A dual-mode mobile terminal is a mobile terminal capable of supporting two radio technologies having different communication schemes, and is mainly used in a region in which heterogeneous communication networks coexist. As a representative example of the dual-mode mobile terminal, many developers and companies are conducting intensive research into mobile terminals configured to use not only Long Term Evolution (LTE)-based wireless communication but also Code Divisional Multiple Access (CDMA)—based wireless communication. An enhanced High-Rate Packet Data (eHRPD) scheme may be used as a representative example of CDMA. The eHRPD is a new version of the 1xEV-DO upper layer protocol stack developed by the 3GPP2 standards committee so as to enable wireless communication network interoperability for LTE.
Although a dual-mode terminal capable of communicating with the LTE network and the eHRPD network according to the present invention will hereinafter be disclosed as an example for convenience of description and better understanding of the present invention, it is obvious to those skilled in the art that other wireless communication schemes can also be applied to the present invention without difficulty.
If a user equipment (UE) supports two different communication schemes, the UE may prefer to receive services through a high radio technology from the viewpoint of a general communication enterprise. That is, assuming that the UE supports the LTE scheme and the eHRPD scheme, the UE may prefer to receive a necessary service through the LTE network. However, service coverage of the eHRPD network is larger than that of the LTE network at an initial service step in which switching from the legacy eHRPD network to the LTE network begins. In the initial service step in which switching from the legacy eHRPD network to the LTE network begins, the service coverage of the eHRPD network is larger than that of the LTE network. If the UE is located at a coverage boundary of the LTE network under the above-mentioned situation, the UE may be handed over to the eHRPD network by a network configured handover condition. On the contrary, if the UE receives a necessary service through the eHRPD network, the UE periodically searches for an LTE cell. Then, the UE having searched for the LTE cell may attempt to immediately access the LTE cell without network control. In this case, if the UE is located at an area with poor coverage, such as a cell edge of the LTE cell or a shaded region, the UE again determines the network configured handover (HO) condition. If the network configured handover (HO) condition is satisfied, the UE is handed over to the eHRPD network. The above-mentioned phenomenon (i.e., ping pong phenomenon) may repeatedly occur in so far as the UE stays in a specific region in which the corresponding condition is satisfied.
The above-mentioned problem is based on the fact that a first condition in which the UE performs handover from the LTE network to the eHRPD network is different from a second condition in which the UE performs handover from the eHRPD network to the LTE network. Accordingly, the present invention defines a handover (HO) execution condition capable of solving the above problem, and proposes a method and apparatus for performing efficient handover on the basis of the defined HO execution condition.