UE Validity Timer Handling for NTN Handover Synchronization
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Solution Overview
Problem
In wireless communication systems, particularly in Non-Terrestrial Networks (NTN), User Equipment (UE) faces challenges in handling validity timers during handover procedures, leading to incorrect assessment of assistance information validity, which can result in loss of uplink synchronization and subsequent communication disruptions.
Innovation Solution
The implementation of a method where the UE receives system information including NTN configurations for both serving and target cells, manages validity timers accordingly by starting or restarting them based on received configurations, and handles RRC reconfiguration messages to maintain synchronization during handovers, preventing timer expiration and ensuring continuous communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE starts or restarts the validity timer based on the first NTN configuration for the serving cell, then the UE can maintain uplink synchronization for the serving cell, but the validity timer may incorrectly expire during handover to the target cell, causing the UE to incorrectly consider assistance information invalid
Solution Approach 1:
The UE performs preliminary action by stopping the validity timer upon receiving the RRC reconfiguration message with ReconfigurationWithSync for the target cell, before the handover is completed. This prevents the timer from expiring during the handover process and incorrectly invalidating the assistance information for the target cell. The timer is then restarted based on the second NTN configuration after handover completion, ensuring continuous and accurate validity assessment.
2Measurement precision
If the UE continues running the validity timer during handover procedure, then the timer expiration can be detected, but it leads to incorrect assessment of assistance information validity for the target cell when UL synchronization is actually valid
Solution Approach 1:
The validity timer handling is made dynamic by adapting its operation to the handover state. The timer is stopped when the UE receives the RRC reconfiguration message indicating handover to a target cell, and restarted after handover completion based on the new NTN configuration. This dynamic adjustment ensures the timer accurately reflects the validity period of assistance information for the current serving cell throughout the handover process, preventing incorrect expiration assessments.
3Reliability
If the UE stops the validity timer upon receiving RRC reconfiguration message with ReconfigurationWithSync, then incorrect timer expiration is prevented, but the timer needs to be restarted based on the second NTN configuration to maintain continuous validity monitoring
Solution Approach 1:
The UE implements feedback by monitoring the completion of the handover procedure and using this information to restart the validity timer with the new NTN configuration of the target cell. This feedback mechanism ensures the timer is synchronized with the actual serving cell state, maintaining continuous and accurate validity monitoring of assistance information without requiring complex manual intervention or additional signaling.
Data Source
AI summary
Methods, systems, and apparatuses can comprise a User Equipment (UE) receiving a system information including at least a first Non-terrestrial Network (NTN) configuration for a serving cell, starting or restarting a validity timer for the serving cell in response to receiving the system information, receiving a Radio Resource Control (RRC) reconfiguration message with ReconfigurationWithSync for a target cell, stopping, in response to receiving the RRC reconfiguration message, the validity timer that is running based on the first NTN configuration, and starting the validity timer based on a second NTN configuration for the target cell.