Sidelink DRX Fallback for Legacy gNB Groupcast Communication

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Solution Overview

Problem

Legacy network nodes, such as gNB in 3GPP Release16, do not support sidelink (SL) discontinuous reception (DRX) configuration, leading to unclear UE behavior in such networks.

Innovation Solution

A method for a terminal device to determine if an access network node is incapable of SL DRX, using preconfigured SL DRX configuration for groupcast/broadcast communication, and informing peer devices or switching to autonomous resource allocation modes when SL DRX is not supported.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If a legacy gNB (not supporting SL DRX) provides network coverage, then UEs can access the network, but SL DRX functionality cannot be provided and UEs cannot achieve power-saving benefits

Engineering Contradiction:

ImproveUE power consumptionVSAvoidSL DRX configuration availability

Core Design Contradiction:

Use of energy by moving objectVSAdaptability or versatility

Solution Approach 1:

The patent applies preliminary action by pre-configuring SL DRX parameters in the UE before the UE encounters a legacy gNB. The UE stores default SL DRX configuration values in advance, which can be immediately applied when connecting to legacy gNBs that cannot provide SL DRX configuration, thereby maintaining power-saving functionality without requiring real-time configuration from the network.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements self-service by enabling the UE to autonomously determine whether the current gNB supports SL DRX and to self-configure SL DRX parameters without network assistance. The UE monitors for SL DRX configuration messages from the gNB, and upon determining the gNB is legacy (does not support SL DRX), the UE automatically applies pre-stored default configurations and adjusts its monitoring behavior accordingly.

Inventive Principle:

Principle #25Self-service

2Reliability

If the UE monitors for SL DRX configuration from the network, then the UE can obtain proper configuration, but the UE cannot operate properly when the network node does not support SL DRX

Engineering Contradiction:

ImproveSL DRX operation reliabilityVSAvoidUE behavior clarity

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent applies feedback by implementing a monitoring mechanism where the UE actively checks for SL DRX configuration messages from the gNB. Based on the presence or absence of these configuration messages, the UE feedback-adjusts its behavior: when configuration is received, the UE applies it; when no configuration is received (indicating a legacy gNB), the UE switches to using pre-configured default values, ensuring reliable operation in both scenarios.

Inventive Principle:

Principle #23Feedback

3Reliability

If the UE camps on a legacy gNB for network access, then the UE can maintain connectivity, but the UE loses power-saving benefits from SL DRX

Engineering Contradiction:

Improvenetwork connectivityVSAvoidUE power consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent implements self-service by enabling the UE to autonomously detect that it is connected to a legacy gNB (through monitoring for SL DRX configuration messages) and to automatically apply pre-stored default SL DRX configurations. This self-service mechanism ensures the UE maintains connectivity while minimizing power consumption through autonomous configuration application, without requiring network assistance.

Inventive Principle:

Principle #25Self-service

4Use of energy by moving object

If the network provides SL DRX configuration, then the UE can achieve power-saving benefits, but the network must support SL DRX functionality

Engineering Contradiction:

ImproveUE power consumptionVSAvoidnetwork compatibility

Core Design Contradiction:

Use of energy by moving objectVSAdaptability or versatility

Solution Approach 1:

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements universality by designing a dual-mode SL DRX configuration mechanism that works with both legacy gNBs and modern gNBs supporting SL DRX. The UE can operate in network-configured mode when connected to modern gNBs and in autonomous pre-configured mode when connected to legacy gNBs, making the power-saving functionality universal across different network types.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS12610428B2Method and apparatus for sidelink discontinuous reception

Publication Date: 2026.04.21 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

Embodiments of the present disclosure provide method and apparatus for SL DRX. A method performed by a terminal device comprises receiving system information block (SIB). The method further comprises determining whether an access network node is incapable of sidelink, SL, discontinuous reception (DRX). The method further comprises, when sidelink, SL, discontinuous reception, DRX, configuration used for groupcast/broadcast and/or configuration of a SL frequency is absent in the SIB, using preconfigured SL DRX configuration for groupcast/broadcast communication of the terminal device. The method further comprises, when a serving access network node of the terminal device is SL DRX incapable, informing a peer terminal device that the terminal device cannot adopt SL DRX for its transmission and/or forbidding transmitting groupcast/broadcast service when SL DRX is required to be configured.