Dynamic HARQ Feedback Disabling in NR V2X Sidelink
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Solution Overview
Problem
In NR V2X communication, there is a need to prevent unnecessary HARQ feedback transmission and reception between User Equipments (UEs) to conserve power.
Innovation Solution
A method where a first device obtains a MAC PDU with enabled HARQ feedback, transmits sidelink control information (SCI) with HARQ feedback enabled, performs (N−1)-th transmission of the MAC PDU, and then transmits SCI with HARQ feedback disabled upon failure of the (N−1)-th transmission, with N being the maximum number of transmissions for the MAC PDU.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If HARQ feedback is continuously transmitted and received between UEs in NR V2X communication, then communication reliability is improved, but power consumption increases
Solution Approach 1:
The patent implements dynamic HARQ feedback disabling by transitioning from enabled to disabled state based on transmission attempts. The transmitting UE disables HARQ feedback after a certain number of failed transmission attempts (e.g., 3 attempts), making the feedback mechanism adaptive rather than static. This dynamic adjustment resolves the contradiction by maintaining feedback for reliable communications while eliminating it when communications are failing, thus saving power without sacrificing reliability when needed.
Solution Approach 2:
The patent changes the parameter of HARQ feedback status from a fixed enabled state to a variable state that can switch between enabled and disabled. By modifying this parameter based on transmission outcomes (using indicators like NDI or explicit feedback disable indicators), the system optimizes the balance between reliability and power consumption. The feedback mechanism adapts its operation mode based on channel conditions and transmission success rates.
2Reliability
If HARQ feedback transmission is maintained for all MAC PDU transmissions, then transmission reliability is improved, but unnecessary feedback increases power consumption
Solution Approach 1:
The patent extracts HARQ feedback transmission from the continuous operation mode and removes it selectively based on transmission attempts. By taking out the feedback mechanism only when it becomes unnecessary (after maximum retransmission attempts are reached or failures are detected), the system eliminates energy waste from unnecessary feedback while preserving reliability during the initial transmission phase when feedback is still valuable.
3Reliability
If the transmitting UE continues to request HARQ feedback for each transmission, then error correction capability is improved, but communication overhead increases
Solution Approach 1:
The patent implements periodic reassessment of HARQ feedback necessity rather than continuous requests. The transmitting UE periodically evaluates whether to maintain feedback requests based on transmission outcomes and predefined thresholds. This periodic action reduces overhead by spacing out feedback requests appropriately while maintaining error correction capability during periods when feedback is actually beneficial.
Data Source
AI summary
Provided are a method for a first device to perform wireless communication, and a device for supporting same. The method includes the steps of: generating a medium access control protocol data unit (MAC PDU) in which a hybrid automatic repeat request (HARQ) feedback is enabled; transmitting sidelink control information (SCI) including information related to the enabling of the HARQ feedback for the MAC PDU to a second device; performing an (N−1)-th transmission of the MAC PDU on the second device; transmitting SCI including information related to the disabling of the HARQ feedback for the MAC PDU to the second device; and performing an N-th transmission of the MAC PDU on the second device, wherein N may be the maximum number of transmissions related to MAC PDU.