Handover Command Segmentation for Zero Interruption
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Solution Overview
Problem
The enhanced make-before-break handover procedure in LTE and NR systems faces challenges in ensuring mobility robustness and zero interruption time due to the timing of the handover command transmission, which can lead to unsuccessful receipt of the command by the UE and unstable radio links during the transition from the source to the target BS.
Innovation Solution
The proposed solution involves providing the handover command early enough for successful receipt by the UE, decoupling the handover preparation phase from the execution phase, and configuring a detach condition based on signal strength differences between the source and target BSs, allowing the UE to maintain connection with the source BS until the target BS's radio link becomes stable.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the handover command is provided early enough to ensure successful receipt by the UE, then mobility robustness is improved, but the UE may detach too early from the source BS before the target BS radio link is stable
Solution Approach 1:
The handover procedure is segmented into distinct phases: preparation phase where the HO command is provided early to improve robustness, and execution phase where the detach condition ensures stable connection transfer. This segmentation allows independent optimization of each phase - early command provision for reliability, and conditional detach for stability.
Solution Approach 2:
The handover command is provided in advance during the preparation phase, before the actual handover execution. This preliminary action ensures the UE receives and processes the command with high probability while maintaining connection to the source BS, allowing stable execution later when radio conditions are favorable.
2Loss of time
If the UE detaches immediately from the source BS after accessing the target BS, then service interruption time is reduced, but the radio link stability during transition is compromised
Solution Approach 1:
The detach timing is made dynamic through the detach condition mechanism. Instead of a fixed immediate detach, the UE evaluates signal strength differences between source and target BSs and detaches only when the target BS signal exceeds the source BS signal by the configured threshold. This dynamic approach adapts to real-time radio conditions to ensure stability.
3Reliability
If the source BS continues exchanging user plane packets until UE detaches, then data transmission reliability is improved, but the handover procedure complexity increases
Solution Approach 1:
The UE autonomously determines when to detach from the source BS by evaluating the detach condition (signal strength difference between target and source BSs). This self-service mechanism eliminates the need for complex network-controlled detach timing, reducing procedure complexity while maintaining reliable data transmission until appropriate detach moment.
Data Source
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AI summary
A source network apparatus (10) which provides access for a user equipment (30) to a communication network transmits (S102) a handover command to the user equipment (30), the handover command indicating a target network apparatus (20) for providing access for the user equipment (30) to the communication network, and a detach condition on when the user equipment (30) is to detach from the source network apparatus (10) after having accessed the target network apparatus (20) (S204) and received user plane data packets from the target network apparatus (20) (S205), wherein the source network apparatus (10) continues exchanging user plane data packets with the user equipment (30) (S101, S103) until the user equipment (30) detaches (S306) from the source network apparatus (10).