NTN L1/L2 Mobility Handover With Timing Pre-Compensation
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Solution Overview
Problem
Existing mobile communication systems face challenges in efficiently managing mobility in non-terrestrial networks (NTNs) due to the dynamic nature of satellite-based communication, particularly in terms of timing advance (TA) acquisition and handover processes.
Innovation Solution
Implementing L1/L2 triggered mobility (LTM) support in wireless transmit/receive units (WTRUs) for NTNs, which includes receiving RRC configuration information for NTN candidate cells, performing beam-level measurements, and triggering events based on location-based timing pre-compensation and measurement conditions to facilitate seamless handovers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional mobility management methods are used in NTN, then handover processes can be completed, but timing advance acquisition becomes inefficient and communication links become unstable due to satellite dynamics
Solution Approach 1:
The patent applies preliminary action by performing TA acquisition before handover execution. The source gNB provides TA information to the WTRU in advance through RRC configuration or MAC CE signaling, allowing the WTRU to have TA value ready before switching to the target cell. This prevents communication link instability during handover and ensures continuous uplink synchronization in the NTN environment where propagation delays change dynamically.
Solution Approach 2:
The patent uses the source gNB as an intermediary to transfer TA information from the target gNB to the WTRU before handover. Instead of the WTRU directly acquiring TA from the target cell after handover (which would cause link instability), the source gNB mediates by receiving TA information from the target gNB and providing it to the WTRU in advance, ensuring seamless connectivity during the handover process.
2Loss of time
If LTM events are triggered based on measurement conditions, then handover timing can be optimized, but system complexity increases due to additional configuration and triggering mechanisms
Solution Approach 1:
The patent applies universality by making the LTM measurement configuration serve multiple functions. The same measurement configuration is used both for triggering handover decisions and for providing timing advance information. The measurement event conditions serve dual purposes: evaluating whether handover should be triggered and determining the optimal timing for the handover execution, thereby reducing the need for separate configuration mechanisms.
Solution Approach 2:
The patent uses parameter changes by dynamically adjusting measurement event conditions based on NTN-specific parameters such as satellite ephemeris information and propagation delay characteristics. The measurement thresholds and triggering conditions are adapted to account for the dynamic nature of satellite orbits, allowing optimized handover timing without requiring completely separate configuration systems for terrestrial and non-terrestrial networks.
Data Source
AI summary
A wireless transmit/receive unit (WTRU) may receive radio resource control (RRC) configuration information. The WTRU may receive measurement configuration information including a beam level measurement condition associated with the NTN candidate cell and at least one measurement event condition. The WTRU may trigger an LTM event based on the beam level measurement condition and the at least one measurement event condition being satisfied. The WTRU may receive an indication to perform location-based pre-compensation associated with the NTN candidate cell. The WTRU may determine a first timing advance (TA) value associated with the NTN candidate cell based on the location-based timing pre-compensation. The WTRU may receive an indication to perform LTM to the NTN candidate cell. The WTRU may perform the LTM and may transmit a handover completion message to the NTN candidate cell.