RACH-less Handover via Pre-configured Uplink Grants
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Solution Overview
Problem
In mobile communication systems, the random access procedure during handover between cells can cause communication interruptions and inefficiencies, particularly when cells are not fully synchronized, leading to delays and resource mismanagement.
Innovation Solution
A method and apparatus for user equipment to perform dual connectivity with base stations, allowing the skipping of the random access procedure by transmitting capability information to the master base station, receiving an uplink grant and timing advance value, and using these to perform uplink transmissions to a third base station, thereby omitting the random access procedure during handover.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the random access procedure is performed during handover, then the handover process is complete and reliable, but communication interruption time increases and network efficiency decreases
Solution Approach 1:
The network side performs preliminary actions by pre-configuring uplink grant and timing advance information before the handover occurs. The source base station obtains these parameters from the target base station in advance and includes them in the handover command, allowing the terminal to skip the random access procedure and directly perform uplink synchronization with the target cell.
Solution Approach 2:
The invention extracts and removes the random access procedure from the handover process. By taking out this unnecessary step, the handover can be completed more quickly without affecting reliability, as the terminal already has the necessary uplink grant and timing advance information provided through the handover command.
2Reliability
If the random access procedure is performed during handover, then uplink synchronization is achieved, but network resource management efficiency decreases
Solution Approach 1:
The target base station provides feedback information (uplink grant and timing advance) to the source base station, which then forwards it to the terminal in the handover command. This feedback mechanism ensures the terminal has accurate uplink synchronization parameters without needing to perform the random access procedure, improving resource management efficiency.
3Loss of time
If the random access procedure is skipped during handover, then communication interruption time is reduced, but compatibility with existing systems decreases
Solution Approach 1:
The invention changes the parameter transmission method by including uplink grant and timing advance information directly in the handover command message. This parameter change allows the system to support both traditional handover with random access and the new RACH-less handover mode, maintaining backward compatibility while enabling faster handover when conditions permit.
Data Source
AI summary
User equipment, apparatus and method perform dual connectivity with a first base station acting as a master base station and a second base station acting as a secondary base station, transmit to the master base station capability information indicating that the user equipment supports a function of skipping a random access procedure, and receive from the master base station, a message instructing to change the secondary base station from the second base station to a third base station. The message includes information indicating that random access procedure for the third base station is skipped and an including an uplink grant indicating radio resources allocated by the third base station and a timing advance (TA) value to be applied to an uplink transmission to the third base station. The user equipment transmits the uplink transmission to the third base station by using the uplink radio resources indicated by the uplink grant.