According to the first embodiment, when a collision occurs among D2D signals, a priority may be assigned in an order of a discovery signal>SA>data, and D2D transmission may be executed based on the same. In this instance, as a main consideration, a discovery signal may have a long transmission period (for example, few seconds), and a delay in reception of a D2D discovery signal may be prevented by receiving a D2D discovery signal preferably within a single discovery period.

For example, when transmission/reception of a discovery signal occurs in parallel with transmission/reception of SA, the transmission/reception of the discovery signal is always prioritized over the transmission/reception of the SA. Therefore, the method may be considered as a method that prioritizes the transmission/reception of a discovery signal.

According to the first embodiment, when a discovery Tx signal and an SA Tx signal are generated in parallel on the same subframe, the SA Tx signal may be dropped. A transmission period of the discovery signal is longer than general D2D communication (SA, data) signals and thus, not missing a discovery signal in a discovery period is important. Therefore, according to the first embodiment, a delay in transmission/reception of a discovery signal may be minimized.

Additionally, when identical D2D signals collide on different carriers (PLMNs or cells), a D2D signal corresponding to a serving cell (or PLMN) may be preferentially transmitted or received.