In a mobile communication system, handover means a procedure that, when a user equipment (UE) of which call is connected with a base station is disconnected from a corresponding base station service area and moves to an adjacent base station service area, the user equipment is automatically synchronized with a new communication channel of the adjacent base station and continues to maintain communication. In a broadband wireless communication system which is characterized in data packet communication of large capacity, a handover scheme more efficient than the existing handover scheme is required considering limited communication resources.
FIG. 1 is a flow chart illustrating a handover procedure in a mobile communication system according to the related art.
If a source base station (source eNB) is satisfied with a designated standard or a specific event occurs, a user equipment transmits a measurement report message to the source base station (S110). The source base station means a network node which is connected with the user equipment before handover is performed. The source base station determines handover if it is determined that handover is required referring to the measurement report message from the user equipment (S115).
The source base station transmits a handover preparation message to a target base station (target eNB), wherein the handover preparation message includes UE context information (S120). The target base station means a base station which controls a new cell to which the user equipment moves through handover. The UE context information includes information related to quality of service (QoS) received from the source base station to the user equipment, a radio bearer type, etc.
The target base station determines whether to allow a request of handover considering its wire and wireless resources. If the target base station determines to allow a request of handover, the target base station acquires resources for connection with the user equipment (S125), and forwards resource setup information of the user equipment to the source base station along with a new temporary identifier (C-RNTI) of the user equipment (S130).
The source base station transmits a handover command to the user equipment (S140), and starts to transmit user data to the target base station. The user equipment performs signaling of a first layer (Layer 1) and a second layer (Layer 2) to reset a wireless environment including timing synchronization with the target base station (S150). The user equipment receives timing information from the target base station and then transmits a handover acknowledgement message to the target base station (S160). The target base station transmits a handover completion message to the source base station to notify success of handover (S170). Afterwards, the source base station releases all resources of the user equipment. The target base station requests a core network (MME/UPE) to update a location of the user equipment (S180). The core network switches path setup of the user equipment to forward user data, which have been conventionally forwarded to the source base station, to the target base station (S190).
However, the aforementioned method of performing handover according to the related art does not consider a connection setup state between the user equipment and the source base station before handover is performed or a data transmission and reception state. For this reason, the user equipment may perform an unnecessary action after handover completions depending on the connection setup state with the source base station before handover is performed or the data transmission and reception state. In this case, a problem occurs in that the power of the user equipment may be used inefficiently.