NTN Handover Epoch Timing for Target Cell Synchronization
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Solution Overview
Problem
In non-terrestrial networks (NTN), user equipment (UE) faces a deadlock situation during handover procedures due to the need for synchronization with a target cell, which requires determining an epoch time based on changing ephemeris information of satellites, especially in low-Earth orbits, without a clear reference time.
Innovation Solution
The UE determines an epoch time using an epoch index received from the serving cell, which is converted to reference the serving cell's timing, allowing synchronization with the target cell by incorporating ephemeris information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the UE waits to obtain epoch time from the target cell before performing synchronization, then synchronization accuracy is improved, but handover latency increases and the UE cannot complete the handover in a timely manner
Solution Approach 1:
The source base station performs preliminary actions by determining the epoch time of the target cell using ephemeris information and epoch index before the handover command is executed. The source base station then provides this epoch time information to the UE in the handover command, allowing the UE to immediately perform synchronization without waiting to obtain epoch time from the target cell, thus resolving the deadlock and reducing handover latency.
2Productivity
If the UE performs synchronization without accurate epoch time, then handover speed is improved, but synchronization accuracy deteriorates and communication quality is compromised
Solution Approach 1:
The source base station acts as an intermediary by calculating and providing the epoch time information to the UE through the handover command. This intermediary action enables the UE to perform accurate synchronization immediately without needing to wait for or directly obtain epoch time from the target cell, thus maintaining both high handover speed and synchronization accuracy.
3Device complexity
If the epoch index is not converted to reference serving cell timing, then system complexity is reduced, but synchronization accuracy between serving cell and target cell deteriorates
Solution Approach 1:
The source base station performs a parameter transformation by converting the epoch index from target cell timing reference to serving cell timing reference. This parameter change ensures that the epoch time information provided to the UE is consistent with the serving cell's timing, enabling accurate synchronization while maintaining relatively simple system architecture. The conversion uses the known timing relationship between serving cell and target cell.
Data Source
AI summary
Aspects are described for a user equipment (UE) comprising a transceiver configured to enable wireless communication with a serving cell and a target cell and a processor communicatively coupled to the transceiver. The processor is configured to receive a handover command from the serving cell. The handover command comprises an epoch index and ephemeris information of the target cell. The processor is further configured to determine an epoch time of the target cell based on the epoch index and perform time synchronization with the target cell using the epoch time and the ephemeris information.