-DAI indicators that provide information about the transmission state to the receiving device. The receiving device uses the comparison between first and second CG-DAI values to determine whether to flush the HARQ buffer. This feedback-based approach ensures that resources are not wasted on unnecessary retransmissions (when CG-DAI values are equal) while preserving information in the buffer only when actually needed (when CG-DAI values differ), thus resolving the contradiction between resource efficiency and information preservation.
Solution Approach 2:
The patent performs preliminary buffer management actions based on predicted transmission outcomes. By evaluating CG-DAI values before actual retransmission occurs, the system can proactively flush the HARQ buffer when the first CG-DAI equals the second CG-DAI, preventing potential resource waste. Conversely, when CG-DAI values differ, the buffer is preserved in advance. This preliminary action approach resolves the contradiction by making informed decisions before resource consumption or information loss can occur.
Data Source
AI summary
A method and apparatus for hybrid automatic repeat request (HARQ) transmissions for configured grants (CGs) in a wireless communication system is provided. A first wireless device receives a retransmission resource for a HARQ process identifier (ID) for a CG. When a number of transmissions of a media access control (MAC) protocol data unit (PDU) does not reach to a maximum number of transmissions, the first wireless device performs retransmission of the MAC PDU to a second wireless device by using the retransmission resource. When the number of transmissions of the MAC PDU reaches to the maximum number of transmissions, the first wireless device flushes a HARQ buffer in a sidelink process.