Satellite Assistance Handover Timing for NTN Reliability
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Solution Overview
Problem
Handover procedures in wireless communication systems, particularly in non-terrestrial networks (NTN) and 6G networks, face challenges due to the expiration of validity timers for satellite assistance information, leading to potential handover failures and increased interruption times.
Innovation Solution
The method involves receiving satellite assistance information with a validity timer, determining if the epoch time is in the past, and if so, updating the information and modifying handover timers or requirements such as the T304 timer to ensure valid satellite assistance is available before completing the handover, thereby relaxing interruption time requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE waits for valid satellite assistance information before completing handover, then handover reliability is improved, but handover interruption time increases
Solution Approach 1:
The network provides satellite assistance information in advance through the handover configuration message, including epoch time and ephemeris data. The UE can determine validity by comparing epoch time with current time, allowing handover to proceed without waiting for additional information acquisition.
Solution Approach 2:
The UE autonomously determines the validity of satellite assistance information by comparing the provided epoch time with current time and checking the validity timer. This self-validation mechanism eliminates the need for additional network verification steps, reducing handover interruption time while ensuring reliability.
2Speed
If the UE uses satellite assistance information with expired validity timer, then handover speed is improved, but communication reliability deteriorates
Solution Approach 1:
The handover configuration message includes a validity timer that provides feedback on the freshness of satellite assistance information. The UE monitors this timer and can determine whether the information is still valid before completing handover, ensuring communication reliability while maintaining handover speed.
Solution Approach 2:
The network dynamically adjusts the validity timer parameter based on satellite movement characteristics and signal conditions. By changing this parameter, the system balances between using outdated information (faster handover) and ensuring information accuracy (better reliability).
3Measurement precision
If the UE requests updated satellite assistance information during handover, then information accuracy is improved, but handover interruption time increases
Solution Approach 1:
The network provides updated satellite assistance information (epoch time and ephemeris) in advance within the handover configuration message. This preliminary provision of accurate information eliminates the need for additional requests during handover, maintaining both accuracy and speed.
Solution Approach 2:
The UE skips the step of requesting updated information during handover by using the pre-provided satellite assistance information with validity indicators. This allows the handover to proceed rapidly while still using accurate information, as the validation is done locally without network round-trips.
Data Source
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AI summary
There is provided an apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: receiving, from a serving cell, a configuration message for a handover to a target cell associated with a different satellite assistance information than satellite assistance information associated with the serving cell, wherein the configuration message is indicative of at least: the satellite assistance information associated with the target cell; and a validity timer for defining validity of at least part of the satellite assistance information; wherein the satellite assistance information comprises at least: an epoch time and corresponding satellite assistance information, which is to be applied after reaching the epoch time; determining, based on at least the epoch time, whether to modify a handover timer and/or one or more requirements on handover completion.