Groupcast HARQ Feedback Mediation for Hidden V2X Failures
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Solution Overview
Problem
In vehicle-to-everything (V2X) communication, groupcast transmissions may fail due to varying radio conditions among group members, leading to unsuccessful data reception and hidden failures in Hybrid Automatic Repeat Request (HARQ) feedback, especially when using NACK-only feedback options, as poor radio conditions can prevent transmitter UEs from receiving feedback from receiver UEs.
Innovation Solution
Wireless devices in the groupcast can request peer devices to modify HARQ feedback, such as reversing ACK to NACK or generating additional feedback, to ensure the transmitter receives feedback even in poor conditions, using mechanisms like SidelinkFakeHARQRequest and SidelinkFakeHARQResponse messages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If NACK-only HARQ feedback is used in groupcast, then feedback overhead is reduced, but reliability of feedback reception deteriorates due to hidden failures in poor radio conditions
Solution Approach 1:
The patent introduces a mediator mechanism where a successfully receiving UE acts as an intermediary to forward HARQ feedback information for UEs experiencing poor radio conditions. This mediator UE receives the original groupcast, determines that peer UEs have poor channel conditions, and then transmits modified HARQ feedback (such as fake NACK messages) to the transmitter UE on behalf of those peer UEs, ensuring the transmitter receives feedback information even when direct feedback from poor-condition UEs is lost
Solution Approach 2:
The patent implements preliminary action by having the mediator UE proactively identify UEs with poor radio conditions before feedback transmission fails. The mediator UE monitors channel conditions of peer UEs in advance, and when poor conditions are detected, pre-prepares and transmits modified HARQ feedback messages to the transmitter UE, preventing the hidden failure scenario from occurring
2Reliability
If peer UEs transmit modified HARQ feedback on behalf of UEs with poor radio conditions, then reliability of feedback reception is improved, but device complexity increases due to additional coordination mechanisms
Solution Approach 1:
The patent applies local quality by enabling only specific UEs that are in good radio conditions and have successfully received the groupcast to act as mediators, while other UEs with poor conditions simply receive normally. This selective activation of the mediator function based on local channel quality conditions avoids requiring all UEs to implement complex coordination logic, thereby reducing overall system complexity while maintaining reliability
3Loss of information
If HARQ feedback is transmitted from all group members, then completeness of feedback information is improved, but loss of time increases due to additional transmission processing
Solution Approach 1:
The patent implements partial action by having only the necessary number of mediator UEs transmit modified HARQ feedback messages, rather than requiring all group members to transmit. The system determines the minimum sufficient set of mediators needed to cover all peer UEs with poor conditions, thereby achieving complete feedback information coverage while minimizing the number of transmissions and reducing time loss
Data Source
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AI summary
There is provided receiving, by a receiver wireless device, a groupcast, from a transmitter wireless device of the groupcast, determining by the receiver wireless device, at least one trigger for requesting to modify Hybrid Automatic Repeat Request, HARQ, feedback, transmitting, by the receiver wireless device to one or more peer receiver wireless devices of the groupcast, based on the determined at least one trigger, at least one request to modify the HARQ feedback to the groupcast.