Inter-DU L1/L2 Mobility Candidate Setup for Low-Latency Handover
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Solution Overview
Problem
Current 5G wireless networks face inefficiencies in L1/L2 inter-cell mobility due to unclear roles of neighbor DUs in configuring UEs for L1/L2 inter-cell mobility, leading to longer latency, increased signaling overhead, and longer interruptions during handovers.
Innovation Solution
Implement flexible signaling techniques allowing interaction between the serving CU, DU, and neighbor DUs to configure UEs with L1/L2 inter-cell mobility candidates, including message exchanges for UE context setup and configuration with neighbor DUs, enabling efficient L1/L2 inter-cell mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If traditional L3-based inter-cell mobility procedures are used, then reliability of handover is maintained, but latency and interruption time increase significantly
Solution Approach 1:
The patent applies preliminary action by configuring L1/L2 mobility candidate cells in advance through RRC reconfiguration messages before handover is needed. The UE stores configurations for multiple candidate cells provided by neighbor DUs, so when handover is required, the UE can immediately switch to a pre-configured candidate cell without waiting for new configuration, thereby reducing handover latency while maintaining reliability through pre-validated candidate selections.
2Productivity
If L1/L2 mobility configuration is implemented without clear neighbor DU roles, then signaling overhead is reduced, but mobility efficiency deteriorates due to unclear configuration procedures
Solution Approach 1:
The patent applies segmentation by dividing the mobility management functionality between the serving DU, neighbor DUs, and CU. Each entity has a specific role: the serving DU identifies candidate cells, neighbor DUs provide their cell configurations, and the CU coordinates the overall procedure. This segmented approach clarifies the previously unclear roles, enabling efficient L1/L2 mobility while maintaining manageable signaling complexity through defined responsibilities.
Solution Approach 2:
The patent uses the CU as an intermediary that coordinates between the serving DU and neighbor DUs. The CU receives configuration information from neighbor DUs, processes it through the serving DU, and delivers RRC reconfiguration messages to the UE. This intermediary role streamlines the interaction between multiple entities, reducing signaling complexity while improving mobility efficiency through coordinated configuration delivery.
3Adaptability or versatility
If multiple candidate cells from multiple neighbor DUs are configured, then mobility flexibility is improved, but signaling overhead increases
Solution Approach 1:
The patent applies merging by consolidating configuration information from multiple neighbor DUs into single RRC reconfiguration messages. Instead of separate signaling exchanges with each neighbor DU, the serving DU collects configurations from multiple candidate cells and delivers them together in one or more RRC messages to the UE. This merging approach maintains mobility flexibility by providing multiple candidate cells while reducing signaling overhead through batched configuration delivery.
Data Source
AI summary
Embodiments include methods for a user equipment (UE) configured to communicate with a radio access network (RAN) node comprising a central unit (CU) and a distributed unit (DU). Such methods include receiving, from the CU via the DU, a reconfiguration message that includes configurations associated with each of at least one candidate cell for L1/L2-based inter-cell mobility from a serving cell provided by the DU. The candidate cells are provided by one or more neighbor DUs. Such methods include storing the received configurations and receiving, from the DU, a lower layer signalling message including a command for the UE to change its serving cell to a first candidate cell, for which a configuration was received in the reconfiguration message. Such methods include performing an L1/L2 mobility procedure towards the first candidate cell and communicating in the first candidate cell according to the stored configuration associated with the first candidate cell.