PSFCH HARQ Feedback LBT Failure Handling
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Solution Overview
Problem
Existing 5G NR sidelink communication systems face inefficiencies in unlicensed spectrum due to the inability of receiving UEs to send ACK/NACK feedback without successful LBT, leading to reduced throughput and unreliable HARQ feedback in unlicensed bands.
Innovation Solution
The method involves configuring multiple PSFCH resources for HARQ feedback, allowing the UE to perform LBT on the first resource and, if unsuccessful, attempt LBT on subsequent resources, and utilizing short control exemptions or COT sharing to transmit HARQ feedback without additional LBT sensing, thereby increasing the chances of successful channel access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the receiving UE performs LBT sensing before transmitting HARQ feedback on the assigned PSFCH resource, then the transmission follows the standard unlicensed band access procedure, but the LBT may fail and prevent the HARQ feedback from being sent
Solution Approach 1:
The single PSFCH resource is segmented into multiple alternative resources (first PSFCH resource and second PSFCH resource). The UE attempts to transmit on the first resource after LBT, and if that fails, switches to the second resource. This segmentation provides redundancy and increases the probability of successful feedback transmission.
Solution Approach 2:
The system prepares multiple PSFCH resources in advance as a cushion against LBT failure. Instead of having no backup plan, the UE is pre-configured with alternative transmission resources, ensuring that HARQ feedback can still be sent even if the primary transmission opportunity is lost.
2Speed
If the UE is allowed to transmit HARQ feedback without performing LBT sensing on the second PSFCH resource, then the transmission speed increases and feedback is sent faster, but this may violate unlicensed band regulations requiring LBT
Solution Approach 1:
The network configuration acts as an intermediary that grants permission for LBT-exempt transmission. The gNB configures the second PSFCH resource and implicitly or explicitly allows the UE to transmit on it without LBT, mediating between the need for fast feedback and regulatory requirements.
Solution Approach 2:
The system changes the LBT parameter (from performing LBT to not performing LBT) for the second PSFCH resource compared to the first resource. This parameter change enables faster transmission on the backup resource while maintaining regulatory compliance through the initial LBT on the primary resource.
3Reliability
If multiple PSFCH resources are configured for HARQ feedback, then the probability of successful LBT increases and feedback reliability improves, but the system complexity and resource overhead increase
Solution Approach 1:
The feedback resource is segmented into multiple options, with the first being the primary choice and the second being the backup. This segmentation is simple and straightforward, requiring the UE to only know when to switch resources (after LBT failure) rather than managing complex resource selection algorithms.
Solution Approach 2:
Instead of configuring a large number of PSFCH resources, the system uses exactly two resources - just enough to provide redundancy without excessive overhead. This partial action approach achieves the necessary reliability improvement without proportionally increasing system complexity.
Data Source
AI summary
According to an embodiment of the present disclosure, a system and a method may include receiving, by a first user equipment (UE), configuration information for physical sidelink feedback channel (PSFCH) resources; performing, by the first UE in response to the receiving, a first listen-before-talk (LBT) sensing for a first PSFCH resource of the PSFCH resources; and determining that the first LBT sensing failed and in response, transmitting a signal over a second PSFCH resource of the PSFCH resources.