V2X Sidelink HARQ Process Adjustment for Buffer Overflow
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Solution Overview
Problem
In sidelink communication scenarios, especially in out-of-coverage scenarios, the transmitter UE lacks knowledge about the number of HARQ processes available at the receiver UE, 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 on the sidelink to indicate to the transmitter UE if a transmission is successfully identified but not buffered at the receiver UE, allowing adaptive retransmission strategies and buffer management, such as ACK, NACK, and LOST states, and dynamic negotiation or adjustment of HARQ processes based on buffer occupation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the transmitter UE continuously attempts retransmissions without knowing the receiver UE's buffer status, then transmission coverage is extended, but transmission reliability deteriorates due to unnecessary retransmissions when buffer is full
Solution Approach 1:
The patent implements feedback mechanisms where the receiver UE signals the transmitter UE about buffer status through HARQ feedback. This allows the transmitter to adapt its retransmission behavior based on actual buffer availability, preventing unnecessary retransmissions when the buffer is full while maintaining coverage where needed.
Solution Approach 2:
The system dynamically adjusts the number of active HARQ processes and retransmission strategies based on real-time buffer occupation status. The transmitter and receiver can negotiate and modify their HARQ process management dynamically to match actual buffer capacity and transmission conditions.
2Reliability
If the number of HARQ processes is increased to improve transmission reliability, then buffer requirements increase, leading to potential buffer overflow in out-of-coverage scenarios
Solution Approach 1:
The patent enables dynamic negotiation and adjustment of the number of active HARQ processes between transmitter and receiver UEs. The system can adapt the HARQ process count based on actual buffer capacity and transmission needs, preventing buffer overflow while maintaining adequate reliability.
Solution Approach 2:
The system changes operational parameters including the number of active HARQ processes and buffer allocation strategies based on detected buffer occupation levels. This allows optimization of reliability without excessive buffer consumption, particularly important for out-of-coverage scenarios with limited resources.
3Reliability
If feedback mechanisms are implemented to indicate buffer status, then transmission reliability improves, but device complexity increases due to additional signaling and negotiation protocols
Solution Approach 1:
The patent leverages existing HARQ feedback mechanisms to serve multiple purposes: indicating both decoding status and buffer availability. By making the feedback system multi-functional, the patent avoids adding separate dedicated signaling mechanisms, thus improving reliability without proportionally increasing device complexity.
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.