NR-U CWS Adjustment via HARQ Feedback Timer
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Solution Overview
Problem
The challenge in adapting New Radio (NR) systems for unlicensed spectrum access is maintaining fair coexistence with incumbent technologies, particularly due to the assumption in legacy systems that HARQ-ACK feedback would always be received on licensed carriers, which is not the case in standalone NR-U operations subject to Listen-Before-Talk (LBT) procedures.
Innovation Solution
The proposed solution involves modifying the contention window size (CWS) adjustment mechanism by introducing a timer-based approach that adjusts CWS based on Hybrid Automatic Repeat Request (HARQ) feedback, allowing for flexible timing of CWS updates and ensuring fair coexistence with other technologies operating in unlicensed spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If NR systems operate in standalone mode on unlicensed carriers with LBT procedures, then spectrum availability is improved, but HARQ feedback reception reliability deteriorates due to potential feedback loss on unlicensed carriers
Solution Approach 1:
The patent introduces a timer as an intermediary mechanism to bridge the gap between HARQ feedback transmission and CWS adjustment. The timer provides a controlled waiting period that accounts for the unreliable feedback channel, allowing the system to distinguish between feedback that is delayed due to LBT procedures versus feedback that is completely lost, thereby resolving the contradiction between utilizing unlicensed spectrum and maintaining feedback reliability.
Solution Approach 2:
The system performs preliminary actions by starting a timer before expecting HARQ feedback. This preliminary timing mechanism prepares the system in advance for the potential delays inherent in unlicensed spectrum operations, allowing it to proactively adjust CWS based on the elapsed time rather than reactively responding to feedback loss, thus maintaining reliability while operating on unlicensed carriers.
2Adaptability or versatility
If CWS adjustment is based on HARQ feedback timing, then coexistence fairness with incumbent technologies is improved, but system complexity increases due to timer management and feedback timing coordination
Solution Approach 1:
The patent changes the parameter basis for CWS adjustment from immediate HARQ feedback receipt to a time-based parameter (timer expiration). This parameter transformation simplifies the adjustment logic by using a single time threshold rather than complex feedback analysis, thereby improving coexistence fairness through consistent timing-based decisions while actually reducing system complexity compared to sophisticated feedback interpretation mechanisms.
3Reliability
If timer-based CWS adjustment is implemented, then HARQ feedback delay management is improved, but transmission latency increases due to waiting for timer expiration
Solution Approach 1:
The patent implements dynamic CWS adjustment where the timer duration can be configured and adapted based on system conditions, traffic patterns, and observed LBT behavior. This dynamic approach allows the system to optimize the balance between reliable feedback management and transmission latency, adjusting the waiting period as needed rather than using a fixed timeout, thereby resolving the contradiction between delay management and latency.
Data Source
AI summary
Systems, methods, and circuitries are provided for adjusting contention window size (CWS). An example method includes selecting a downlink (DL) burst transmitted by the gNB for use in determining the CWS and adjusting the CWS based on Hybrid Automatic Repeat Request (HARQ) feedback received with respect to the selected DL burst.