Sidelink Feedback Timing in DRX With Multiple PSFCH Occasions
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Solution Overview
Problem
In wireless communication systems, the inconsistency in initiating the round-trip-time (RTT) timer and retransmission timer during discontinuous reception (DRX) mode due to multiple physical sidelink feedback channel (PSFCH) occasions leads to confusion regarding when these timers should be started, particularly in advanced networks with multiple PSFCH occasions.
Innovation Solution
A user equipment (UE) selects a PSFCH occasion from a set of allocated occasions to initiate the RTT timer, which can be after the same, first, or last PSFCH occasion, or based on listen-before-talk (LBT) procedures, and upon expiration, initiates a retransmission timer to monitor for a retransmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple PSFCH occasions are allocated for feedback transmission, then feedback reliability is improved, but timer initiation confusion increases
Solution Approach 1:
The patent introduces a selection mechanism that acts as an intermediary between multiple PSFCH occasions and timer initiation. The UE selects one specific PSFCH occasion from the multiple allocated occasions based on predefined criteria (e.g., first occasion, last occasion, or occasion with best channel conditions), and this selected occasion becomes the reference point for RTT and retransmission timer initiation. This intermediary selection process resolves the confusion by providing a clear, unambiguous trigger point while maintaining the benefits of multiple feedback opportunities.
Solution Approach 2:
The patent applies preliminary action by having the UE pre-determine which PSFCH occasion will be used for timer initiation before actual feedback transmission. The selection of the reference PSFCH occasion is made in advance based on configuration or channel conditions, so that when feedback transmission occurs, the timer initiation point is already clearly defined. This eliminates real-time decision-making complexity and ensures consistent timer management.
2Loss of time
If RTT timer is initiated after each PSFCH occasion, then feedback response time is reduced, but energy consumption increases
Solution Approach 1:
The patent extracts the timer initiation action from all PSFCH occasions and applies it only to the selected reference PSFCH occasion. Instead of initiating RTT timers after every feedback opportunity, the system identifies one specific occasion (e.g., the first successful feedback transmission or a pre-configured occasion) and initiates timers only after that selected occasion. This extraction reduces unnecessary timer operations and associated energy consumption while maintaining appropriate response timing.
3Productivity
If multiple feedback channel occasions are provided, then DRX efficiency is improved, but monitoring complexity increases
Solution Approach 1:
The patent introduces a clear mapping relationship as an intermediary between multiple PSFCH occasions and the single retransmission monitoring point. The selected PSFCH occasion serves as the reference that determines when the retransmission monitoring window should open. This intermediary mapping simplifies monitoring by providing a deterministic rule: monitor for retransmission starting from a specific time offset after the selected PSFCH occasion, regardless of how many other feedback occasions exist.
Data Source
AI summary
Methods, systems, and devices for wireless communication are described. A user equipment (UE) may receive, while operating in a discontinuous reception mode, a grant scheduling a sidelink data message for the UE over a shared radio frequency spectrum band, the grant indicating a set of feedback channel occasions associated with the sidelink data message. The UE may transmit at least one feedback message indicating a feedback status of the sidelink data message during at least one feedback channel occasion of the set of feedback channel occasions. The UE may initiate, based at least in part on the at least one feedback channel occasion, a round-trip timer associated with the at least one feedback message during which the UE suppresses monitoring for a retransmission of the sidelink data message.