L1/L2 Triggered Handover with Selective Candidate Resource Reservation
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Solution Overview
Problem
The duration between LTM Handover (HO) preparation and execution is significant, and not all target candidate cell configurations result in LTM serving cell changes, leading to issues with resource reservation, including PRACH preambles, while data forwarding is slow and involves considerable overhead.
Innovation Solution
A method for preparing and executing LTM Handover by receiving L1 Measurement Reports at candidate gNB-DUs, determining radio conditions, reserving partial or full radio resources, and sending updated configurations to UE via gNB-DUs, reducing the need for RACH procedures and optimizing data forwarding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If LTM handover preparation is done early with candidate cell configurations, then handover execution can be faster, but the duration between preparation and execution becomes significant and resource reservation becomes inefficient
Solution Approach 1:
The patent applies preliminary action by preparing candidate cell configurations in advance and storing them in the UE. The network pre-configures multiple candidate cells with their parameters, and the UE stores these configurations locally. When handover is needed, the UE can quickly select and execute the appropriate candidate without waiting for real-time configuration setup, thereby reducing the lead time between preparation and execution while maintaining high execution efficiency.
2Adaptability or versatility
If resource reservation is done for all candidate cells, then handover options are available, but not all target candidate cell configurations result in LTM serving cell changes causing resource waste
Solution Approach 1:
The patent applies partial action by reserving resources selectively rather than for all candidate cells. The network reserves PRACH preambles and other critical resources only for candidate cells that are actually selected for handover execution. The UE stores multiple candidate configurations but only activates and reserves resources for the selected target cell, avoiding resource waste on configurations that are not used.
Solution Approach 2:
The patent applies local quality by tailoring resource reservation to specific local conditions. Each candidate cell configuration is evaluated based on local radio conditions and handover criteria, and resources are reserved only for configurations that meet the necessary conditions for actual handover execution. This ensures that resource reservation is optimized for each specific handover scenario rather than being applied uniformly to all candidates.
3Reliability
If RACH procedure is used for uplink synchronization, then timing advance can be acquired, but the process takes around 10-20 milliseconds causing additional delay
Solution Approach 1:
The patent applies preliminary action by acquiring timing advance information from candidate cells before the actual handover execution. The network pre-acquires TA values for candidate cells and stores them in the UE, or the UE performs preliminary TA acquisition during measurement phases. When handover is triggered, the UE can immediately use the pre-acquired TA information to establish uplink synchronization without waiting for the full RACH procedure, reducing the synchronization time from 10-20 milliseconds to a much faster process.
4Reliability
If data forwarding is performed to multiple target cells, then data continuity is maintained, but processing load and buffer occupancy overhead increase considerably
Solution Approach 1:
The patent applies partial action by forwarding data only to the selected target cell rather than to all candidate cells. The network identifies the optimal target cell based on handover criteria and radio conditions, and directs data forwarding only to that specific cell. This reduces the processing load and buffer occupancy overhead significantly compared to forwarding to multiple cells, while still maintaining data continuity through proper target cell selection.
Solution Approach 2:
The patent applies the extraction principle by separating the data forwarding function from the candidate cell configurations. Instead of maintaining data forwarding to all configured candidates, the system extracts and activates data forwarding only for the selected target cell. The UE and network dynamically determine which candidate cell becomes the active target and only establish data forwarding paths for that specific cell, eliminating unnecessary forwarding overhead to unused candidates.
Data Source
AI summary
A Layer 1-Layer 2 (L1/L2) Triggered Mobility (LTM) handover (HO) procedure, and method. A gNB-Centralized Unit User Plane (gNB-CU-CP) sends Radio Resource Control (RRC) messages with LTM candidate cell configuration of LTM candidate gNB-DUs. Based on the RRC messages, a Layer (L1) Measurement Report is sent to the LTM candidate gNB-DUs. In response, the LTM candidate gNB-DUs determine whether a radio condition of the LTM candidate gNB-DUs meet a predetermined resource reservation criteria. Based on meeting the predetermined resource reservation criteria, the LTM candidate gNB-DUs initiate reservation of radio resources for an LTM candidate cell for a LTM cell switch. The LTM candidate gNB-DUs send to the gNB-CU-CP an updated LTM candidate cell configuration. The gNB-CU-CP sends the updated radio resource configuration to the UE via the serving gNB-DU.