Dynamic Contention Window Adjustment for 5G Unlicensed Channel Access
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Solution Overview
Problem
Current wireless communication systems face challenges in efficiently performing channel access procedures, particularly in unlicensed bands, due to the lack of effective methods for determining idle states and optimizing contention windows, which affects data transmission reliability and efficiency.
Innovation Solution
A method and apparatus for a base station and terminal in a wireless communication system that determine a contention window based on HARQ-ACK feedbacks for physical downlink shared channels, allowing for channel sensing and idle state determination, enabling efficient downlink or uplink signal transmission by identifying whether a sub-band is idle through a defer duration and reference duration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If contention window size is increased to reduce collisions in unlicensed bands, then transmission reliability is improved, but channel access delay increases
Solution Approach 1:
The contention window size is made dynamic rather than fixed. The base station adjusts the contention window size based on channel conditions and transmission outcomes. When collisions are detected or channel conditions deteriorate, the contention window size is increased to reduce collision probability. When channel conditions are good, the size is reduced to minimize access delay, thus adapting the parameter to current system state.
Solution Approach 2:
The system implements feedback mechanisms where transmission outcomes (ACK/NACK) are monitored and used to adjust the contention window size. The base station receives feedback about successful or failed transmissions and dynamically modifies the contention window parameters for subsequent channel access attempts, creating a closed-loop control system that balances reliability and delay.
2Reliability
If channel sensing duration is extended to accurately determine idle state, then channel access reliability is improved, but channel access efficiency deteriorates
Solution Approach 1:
The system performs channel sensing for a duration that is sufficient to achieve required reliability but not excessively long. The sensing duration is optimized to capture enough channel state information to make reliable idle/busy decisions while minimizing the time spent before potential transmission. This avoids both insufficient sensing (low reliability) and excessive sensing (low efficiency).
Solution Approach 2:
The channel sensing parameters including duration and threshold values are dynamically adjusted based on channel conditions and traffic requirements. When channel conditions are stable, shorter sensing durations are used. When conditions are volatile or uncertain, sensing duration is extended to ensure reliable detection, thus adapting the parameter to current environmental conditions.
3Productivity
If contention window adjustment is performed frequently to optimize transmission, then data transmission rate is improved, but system complexity increases
Solution Approach 1:
The contention window adjustment is performed periodically based on transmission outcomes rather than continuously. After each channel access attempt or at regular intervals, the system evaluates transmission success and adjusts the contention window size accordingly. This periodic adjustment mechanism achieves good transmission rates through frequent optimization while avoiding the excessive complexity of continuous real-time adjustment.
Data Source
AI summary
The disclosure relates to a communication method and system for converging a 5G communication system for supporting higher data rates beyond a 4G system with a technology for IoT. A method of a base station includes determining a contention window for a sub-band among multiple sub-bands based on hybrid automatic repeat request-acknowledgement feedbacks corresponding to physical downlink shared channels (PDSCHs) in a reference duration, identifying a number for the sub-band between zero and the contention window, sensing the sub-band based on the number and a defer duration, and performing a downlink transmission based on sensing the sub-band to be idle, wherein the reference duration starts from a beginning of a channel occupancy and ends at a first slot where at least one of the PDSCHs is transmitted, and wherein the PDSCHs in the reference duration include a PDSCH that partially but not fully overlaps with the sub-band among the multiple sub-bands and a PDSCH that fully overlaps with the sub-band among the multiple sub-bands.