Dynamic Contention Window Adjustment for Sidelink Groupcast HARQ Feedback
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Solution Overview
Problem
Current contention window size adjustment procedures for sidelink groupcast in wireless networks are inadequate, particularly for groupcast or multicast traffic, as they do not effectively consider different HARQ feedback types, leading to inefficiencies in channel access and data transmission.
Innovation Solution
The proposed solution involves a processor-based system that transmits and receives physical shared control channels and hybrid automatic repeat request (HARQ) feedback to determine a contention window size adjustment for sidelink groupcast, using HARQ feedback options 1 and 2 to adjust the contention window based on ACK/NACK feedback from group member UEs within a reference duration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed contention window size is used for sidelink groupcast, then the device complexity is reduced, but the transmission reliability deteriorates due to inability to adapt to varying channel conditions and HARQ feedback
Solution Approach 1:
The contention window size is made dynamic rather than fixed. The transmitting UE adjusts the contention window size based on HARQ feedback received from group member UEs within a reference duration. When NACK feedback is received, the contention window size is increased to reduce collision probability; when ACK feedback is received, the contention window size is decreased to improve channel access efficiency. This dynamic adaptation resolves the contradiction by allowing the system to maintain reliability through adaptability while managing complexity through rule-based adjustments.
Solution Approach 2:
The system implements a feedback mechanism where group member UEs send HARQ feedback (ACK/NACK) to the transmitting UE. The transmitting UE uses this feedback information within a reference duration to adjust the contention window size for subsequent groupcast transmissions. This feedback loop enables the system to adapt to channel conditions and transmission success rates, improving reliability while the adjustment rules keep the complexity manageable.
2Reliability
If the contention window size is increased to reduce collisions, then the transmission reliability improves, but the channel access efficiency deteriorates due to longer waiting times
Solution Approach 1:
The contention window size dynamically adapts based on actual transmission outcomes rather than being statically increased. When transmissions are successful (ACK feedback), the contention window size is decreased to allow faster channel access and improve efficiency. When collisions occur (NACK feedback), the size is increased to reduce collision probability. This dynamic behavior resolves the contradiction by only increasing the window size when necessary for collision avoidance while maintaining efficiency during good channel conditions.
Solution Approach 2:
The system changes the contention window size parameter based on HARQ feedback outcomes. The parameter is adjusted within a reference duration according to the ratio of NACK to ACK feedback received from group member UEs. This parameter adaptation allows the system to balance between collision avoidance (reliability) and channel access speed (efficiency) by modifying the contention window size to match current channel conditions.
3Reliability
If HARQ feedback from all group member UEs is considered, then the transmission reliability improves, but the processing complexity increases due to multiple feedback sources
Solution Approach 1:
The system processes HARQ feedback from group member UEs within a specific reference duration window rather than considering all feedback indefinitely. This temporal localization allows the transmitting UE to focus on recent feedback information that is most relevant to current channel conditions, improving reliability through comprehensive yet focused feedback analysis while managing complexity by limiting the processing window.
Solution Approach 2:
The system considers HARQ feedback from group member UEs within a reference duration, which may be less than the total possible feedback sources. This partial consideration of feedback (limited to a reference duration) provides sufficient information for reliable contention window adjustment without the excessive complexity of processing all possible feedback from all group members indefinitely. The reference duration acts as a practical boundary that balances comprehensiveness with complexity.
Data Source
AI summary
Apparatuses, methods, and systems are disclosed for contention window size adjustment procedure for sidelink groupcast. An apparatus (500) includes a processor (505) and memory (510). The processor (505) is configured to transmit physical shared control channel (“PSCCH”) and physical shared sidelink channel (“PSSCH”) corresponding to groupcast data transmission. The processor (505) is configured to receive physical shared feedback channel (“PSFCH”) containing hybrid automatic repeat request (“HARQ”) feedback after a predetermined number of slots for a corresponding groupcast transmission. The processor (505) is configured to determine a contention window size adjustment for a groupcast PSSCH based on the transmitted groupcast HARQ feedback associated with PSSCH within a reference duration.