Adjusting Contention Window Size via HARQ-ACK Feedback
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Solution Overview
Problem
Wireless access systems supporting unlicensed bands face inefficiencies in data transmission and channel access procedures, particularly in adjusting contention window sizes and determining the validity of HARQ-ACK information, which affects the overall performance and balance with licensed band operations.
Innovation Solution
A method for adjusting the contention window size (CWS) in wireless access systems by performing a channel access procedure, transmitting a downlink signal, and receiving HARQ-ACK information, with adjustments based on the feedback to optimize CWS settings, including separate counting for each codeword and setting the CWS for each priority class, and increasing it if the HARQ-ACK probability is high.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the contention window size is adjusted based on HARQ-ACK information in unlicensed bands, then channel access efficiency is improved, but system complexity increases due to additional feedback processing requirements
Solution Approach 1:
The patent adjusts the contention window size (CWS) parameter based on HARQ-ACK feedback information. When NACK probability exceeds a threshold, CWS is increased to reduce collision probability; when ACK probability is high, CWS is decreased to improve channel access efficiency. This dynamic parameter adjustment resolves the contradiction by adapting system behavior to actual channel conditions.
Solution Approach 2:
The patent implements a feedback mechanism where HARQ-ACK information from previous transmissions is used to adjust future channel access parameters. The base station monitors NACK/ACK ratios and adjusts CWS accordingly, creating a closed-loop control system that improves channel access efficiency while managing complexity through standardized feedback processing.
2Adaptability or versatility
If separate CWS adjustment is performed for each priority class, then service differentiation is improved, but control complexity increases
Solution Approach 1:
The patent divides the contention window adjustment mechanism into separate priority classes (priority 0-3), allowing independent CWS adjustment for each class based on their specific QoS requirements. High-priority traffic can maintain smaller CWS values for faster access, while low-priority traffic uses larger CWS values, achieving service differentiation through segmentation of the control mechanism.
Solution Approach 2:
Different contention window parameters are applied to different priority classes based on their local quality requirements. Each priority class has its own CWS configuration that reflects its specific service needs, allowing optimized performance for each traffic type without requiring complex global control mechanisms.
3Reliability
If contention window size is increased to reduce collision probability, then channel access reliability is improved, but channel access speed decreases
Solution Approach 1:
The patent implements dynamic CWS adjustment where the contention window size changes based on real-time channel conditions and HARQ-ACK feedback. When collisions are detected (high NACK rate), CWS is increased to improve reliability; when channel conditions are good (high ACK rate), CWS is decreased to maintain fast access speed. This dynamic adaptation resolves the contradiction by making the system flexible rather than static.
Solution Approach 2:
The contention window size parameter is adjusted in response to changing channel conditions. The system monitors HARQ-ACK feedback and modifies CWS values to balance reliability and speed requirements, using parameter changes to adapt to different operational scenarios rather than maintaining a fixed value.
Data Source
AI summary
The present invention relates to a wireless access system that supports an unlicensed band, and provides various methods for adjusting a contention window size and devices for supporting the same. As an embodiment of the present invention, a method for adjusting a contention window size (CWS) in a wireless access system supporting an unlicensed band may comprise the steps of: performing a channel access procedure; when, as a result of performing the channel access procedure, it is determined that a serving cell (Scell) in the unlicensed band is in an idle state, transmitting a transmission burst including a downlink signal; receiving HARQ-ACK information corresponding to the transmission burst; and adjusting the CWS on the basis of the HARQ-ACK information corresponding to the first subframe of the transmission burst.