Relay UE RRC Connection Failure Handling in Sidelink

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Solution Overview

Problem

In wireless communication systems, particularly in 5G networks, there is a challenge when a relay UE fails in RRC connection while attempting RRC connection based on RRCSetupRequest from a remote UE in sidelink.

Innovation Solution

The proposed solution involves an operation method for sidelink of a relay UE, which includes establishing a PC5 RRC connection with a remote UE, transmitting a message related to RRC connection to a base station, and receiving an RRCReject message. Based on this message, the relay UE informs the remote UE of the Uu RRC connection failure.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the relay UE attempts to establish RRC connection with the base station on behalf of the remote UE, then the remote UE can access the network through sidelink relay, but the RRC connection may fail due to base station rejection

Engineering Contradiction:

Improvesidelink relay capabilityVSAvoidRRC connection establishment

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The relay UE implements a feedback mechanism by monitoring RRCReject messages from the base station and notifying the remote UE of the connection failure. This feedback loop enables the remote UE to take corrective actions such as selecting a new relay UE or attempting direct connection, thereby resolving the reliability issue while maintaining sidelink relay functionality.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system performs preliminary error handling by establishing a failure notification mechanism before the remote UE is completely blocked. When RRC connection failure is detected, the relay UE proactively informs the remote UE, enabling the remote UE to prepare alternative connection strategies in advance, thus preventing complete communication breakdown.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If the relay UE notifies the remote UE of RRC connection failure, then the remote UE can search for new relay UE or perform reestablishment, but additional signaling messages are required

Engineering Contradiction:

Improveconnection failure handlingVSAvoidsignaling overhead

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The failure notification mechanism enables the remote UE to self-diagnose and self-correct connection issues. By receiving failure information from the relay UE, the remote UE autonomously decides whether to search for a new relay UE or attempt reestablishment, reducing the need for complex network-side intervention and minimizing overall signaling overhead.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The error handling functionality is extracted as a separate notification mechanism independent of the main RRC connection procedure. The relay UE extracts failure information from RRCReject messages and transmits it separately to the remote UE, allowing the main connection establishment process to remain simple while adding targeted error handling capability.

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentUS20250142645A1Operation method related to RRC connection and connection failure of a relay UE in a sidelink relay in a wireless communication system

Publication Date: 2025.05.01 LG ELECTRONICS INC

AI summary

An embodiment relates to an operation method related to sidelink of a relay user equipment (UE) in a wireless communication system, including establishing PC5 RRC connection with a remote UE by the relay UE, transmitting a message related to RRC connection to a base station (BS) by the relay UE, and receiving an RRCReject message from the BS by the relay UE, wherein, based on reception of the RRCReject message, the relay UE transmits a message informing Uu RRC connection failure to the remote UE.