RACH-less Conditional Handover for Wireless Latency Reduction
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Solution Overview
Problem
Existing wireless communication systems face challenges in reducing latency and signaling overhead during network handovers, particularly in conditional mobility scenarios where traditional network-initiated handovers introduce delays and interruptions.
Innovation Solution
The implementation of a user equipment (UE) that can perform a RACH-less conditional cell switch by receiving a conditional cell switch configuration from a source cell, determining if execution conditions are met, and selecting a target cell for handover based on valid timing advance (TA) and uplink (UL) grant information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional network-initiated handover procedures are used, then handover reliability is maintained through random access procedures, but handover latency and signaling overhead increase
Solution Approach 1:
The patent applies preliminary action by pre-configuring uplink grants and timing advance information for candidate target cells before handover execution. This allows the UE to immediately transmit uplink data upon handover without performing random access procedures, thereby reducing handover latency while maintaining reliability through pre-validated transmission parameters
2Reliability
If random access procedures are performed during handover, then uplink synchronization is achieved, but signaling overhead and handover complexity increase
Solution Approach 1:
The patent eliminates random access procedures by pre-obtaining and storing timing advance information and uplink grants for target cells before handover. The UE directly uses these pre-configured parameters for uplink transmission, simplifying the handover process while maintaining uplink synchronization through pre-validated timing parameters
Solution Approach 2:
The patent extracts and removes the random access procedure step from the handover process by utilizing pre-configured uplink resources. This extraction eliminates the need for interactive random access signaling while preserving the essential function of achieving uplink synchronization through pre-obtained timing advance information
3Speed
If conditional handover configurations are established, then handover speed is improved, but network signaling overhead increases due to multiple data exchanges
Solution Approach 1:
The patent reduces signaling overhead by pre-configuring comprehensive handover parameters including uplink grants and timing advance information in advance. This preliminary configuration minimizes the need for subsequent data exchanges during handover execution, allowing faster handover while reducing the volume of signaling messages required
Data Source
AI summary
A random access channel (RACH)-less conditional cell switch is provided. A user equipment (UE) receives and stores a candidate cell configuration including an execution condition of a conditional cell switch to the candidate cell. The UE selects the candidate cell as a target cell for the conditional cell switch on determination that the execution condition is met. The UE determines whether a valid timing advance (TA) and a valid uplink (UL) grant for initial UL transmission to the target cell is available. When a valid TA and a valid UL grant are available, UE transmits initial UL transmission to the target cell using the valid TA and the valid UL grant. When a valid TA is unavailable, the UE performs random access procedure to the target cell. When a valid UL grant is unavailable, the UE transmits a scheduling request to the target cell.