NR V2X Sidelink RLF Detection Under HARQ Feedback Drops
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Solution Overview
Problem
In sidelink (SL) communication, the issue of unnecessary radio link failure (RLF) declaration occurs due to half-duplex problems or transmission priority drops, leading to increased SL HARQ DTX generation counts despite good link quality between transmitting and receiving UEs.
Innovation Solution
A method for UEs to determine SL RLF by considering both SL HARQ DTX counts and out-of-sync (OOS) or in-sync (IS) conditions, thereby reducing false RLF declarations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If SL RLF is determined based only on SL HARQ DTX count, then the detection mechanism is simple, but false RLF declarations occur due to half-duplex problems or transmission priority drops
Solution Approach 1:
The patent introduces a feedback mechanism where the receiving UE sends PSFCH transmission status information to the transmitting UE. This feedback allows the transmitting UE to distinguish between actual link failures and situations where the receiving UE prioritized other transmissions, thereby reducing false RLF declarations while maintaining reasonable detection complexity
Solution Approach 2:
The patent uses PSFCH transmission status information as an intermediary element between the transmitting and receiving UEs. This intermediary provides additional context about the receiving UE's transmission state, enabling more accurate RLF determination without significantly increasing system complexity
2Measurement precision
If the TX UE monitors SL HARQ feedback continuously, then link quality is accurately monitored, but unnecessary RLF declarations occur due to half-duplex problems
Solution Approach 1:
The receiving UE provides feedback about its PSFCH transmission status, allowing the transmitting UE to understand when HARQ feedback absence is due to the receiving UE's transmission priorities rather than actual link degradation. This resolves the contradiction by maintaining monitoring while adding contextual understanding
Solution Approach 2:
The patent dynamically adjusts RLF determination based on the receiving UE's transmission state. When the receiving UE indicates it prioritized other transmissions, the transmitting UE temporarily suspends RLF declaration even if HARQ feedback is missing, making the detection system adaptive rather than static
3Reliability
If the RX UE prioritizes UL transmission over SL HARQ feedback, then UL communication reliability is improved, but SL RLF detection becomes inaccurate
Solution Approach 1:
The receiving UE performs preliminary action by notifying the transmitting UE of its intended PSFCH transmission status before actual transmission. This allows the transmitting UE to anticipate and correctly interpret the absence of HARQ feedback, preventing false RLF declarations while allowing UL priority transmission
Solution Approach 2:
The receiving UE provides feedback about its PSFCH transmission decisions, creating awareness at the transmitting UE end. This feedback mechanism allows the system to tolerate temporary HARQ feedback loss due to UL prioritization without triggering false RLF declarations
Data Source
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AI summary
Provided are a method for a first device carrying out wireless communication, and an apparatus supporting same. The method may comprise the steps of: transmitting sidelink control information (SCI) to a second device via a physical sidelink control channel (PSCCH); transmitting data to the second device via a physical sidelink shared channel (PSSCH) which is associated with the PSCCH; determining a physical sidelink feedback channel (PSFCH) resource on the basis of a slot and subchannel associated with the PSSCH; increasing a DTX counter by one on the basis of failing to receive hybrid automatic repeat request (HARQ) feedback on the PSFCH resource; receiving, from the second device, information related to dropping the transmission of the HARQ feedback; and decreasing the DTX counter by N on the basis of the information related to dropping the transmission of the HARQ feedback. Sidelink (SL) radio link failure (RLF) may be declared on the basis that the DTX counter reaches the maximum number of DTXs, and N may be a positive integer.