Sidelink Channel Access Using HARQ-ACK Ratios for Dynamic CW Control
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Solution Overview
Problem
The challenge in 5G communication systems is to efficiently manage channel access in sidelink communication over unlicensed bands, ensuring fair use and minimizing interference among multiple systems.
Innovation Solution
A method for a transmitting terminal to adjust the contention window (CW) based on hybrid automatic repeat request-acknowledgement (HARQ-ACK) feedbacks, calculating an ACK or NACK ratio and comparing it to a configured threshold to optimize channel occupancy time (COT) for groupcast sidelink transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If channel access procedure is implemented in unlicensed band for sidelink communication, then fairness in using unlicensed band is ensured, but channel access efficiency deteriorates
Solution Approach 1:
The patent implements HARQ-ACK feedback mechanism where receiving terminals send acknowledgment information back to the transmitting terminal. The transmitting terminal uses this feedback to calculate ACK ratio and dynamically adjust CW size, creating a closed-loop control system that optimizes channel access efficiency while maintaining fairness through feedback-driven adaptation
Solution Approach 2:
The patent makes the CW size dynamic by allowing it to change based on ACK ratio and transmission conditions. The CW can be increased or decreased according to the actual channel access performance, transforming the static channel access parameters into adaptive ones that respond to real-time feedback, thereby improving efficiency while maintaining fairness
2Reliability
If CW size is increased to ensure fairness in unlicensed band, then channel access efficiency for new terminals deteriorates
Solution Approach 1:
The patent implements dynamic CW adjustment where the CW size changes based on ACK ratio and transmission conditions. When transmission is successful (high ACK ratio), CW is reduced to allow faster access for new terminals. When transmission fails (low ACK ratio), CW is increased to ensure fairness and prevent continuous access by problematic terminals, thus balancing fairness and access speed
Solution Approach 2:
The patent changes the CW parameter dynamically based on measured performance metrics (ACK ratio). By adjusting CW size according to actual transmission outcomes, the system can reduce CW when conditions are good (improving access speed) and increase CW when conditions are poor (ensuring fairness), resolving the contradiction between fairness and access time
3Reliability
If HARQ-ACK feedback is enabled for groupcast SL transmission, then communication reliability is improved, but device complexity increases
Solution Approach 1:
The patent enables HARQ-ACK feedback for groupcast SL transmission to improve communication reliability. The feedback mechanism allows the transmitting terminal to ascertain whether group members received data correctly, enabling retransmission when necessary and thus enhancing reliability through systematic feedback utilization
Solution Approach 2:
The patent manages feedback processing complexity by introducing a ratio threshold parameter and ACK ratio calculation. Instead of processing every individual feedback signal in detail, the system aggregates feedback into an ACK ratio and uses this summarized metric to trigger CW adjustment, simplifying the processing complexity while maintaining the reliability benefits of feedback
Data Source
AI summary
A method and a device for channel access in sidelink communication are disclosed. A method of a first terminal comprises the steps of: initiating a COT; performing groupcast SL transmission within the COT; receiving one or more HARQ-ACK feedbacks for the groupcast SL transmission; when a ratio threshold is configured for the first terminal, calculating an ACK ratio on the basis of the one or more HARQ-ACK feedbacks; and adjusting a CW on the basis of a result of comparison between the ACK ratio and the ratio threshold.