Sidelink HARQ-ACK Feedback Handling When PSFCH Is Disabled

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

In sidelink communication of Release 16 NR, there is a need to clarify the operation of a transmitting terminal's feedback to a base station when the function for transmitting Hybrid Automatic Repeat Request-Acknowledgement (HARQ-ACK) from a receiving terminal via a Physical Sidelink Feedback Channel (PSFCH) is disabled.

Innovation Solution

The transmitting terminal selects a specific operation related to HARQ-ACK feedback to the base station, such as transmitting an ACK or not transmitting HARQ-ACK, based on various conditions including configuration, channel state, distance, and timing overlaps, to handle the disabled HARQ-ACK feedback from the receiving terminal.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If the function for transmitting HARQ-ACK from a receiving terminal via a PSFCH is disabled, then the device complexity is reduced and unnecessary transmissions are avoided, but the reliability of feedback operations becomes unclear

Engineering Contradiction:

Improvefeedback transmission functionVSAvoidfeedback operation reliability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The transmitting terminal autonomously determines whether to transmit HARQ-ACK feedback to the base station based on whether it received HARQ-ACK from the receiving terminal, without requiring complex configuration or control signaling from the base station. This self-service mechanism reduces device complexity while ensuring reliable feedback operations.

Inventive Principle:

Principle #25Self-service

2Reliability

If the transmitting terminal always transmits HARQ-ACK feedback to the base station, then the reliability of feedback is maintained, but the quantity of transmissions increases and communication efficiency decreases

Engineering Contradiction:

Improvefeedback reliabilityVSAvoidcommunication efficiency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The transmitting terminal uses the HARQ-ACK received from the receiving terminal as feedback to determine its own feedback transmission behavior to the base station. When HARQ-ACK is received, the transmitting terminal does not transmit feedback to the base station, reducing unnecessary transmissions and improving communication efficiency while maintaining reliability.

Inventive Principle:

Principle #23Feedback

3Reliability

If the transmitting terminal transmits HARQ-ACK feedback to the base station when HARQ-ACK is not received from the receiving terminal, then the reliability of feedback is ensured, but the quantity of transmissions increases unnecessarily

Engineering Contradiction:

Improvefeedback operation reliabilityVSAvoidtransmission quantity

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The transmitting terminal performs feedback transmission to the base station only when necessary (i.e., when HARQ-ACK is not received from the receiving terminal), rather than always transmitting or never transmitting. This partial action approach ensures reliability when needed while avoiding excessive transmissions that would increase the quantity of transmissions unnecessarily.

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS12557072B2Terminal and communication method

Publication Date: 2026.02.17 NTT DOCOMO INC

AI summary

A terminal includes a transmitting unit that transmits, on a sidelink resource, at least one of a transport block or control information; and a control unit that selects a specific operation related to feedback, to a base station, of Hybrid Automatic Repeat Request-Acknowledgement (HARQ-ACK) for the sidelink resource, in response to detecting that feedback for the at least one of the transport block or the control information is not performed.