Conditional Handover with Delayed Secondary Cell Group Execution
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Solution Overview
Problem
In cellular telecommunications systems, particularly in multi-radio dual connectivity (MR-DC), the conditional handover (CHO) process is limited as it only prepares a single target primary cell, leading to issues when a user equipment (UE) needs to access multiple target secondary cells, with undefined order of accessing target PCell and PSCell, resulting in discrepancies between configured and actual cell connections.
Innovation Solution
The method involves the target master node (MN) synchronizing the UE to target secondary cells (PSCell) without immediate configuration, allowing delayed synchronization and measurements, with triggers via RRC, PDCCH, or MAC CE, and using a guard timer for dual connectivity de-configuration if conditions are not met.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE accesses target PCell but cannot connect to target PSCell, then handover to primary cell is completed, but dual connectivity configuration becomes inconsistent with actual connection state
Solution Approach 1:
The network prepares multiple target PSCells in advance as candidate cells before handover execution. When handover is triggered, the UE can immediately select from pre-prepared candidates without needing to establish new connections, thus ensuring reliable handover execution while avoiding configuration inconsistencies.
Solution Approach 2:
The network introduces an intermediary mechanism where the target gNB maintains a list of candidate PSCells and manages their preparation status. This intermediary layer coordinates between the handover execution and PSCell establishment, ensuring that configuration and actual connection states remain consistent.
2Reliability
If the UE waits for both CHO and CPC conditions to be met, then dual connectivity can be established, but handover execution time is delayed
Solution Approach 1:
The network performs preliminary preparation of multiple target PSCells before handover execution. These pre-prepared candidate cells are ready for immediate access, allowing the UE to establish dual connectivity quickly after handover without waiting for PSCell conditions to be met, thus reducing handover execution time while ensuring reliable dual connectivity establishment.
Solution Approach 2:
The system dynamically adjusts the handover execution strategy by allowing the UE to access pre-prepared candidate PSCells based on real-time conditions. The UE can selectively connect to available candidates without being constrained by rigid pre-defined conditions, enabling flexible and timely dual connectivity establishment.
3Adaptability or versatility
If the network prepares multiple target PSCells in advance, then UE can access target PSCell after handover, but network resource reservation increases
Solution Approach 1:
The network prepares a limited number of candidate PSCells (e.g., up to 3) in advance rather than all possible target PSCells. This partial preparation approach provides sufficient flexibility for the UE to access an appropriate target PSCell while avoiding excessive resource reservation, thus balancing adaptability with resource efficiency.
Solution Approach 2:
The network dynamically adjusts the number and configuration of pre-prepared candidate PSCells based on UE capability, service requirements, and network conditions. By changing parameters such as the maximum number of candidates and their configuration details, the system optimizes the balance between access flexibility and resource consumption.
Data Source
AI summary
The present invention is about conditional handover (CHO) in telecommunications networks, and a main point is to pass the responsibility to a target Master Node for triggering the UE to rapid access to Primary Secondary Cell after applying target Primary Cell configuration during a CHO-NR-DC handover. The target MN decides whether to wait further to execute CPC. If measurements are hopeful, completion of execution of the primary secondary cell for dual connectivity is postponed, and L3 measurement results are inspected from the UE. There are three variants, when the target MN requests the UE to access the target Secondary Node; namely RRC-based access target SN trigger, PDCCH-order-based variant and DL MCE-based variant.