LTE Handover Method Using Pre-Computed Time Advance
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Solution Overview
Problem
In the Long Term Evolution (LTE) system, the handover process is delayed due to the random access procedure required for uplink synchronization during cell handovers, leading to increased control plane and user plane data interruption delays.
Innovation Solution
The proposed method involves obtaining and utilizing the Time Advance (TA) of the target cell before handover, allowing the User Equipment (UE) to send a Handover Complete message on a resource corresponding to the UL Grant, thereby reducing the need for synchronization procedures and shortening handover delays. This includes schemes where the TA is obtained and forwarded by the source or target cell, and the UE receives the UL Grant to facilitate timely uplink signaling and data transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a random access procedure is used to acquire uplink synchronization with a target cell during handover, then the UE can achieve uplink synchronization, but the handover delay increases
Solution Approach 1:
The target cell determines and provides the Time Advance (TA) value to the UE before the handover is executed. This preliminary action allows the UE to have uplink synchronization information ready in advance, eliminating the need to perform random access procedure after handover, thus reducing handover delay while ensuring uplink synchronization reliability
Solution Approach 2:
The patent extracts the TA determination function from the post-handover random access procedure and moves it to the pre-handover phase, where the target cell determines the TA value based on timing advance information received from the source cell or through uplink signal detection, thereby removing the time-consuming random access step from the critical handover path
2Reliability
If a random access procedure is performed for uplink synchronization, then synchronization is achieved, but control plane handover delay increases
Solution Approach 1:
The target cell determines the Time Advance (TA) value before handover execution and provides it to the UE through the source cell in the handover command. This preliminary synchronization preparation eliminates the need for post-handover random access procedures, directly reducing control plane handover delay while maintaining synchronization reliability
3Reliability
If a random access procedure is used for uplink synchronization, then the UE can synchronize with the target cell, but user plane data interruption delay increases
Solution Approach 1:
The target cell determines and provides the TA value to the UE before handover is executed. This advance preparation of synchronization information allows the UE to immediately resume user plane data transmission after handover without waiting for random access procedure completion, thereby reducing user plane data interruption delay while ensuring synchronization reliability
Data Source
AI summary
Embodiments of the present invention disclose a handover method, User Equipment (UE), and a network side device, which can shorten a handover delay of a control plane and an interrupt delay of user plane data. A handover method includes: obtaining, by a UE, a Time Advance (TA) of a target cell before a handover; and obtaining an Uplink Grant (UL Grant) sent by the target cell; and then sending a Handover Complete message to the target cell with the TA on a resource that is corresponding to the UL Grant.