Cell Handover Timing Advance Validity During L1/L2 Mobility
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Solution Overview
Problem
The validity of the time advance (TA) acquired by a terminal device during cell handover in wireless communication systems is unclear, which affects the reliability of communication.
Innovation Solution
The validation duration of the TA for the target cell is determined based on the time alignment timer (TAT) of the terminal device, ensuring the TA's validity during its operational period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the terminal device acquires TA in advance during L1/L2 triggered mobility, then the handover speed is improved, but the reliability of communication deteriorates due to unclear TA validity
Solution Approach 1:
The terminal device performs random access to the target cell and acquires the time advance (TA) value before the handover is officially executed. This preliminary acquisition of TA enables faster handover execution since the timing adjustment information is already available, eliminating the need to perform random access after handover. The source cell or target cell may also pre-determine and notify the TA validity duration, further accelerating the handover process.
Solution Approach 2:
The system implements a feedback mechanism where the terminal device reports the acquired TA value and its validity duration to the source cell or target cell. The network side receives this feedback and uses it to make informed decisions about handover execution. This feedback loop ensures that the network is aware of the TA validity status, enabling reliable communication while maintaining fast handover performance.
2Productivity
If the TA validity duration is extended to enable faster handover, then the handover efficiency is improved, but the risk of using invalid TA increases
Solution Approach 1:
The validity duration of the acquired TA is determined in advance, either by the terminal device based on its movement speed or by the network side (source cell or target cell). This preliminary determination of validity duration allows the terminal to know exactly how long the TA remains valid, enabling efficient handover execution within the valid period while avoiding use of expired TA values.
Solution Approach 2:
The terminal device provides feedback to the network side regarding the TA validity duration, creating an information loop that allows the network to track TA validity status. This feedback mechanism ensures that handover decisions are made with accurate knowledge of TA validity, preventing the use of expired TA values while maximizing handover efficiency within the valid time window.
3Adaptability or versatility
If the terminal device determines TA validity independently, then the handover autonomy is improved, but the coordination with network side deteriorates
Solution Approach 1:
The terminal device is empowered to independently determine the validity duration of the acquired TA based on its movement characteristics. This preliminary autonomous determination simplifies the handover process by allowing the terminal to make its own judgment about TA validity without complex real-time coordination with the network, while still maintaining overall system coordination through subsequent feedback.
Solution Approach 2:
While the terminal device independently determines TA validity, it maintains coordination with the network side by reporting the determined validity duration through feedback. This feedback mechanism allows the network to be informed of the terminal's autonomous decision, enabling the network to provide guidance or override if necessary, thus balancing autonomy with coordination.
Data Source
AI summary
The present disclosure provides a method for cell handover, a terminal device, and a network device. One example method includes: receiving, by a terminal device, a first time advance (TA) during layer 1 (L1)/layer 2 (L2) triggered mobility, wherein the first TA is a TA of the terminal device relative to a target cell, and the first TA is valid during an operational period of a first time alignment timer (TAT) of the terminal device.