NR-U Contention Window Adjustment via CBG Counting
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Solution Overview
Problem
The challenge in wireless communication systems is to efficiently manage contention window sizes (CWS) in New Radio (NR) unlicensed spectrum to ensure fair coexistence with other technologies, particularly in the 5 GHz band, where listen before talk (LBT) procedures are required, and to adapt to varying data transmission sizes, such as large transport block sizes (TBS), while minimizing overhead and maintaining spectral efficiency.
Innovation Solution
The method involves determining and adjusting the contention window size (CWS) based on a reference burst set independent of subcarrier spacing, counting code block groups (CBGs) and negative acknowledgments (NACKs), and scheduling retransmissions accordingly, using configurable CBG-based transmission procedures to optimize CWS adjustments for both uplink and downlink communications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the contention window size is adjusted based on subcarrier spacing-dependent reference bursts, then the CWS adjustment can be optimized for specific numerologies, but the system complexity increases and adaptability across different numerologies deteriorates
Solution Approach 1:
The reference burst is segmented into code block groups (CBGs) for independent counting and evaluation. Each CBG can be individually assessed for NACK conditions, allowing precise CWS adjustment based on actual transmission failures rather than subcarrier spacing characteristics. This segmentation enables numerology-independent operation while maintaining accurate measurement of transmission reliability.
Solution Approach 2:
The patent changes the fundamental parameter for CWS adjustment from subcarrier spacing-dependent time resources to CBG-based counting that is independent of subcarrier spacing. By using a fixed number of CBGs (e.g., 4 CBGs per reference burst) regardless of numerology, the system achieves parameter independence while maintaining accurate CWS adaptation through CBG-level failure detection.
2Productivity
If CBG-based transmission is used to reduce retransmission overhead, then spectral efficiency improves, but the complexity of managing CBG-level acknowledgments and retransmissions increases
Solution Approach 1:
The patent extracts the acknowledgment and retransmission management from the traditional transport block level down to the code block group level. By taking out individual CBGs as independent units for NACK detection and retransmission scheduling, the system achieves finer-grained control that reduces overall retransmission overhead while managing complexity through standardized CBG handling procedures.
Solution Approach 2:
The system dynamically adjusts the number of CBGs per reference burst based on transmission conditions and numerology configurations. This dynamic adaptation allows the system to optimize between overhead reduction and complexity management by flexibly configuring CBG granularity according to channel conditions, traffic patterns, and numerology selections.
3Reliability
If the reference burst spans the entire UL/DL burst, then all transmissions are captured for CWS adjustment, but the measurement time increases and responsiveness to recent transmission conditions decreases
Solution Approach 1:
Instead of using the entire UL/DL burst as the reference burst, the patent applies partial action by selecting only a portion of the burst (e.g., a specific number of slots or a fixed time duration) for CWS measurement. This partial reference burst approach provides timely CWS adjustment based on recent transmission conditions while avoiding the latency of processing the entire burst, achieving a balance between reliability and responsiveness.
Data Source
AI summary
Some embodiments of this disclosure include systems, apparatuses, methods, and computer-readable media for use in a wireless network for facilitating retransmission procedures in New Radio (NR) technologies. Some embodiments are directed to a method that includes determining a contention window size (CWS) of an uplink/downlink (UL/DL) communication channel in a new radio unlicensed (NR-U) spectrum. The method also includes adjusting the CWS based on: defining a reference UL/DL burst set at a predetermined time length independent from a subcarrier spacing and partially spanning an UL/DL burst, and counting one or more code block groups (CBGs) in the reference UL/DL burst. The method further includes scheduling a retransmission of an UL/DL communication in the NR-U spectrum based on the adjusted CWS.