Sidelink HARQ Buffer Feedback for Reliable V2X Retransmissions
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Solution Overview
Problem
In sidelink communication scenarios, especially in out-of-coverage scenarios, the transmitter UE lacks knowledge about the receiver UE's available HARQ processes, leading to potential buffer overflow and reduced transmission reliability due to unnecessary retransmissions when a successfully identified transmission is not buffered.
Innovation Solution
Implement feedback mechanisms for sidelink communication, allowing the receiver UE to indicate if a transmission is successfully identified but not buffered, and adapt retransmission strategies based on buffer occupation or negotiate HARQ process numbers with the transmitter UE.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the transmitter UE performs retransmissions without knowing the receiver UE's buffer status, then transmission reliability may be improved through redundancy, but buffer overflow occurs and resources are wasted due to unnecessary retransmissions
Solution Approach 1:
The patent implements a feedback mechanism where the receiver UE sends buffer status reports to the transmitter UE. The feedback includes information about the current buffer occupation level, enabling the transmitter to make informed decisions about retransmissions. This resolves the contradiction by providing the transmitter with knowledge of the receiver's buffer status, preventing buffer overflow while maintaining transmission reliability through targeted retransmissions only when buffer capacity is available.
Solution Approach 2:
The patent introduces dynamic adaptation of retransmission strategies based on real-time buffer status. The transmitter UE adjusts its retransmission behavior dynamically according to the receiver's buffer occupation level reported in feedback messages. When buffer occupancy is high, retransmissions are suppressed or delayed; when buffer occupancy is low, retransmissions are permitted. This dynamic approach resolves the contradiction between maintaining reliability and preventing resource waste.
2Reliability
If the transmitter UE sends multiple retransmissions to ensure delivery, then transmission reliability improves, but transmission delay increases due to unnecessary retransmissions when buffer is full
Solution Approach 1:
The buffer status feedback mechanism enables the transmitter to immediately know when the receiver's buffer is full, allowing it to suppress unnecessary retransmissions. This prevents time loss from sending redundant data that cannot be buffered, while still maintaining reliability by sending retransmissions only when buffer space is confirmed available. The feedback loop creates an efficient timing mechanism that eliminates wasteful delays.
Solution Approach 2:
The patent employs preliminary action by having the receiver UE proactively report buffer status before the transmitter attempts retransmissions. The buffer status information is provided in advance, allowing the transmitter to plan retransmission timing optimally. This preliminary knowledge prevents both buffer overflow and unnecessary delays, as the transmitter can schedule retransmissions to coincide with periods when buffer capacity is available.
3Reliability
If the receiver UE buffers all transmissions for combining, then transmission reliability improves through soft combining, but device complexity increases due to buffer management overhead
Solution Approach 1:
The patent applies partial action by having the receiver buffer only those transmissions that are necessary for successful decoding. Instead of buffering all incoming transmissions indiscriminately, the receiver uses the buffer status feedback mechanism to determine when buffering is needed and when it can be avoided. This partial buffering approach maintains reliability through soft combining when necessary, while reducing buffer management complexity by avoiding unnecessary buffering operations.
Data Source
AI summary
A user device, UE, for a wireless communication system is described. The wireless communication system includes a plurality of user devices, UEs. The UE communicates with one or more transmitting UEs using a sidelink, supports a certain number of HARQ processes, and buffers one or more transmissions for each HARQ process. During a unicast communication with a transmitting UE using the sidelink, the UE receives from the transmitting UE a transmission during a transmission time interval, the transmission associated to control data, e.g. SCI, including a HARQ process ID, buffers the received transmission for the HARQ process, and combines the buffered transmissions prior to decoding. In case a successfully identified transmission is not buffered, the UE indicates to the transmitting UE that the transmission is not buffered at the UE.