Radio Link Monitoring Backup Resources for 5G Reliability
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Solution Overview
Problem
Current 5G NR systems face challenges in accurately monitoring radio link quality, leading to unnecessary Radio Link Failures (RLFs) due to failures in transmitting Radio Link Monitoring (RLM) reference signals, especially when operating on unlicensed spectrum, which can disrupt ongoing services and trigger unnecessary re-establishment procedures.
Innovation Solution
The method involves a user equipment (UE) that receives an RLM configuration, monitors both primary and backup RLM reference signal resources to determine radio link quality, and sends indications to higher layers based on these qualities, using specific thresholds and timers to differentiate between in-sync and out-of-sync conditions, thereby avoiding unnecessary RLF declarations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE monitors only the primary RLM-RS resource, then the device complexity is reduced, but the reliability of radio link monitoring deteriorates due to false RLF declarations when primary resources fail
Solution Approach 1:
The network configures backup RLM-RS resources in advance before primary resources fail. When the UE detects that primary RLM-RS resources have failed (through out-of-sync indications), it switches to monitoring the pre-configured backup resources, avoiding service interruption and false RLF declarations.
Solution Approach 2:
Backup RLM-RS resources are prepared beforehand as a cushion against primary resource failures. This cushioning mechanism ensures that when primary resources fail due to transmission issues or blockages, the UE immediately has alternative resources to monitor, maintaining reliable radio link assessment without triggering unnecessary re-establishment procedures.
2Reliability
If the UE switches to backup RLM-RS resources when primary quality deteriorates, then the reliability of radio link monitoring is improved, but the device complexity increases due to multiple resource monitoring
Solution Approach 1:
The RLM-RS monitoring mechanism is made dynamic by allowing the UE to switch between primary and backup resources based on detected link conditions. The UE monitors primary resources normally, and only activates backup resource monitoring when out-of-sync indications are received, creating an adaptive monitoring system that adjusts to actual radio conditions.
Solution Approach 2:
The UE autonomously determines when to switch from primary to backup RLM-RS resources based on its own measurements of downlink radio link quality. When the UE detects that primary resource quality has deteriorated below a threshold, it automatically initiates monitoring of backup resources without network intervention, enabling self-service operation.
3Measurement precision
If the UE uses multiple RLM-RS resources for monitoring, then the measurement precision of radio link quality is improved, but the loss of time increases due to additional monitoring operations
Solution Approach 1:
The UE performs partial monitoring by focusing primarily on primary RLM-RS resources under normal conditions, and only activates excessive action (monitoring backup resources) when absolutely necessary. This partial/excessive approach balances measurement precision with time efficiency, achieving accurate link assessment without continuous dual-resource monitoring overhead.
Solution Approach 2:
The monitoring of backup RLM-RS resources is performed periodically or event-triggered rather than continuously. The UE monitors primary resources continuously, and switches to backup resource monitoring periodically or when specific conditions (out-of-sync indications) are met, reducing overall time consumption while maintaining measurement precision when needed.
Data Source
AI summary
A method for radio link monitoring (RLM) performed by a user equipment (UE) is provided. The method includes: receiving, from a serving cell, an RLM configuration; monitoring an RLM reference signal (RS) (RLM-RS) resource indicated by the RLM configuration to determine a first downlink (DL) radio link quality; monitoring a backup RLM-RS resource that is associated with the RLM-RS resource to determine a second DL radio link quality after determining that the first DL radio link quality is lower than a threshold and the RLM configuration also indicates the backup RLM-RS resource; and sending, via a physical (PHY) layer of the UE, an RLM indication to a higher layer of the UE based on at least one of the first DL radio link quality and the second DL radio link quality.