NR Sidelink Contention Window Adjustment in FR-1 Unlicensed Bands
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Solution Overview
Problem
The existing sidelink (SL) communication systems in unlicensed bands face challenges in adapting contention window sizes (CWS) dynamically due to the absence of HARQ feedback from a gNB and the need to comply with regulatory requirements for LBT measurements across varying bandwidths, which affects channel access efficiency and fairness in multi-user scenarios.
Innovation Solution
The proposed solution involves adjusting the CWS based on HARQ-ACK feedback from other UEs for unicast transmissions and maintaining or increasing the CWS for broadcast transmissions, while also defining energy detection thresholds and LBT measurement bandwidths to ensure regulatory compliance and efficient channel access, allowing for flexible operation in sub-channels and supporting multi-carrier operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the contention window size is adjusted dynamically based on HARQ feedback, then channel access efficiency is improved, but the system complexity increases due to the absence of gNB HARQ feedback in sidelink communication
Solution Approach 1:
The UE performs autonomous CWS adjustment by monitoring HARQ-ACK feedback from other UEs and determining channel access parameters independently, without requiring gNB control. The UE serves itself by implementing LBT procedures and contention window adaptation based on local observations of channel conditions and received feedback.
Solution Approach 2:
The system utilizes HARQ-ACK feedback from receiving UEs to adjust the transmitting UE's contention window size. The feedback mechanism enables adaptive CWS adjustment where the UE modifies its channel access parameters based on the success or failure of previous transmissions as indicated by received HARQ-ACK signals.
2Adaptability or versatility
If LBT measurements are performed across varying bandwidths to comply with regulatory requirements, then regulatory compliance is achieved, but channel access fairness deteriorates in multi-user scenarios
Solution Approach 1:
The UE performs LBT measurements on specific sub-channels where it intends to transmit, rather than across the entire bandwidth. The energy detection threshold is applied locally to the relevant sub-channel, allowing compliance with regulatory requirements while maintaining fairness by limiting the measurement scope to the actual transmission resources.
Solution Approach 2:
The bandwidth is divided into multiple sub-channels, and LBT measurements are performed independently on each sub-channel. This segmentation allows the system to comply with regulatory requirements for bandwidth-specific measurements while preventing users from gaining unfair advantage by measuring across the entire bandwidth.
3Stability of the object's composition
If the contention window size is maintained or increased for broadcast transmissions, then channel access stability is improved, but channel access efficiency decreases
Solution Approach 1:
The CWS adjustment mechanism adapts dynamically based on transmission type. For unicast transmissions, CWS is adjusted based on HARQ-ACK feedback to optimize efficiency. For broadcast transmissions, CWS is maintained or increased to ensure stability and prevent collisions, with the specific adjustment depending on the observed channel conditions and feedback from receiving UEs.
Data Source
AI summary
Various embodiments herein provide techniques related to adjustment of contention window size for new radio (NR) sidelink (SL) systems. Specifically, embodiments may relate to NR SL systems operating in the frequency range 1 (FR-1) unlicensed band, and using type 1 listen-before-talk (LBT). Embodiments further relate to LBT bandwidth (BW) definitions in such systems. Other embodiments may be described and/or claimed.