An operation method of a terminal includes receiving configuration information from a serving base station; measuring channel states of the serving base station and a target base station; when a difference between received signal strengths of the serving base station and the target base station is not less than a handover preparation offset, determining that a handover preparation event has occurred and transmitting a measurement report message to the serving base station; and when the difference is equal to or greater than a handover execution offset, determining that a handover execution event has occurred and transmitting a handover indication message informing of execution of a handover to the target base station. The channel state is normal state, abnormal state, or RLF state, and the configuration information indicates a different handover preparation offset and a different handover execution event according to the channel state.