Patent ID: 8260297

Claim:
A method for performing an uplink timing synchronization procedure upon handover at a User Equipment (UE) in a mobile communication system, comprising: receiving a handover command message indicating handover to a target cell and representing whether the uplink timing synchronization procedure is required in the target cell, from a Node B; determining from the handover command message if the uplink timing synchronization procedure is required by determining whether a difference between uplink timings of a source cell and the target cell, detected from the handover command message, is set to a predetermined value; sending at least one of uplink signaling and uplink data to the target cell at an uplink timing of the source cell without performing the uplink timing synchronization procedure with the target cell after the handover to the target cell, if it is determined that the uplink timing synchronization procedure is not required; and acquiring an uplink timing of the target cell by performing the uplink timing synchronization procedure with the target cell after the handover to the target cell, and sending at least one of uplink signaling and uplink data to the target cell at the uplink timing of the target cell, if it is determined that the uplink timing synchronization procedure is required.