In the 3rd Generation Partnership Project (3GPP) that is a mobile communication system standardization project, introduction of a device-to-device (D2D) proximity service as a new function after Release 12 is under review (see Non Patent Literature 1).
The D2D proximity service (D2D ProSe) is a service that enables direct D2D communication to be performed in a synchronous cluster including a plurality of user terminals which are synchronized with one another. The D2D proximity service includes a D2D discovery process (ProSe Discovery) of discovering a nearby terminal and D2D communication (ProSe Communication) that is direct D2D communication.
Here, a serving cell can notify a user terminal of another frequency that supports the D2D proximity service and is different from a frequency of the serving cell through system information (a system information block (SIB)). The user terminal may monitor a D2D signal that is transmitted at another frequency that is notified of through the SIB.
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