Inter-RAT Handover With Connected-Mode Continuity
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Solution Overview
Problem
Existing UE implementations do not efficiently handle handover events between base stations of different types (e.g., gNB and ng-eNB) connected to the same core network, leading to inefficient radio connection management and potential transitions to idle modes.
Innovation Solution
The UE determines whether to continue operating in connected mode or transition to idle mode by utilizing a non-access stratum protocol entity, such as a 5GMM entity, and adjusts radio bearer management through RRC entities to maintain connectivity during handovers between base stations of different types connected to the same core network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the UE releases existing radio connection and/or radio bearer during handover between base stations of different types, then the handover procedure can be completed, but the connectivity is interrupted and the UE transitions to idle mode
Solution Approach 1:
The target base station pre-configures radio bearers and establishes PDCP/SDAP entities before the handover is executed. This preliminary setup ensures that when the handover occurs, the radio connections are already in place and can be immediately activated without interruption or transition to idle mode.
Solution Approach 2:
The patent maintains continuous radio connection during handover by preserving PDCP and SDAP entities across the handover event. The radio bearers remain active throughout the transition, eliminating gaps in connectivity and preventing transitions to idle mode, thus ensuring continuous useful action.
2Reliability
If the UE maintains existing radio bearers during handover between base stations of different types, then connectivity continuity is improved, but additional configuration and management complexity is required
Solution Approach 1:
The patent applies universal configuration where the target base station provides complete PDCP and SDAP configurations that can be used across different base station types. This multi-functional approach allows the same configuration mechanisms to work for both intra-type and inter-type handovers, reducing the need for type-specific complexity while maintaining connectivity.
3Device complexity
If the UE transitions to idle mode during handover, then resource management is simplified, but service continuity and connection efficiency are degraded
Solution Approach 1:
The patent prevents transitions to idle mode by maintaining active PDCP and SDAP entities throughout the handover process. Radio bearers continue to operate without interruption, ensuring service continuity and keeping the UE in connected mode, thereby avoiding the simplicity of idle state transitions at the cost of maintaining active resource management.
Data Source
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AI summary
A user equipment (UE) for handling mobility between base stations receives, from a source base station, a command to hand over to a target base station, while the UE operates in an mobility management (MM)-connected mode and communicates with the source base station via a radio bearer (1002), determines that the source base station and the target base station operate according to different radio access technologies (RATs) and connect to a same core network (CN) (1004), and in response to an indication that a handover completed in accordance with the command, continues to operate in the MM-connected mode (1006).