Single Active Protocol Stack Handover Recovery Mechanism
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Solution Overview
Problem
Current 5G wireless systems face challenges in achieving zero ms interruption during handover due to the complexity of dual active protocol stack (DAPS) handover, which is not fully supported in 3GPP Release 16, and existing recovery mechanisms like condition handover (CHO) lead to unnecessary interruption time and increased signaling overhead.
Innovation Solution
A recovery mechanism for single active protocol stack (SAPS) handover that involves a user equipment (UE) performing a random access procedure with a target base station, starting a timer upon receiving a random access response, and completing handover to the target base station if a random access complete message or radio resource control connection reconfiguration message is not received within a predefined duration, thereby informing the target base station of the failure to send or receive these messages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If dual active protocol stack (DAPS) handover is used to achieve zero ms interruption, then handover interruption time is reduced, but device complexity and signaling overhead increase
Solution Approach 1:
The patent extracts the essential functionality of DAPS handover (maintaining protocol stack during handover) while removing the complex dual-stack implementation. It uses a simplified single active protocol stack approach where the UE maintains the source stack during handover preparation and switches to the target stack after random access, achieving near-zero interruption without the complexity of maintaining two full protocol stacks simultaneously.
Solution Approach 2:
The patent applies preliminary action by having the target base station prepare the random access procedure and send the random access response before the actual handover execution. The UE starts a timer upon receiving the random access response and completes handover based on timer expiration or message reception, pre-establishing the timing framework before the critical handover moment.
2Reliability
If condition handover (CHO) recovery mechanism is used, then handover reliability is improved, but interruption time and signaling overhead increase
Solution Approach 1:
The patent implements feedback by having the UE monitor for the arrival of the random access complete message or radio resource control connection reconfiguration message from the source base station. If these messages are not received within a predefined duration (timer expiration), the UE sends a feedback indication to the target base station about the handover failure, enabling reliable recovery without the interruption time associated with CHO.
3Device complexity
If single active protocol stack (SAPS) handover is used, then device complexity is reduced, but handover reliability decreases due to radio issues on source base station link
Solution Approach 1:
The patent applies preliminary action by having the UE perform random access to the target base station and receive the random access response before finalizing the handover. The UE starts a timer upon receiving this response and uses the timer expiration or message reception as the trigger for completing handover, pre-establishing a reliable timing mechanism that ensures handover completion even when source base station links are problematic.
Data Source
AI summary
Systems, methods, apparatuses, and computer program products for a recovery mechanism for single active protocol stack handover. A method may include performing a random access procedure with a target base station. The method may also include receiving, during the random access procedure, a random access response from the target base station. A timer may be started for a predefined duration upon receiving the random access response. The method may further include, when a random access complete message is not sent to a source base station, or a radio resource control connection reconfiguration message is not received from the source base station within the predefined duration, informing the target base station about the failure to send the random access complete message to the source base station, or the failure to receive the radio resource control connection reconfiguration message from the source base station. Handover may be completed to the target base station upon expiration of the timer.