V2X Groupcast HARQ Feedback Resource Allocation
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Solution Overview
Problem
In V2X communication systems, the access stratum (AS) of a terminal cannot determine whether all members in a group successfully receive groupcast information, hindering the normal execution of the hybrid automatic repeat request (HARQ) mechanism for groupcast.
Innovation Solution
The V2X layer of a terminal sends a message with a group identifier to trigger response messages from other members, allowing the V2X layer to determine the quantity of reachable members and communicate this information to the AS, enabling the AS to assess successful receipt of groupcast information based on acknowledgement messages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the AS of a terminal executes the HARQ mechanism for groupcast without determining the quantity of reachable members, then the execution process is simple, but the HARQ mechanism cannot be normally executed due to inability to determine whether all members successfully received the groupcast information
Solution Approach 1:
The V2X layer performs preliminary actions by sending a first message to discover reachable members and determining the quantity of reachable members before the AS layer executes the HARQ mechanism. This preliminary member discovery enables the AS layer to properly execute HARQ by knowing how many members to expect ACKs from, without adding complex real-time determination logic during HARQ execution.
2Measurement precision
If the V2X layer determines the quantity of reachable members by receiving response messages from all members, then the member quantity is accurately determined, but the signaling overhead increases due to multiple response messages
Solution Approach 1:
The solution uses partial action by having only the necessary response messages sent for member discovery, rather than requiring all possible members to respond. The V2X layer determines the quantity of reachable members by processing received response messages, without requiring every member in the group to participate in the discovery process, thus reducing signaling overhead while maintaining accurate determination.
3Reliability
If the AS layer determines whether all members successfully received groupcast information without knowing the specific quantity of members, then the determination process is simplified, but the HARQ mechanism cannot function properly due to lack of member quantity information
Solution Approach 1:
The V2X layer acts as an intermediary between the physical layer (where ACK messages are received) and the AS layer (which needs member quantity information). The V2X layer determines the quantity of reachable members and provides this information to the AS layer, enabling the AS layer to properly execute HARQ by comparing the quantity of received ACKs with the determined quantity of reachable members, without the AS layer needing to directly track individual member responses.
Data Source
AI summary
A communication apparatus and method the method including receiving, by an access stratum (AS) of a terminal, a groupcast message, where the terminal corresponds to a member in a group, determining, by the AS of the terminal, a feedback resource based on a sequence number of the member, and sending, by the AS of the terminal, an acknowledgement (ACK)/negative acknowledgement (NACK) message of the groupcast message based on the feedback resource.