SL-U HARQ Acknowledgment Time Compensation for LBT Delays

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Solution Overview

Problem

Sidelink (SL) transmission on an unlicensed spectrum (SL-U) faces delays due to Listen Before Talk (LBT) failures, leading to resource wastage as Hybrid Automatic Repeat Request (HARQ) acknowledgments may be delayed, causing the network to incorrectly assume SL transmissions have failed and reassign resources unnecessarily.

Innovation Solution

Implementing a method where terminal devices receive transmission resources for SL-U, perform the transmission, obtain HARQ acknowledgments, and transmit them on resources configured to compensate for LBT delays, using pre-allocated, requested, or alternative resources such as PUCCH or PUSCH, ensuring timely acknowledgment delivery.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If Listen Before Talk (LBT) operation is performed prior to SL-U transmission, then channel access reliability is improved, but transmission delay increases causing HARQ acknowledgment to miss PUCCH resources

Engineering Contradiction:

Improvechannel access reliabilityVSAvoidtransmission delay

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The network device pre-allocates multiple PUCCH resources for HARQ acknowledgments before the actual SL-U transmission occurs. This preliminary resource preparation ensures that even if LBT delays occur, the UE has available resources to transmit acknowledgments without missing the deadline, thus resolving the contradiction between performing LBT for reliability and avoiding delay-induced resource loss.

Inventive Principle:

Principle #10Preliminary action

2Adaptability or versatility

If HARQ acknowledgment is delayed due to LBT failures, then resource allocation flexibility is maintained, but resource wastage occurs due to incorrect transmission failure assumptions

Engineering Contradiction:

Improveresource allocation flexibilityVSAvoidresource wastage

Core Design Contradiction:

Adaptability or versatilityVSLoss of substance

Solution Approach 1:

The system dynamically adjusts the HARQ acknowledgment timing by allowing the UE to select from multiple pre-configured PUCCH resources based on actual LBT outcomes. This dynamic adaptation enables the system to maintain resource allocation flexibility while preventing resource wastage, as the UE can transmit acknowledgments on alternative resources that are still within the valid time window, preventing the network from incorrectly assuming transmission failure and reassigning resources unnecessarily.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS20240430040A1Terminal Devices, Network Devices, and Methods Thereof

Publication Date: 2024.12.26 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

The present disclosure provides a method for Side Link (SL) transmission on an Unlicensed band (SL-U), performed by a first terminal device. The method includes: receiving transmission resources for the SL-U transmission allocated by a network device to the first terminal device; performing the SL-U transmission on the transmission resources to a second terminal device; obtaining a Hybrid Automatic Repeat Request, HARQ, acknowledgment associated with the SL-U transmission; configuring a resource for the HARQ acknowledgment; and transmitting the HARQ acknowledgement to the network device on the configured resource, wherein the configured resource is time compensated for Listen Before Talk (LBT) delays occurring during the SL-U transmission and/or during a transmission of the HARQ acknowledgement.